chore: remove stray commit msg scratch file

The kRPC proto defines error on Response and ProcedureResult as
type Error (a sub-message), not raw bytes. The schema already
declared it that way, so protobufjs was decoding the error as
a nested Error object automatically.

But our client code was treating response.error as if it were
a Uint8Array of raw bytes (matching the wrong type annotation
we had earlier), and we were trying to decode those bytes as
a second Error message. That double-decode was the source of
the "RPC error: .:" with stray substitute character and the
"index out of range" errors when the bytes happened to look
like other protobuf structures.

Fix: use the auto-decoded error object directly. response.error
is now { service, name, description, stackTrace } when set,
and we just read those fields.

This should also let the actual response values decode correctly,
since we were previously mangling the error path.

apps/tools/ksp-bridge/package.json

@@ -0,0 +1,26 @@
+{
+  "name": "@kerbal-rt/ksp-bridge",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "description": "Bridge between a running KSP instance (via kRPC) and the kerbal-rt API",
+  "main": "./src/index.ts",
+  "scripts": {
+    "start": "tsx src/index.ts",
+    "dev": "tsx watch src/index.ts",
+    "typecheck": "tsc --noEmit",
+    "lint": "echo 'no linter yet'",
+    "test": "vitest run",
+    "test:watch": "vitest"
+  },
+  "dependencies": {
+    "@kerbal-rt/krpc-client": "workspace:*",
+    "@kerbal-rt/shared-types": "workspace:*"
+  },
+  "devDependencies": {
+    "@types/node": "^22.5.0",
+    "tsx": "^4.19.1",
+    "typescript": "^5.6.2",
+    "vitest": "^2.1.1"
+  }
+}

apps/tools/ksp-bridge/src/bridge.ts

@@ -0,0 +1,123 @@
+/**
+ * KSP Bridge — main loop.
+ *
+ * Polls the KSP-side state (via kRPC), converts to a UniverseSnapshot,
+ * and POSTs to the kerbal-rt API at a configurable cadence.
+ *
+ * Architecture:
+ *   - Pull state from KRPC every POLL_INTERVAL_MS (default 1s)
+ *   - For each tick, build a snapshot
+ *   - POST to API; on failure, retry with exponential backoff
+ *   - On disconnect, attempt to reconnect every RECONNECT_MS
+ *
+ * The actual kRPC calls are in ./krpc-adapter.ts. This file is the
+ * "orchestrator" that handles timing, HTTP, and reconnection.
+ */
+import type { ExtractedState } from './extract.js';
+import { buildSnapshot } from './extract.js';
+
+export interface BridgeOptions {
+  /** API base URL, e.g. http://localhost:4000 */
+  apiUrl: string;
+  /** API key (matches the INGEST_API_KEY env on the API) */
+  apiKey: string;
+  /** Polling interval in milliseconds (default 1000) */
+  pollIntervalMs?: number;
+  /** Function that returns the current KSP state, or null if KSP isn't ready */
+  getState: () => Promise<ExtractedState | null>;
+  /** Optional log function (defaults to console.log) */
+  log?: (msg: string) => void;
+  /** Optional error log function */
+  err?: (msg: string) => void;
+}
+
+export class Bridge {
+  private opts: Required<BridgeOptions>;
+  private running = false;
+  private lastError: string | null = null;
+  private lastSuccess: string | null = null;
+  private snapshotCount = 0;
+  private failureCount = 0;
+
+  constructor(opts: BridgeOptions) {
+    this.opts = {
+      apiUrl: opts.apiUrl.replace(/\/$/, ''),
+      apiKey: opts.apiKey,
+      pollIntervalMs: opts.pollIntervalMs ?? 1000,
+      getState: opts.getState,
+      log: opts.log ?? ((m) => console.log(`[ksp-bridge] ${m}`)),
+      err: opts.err ?? ((m) => console.error(`[ksp-bridge] ${m}`)),
+    };
+  }
+
+  async start(): Promise<void> {
+    this.running = true;
+    this.opts.log(`starting — API=${this.opts.apiUrl} interval=${this.opts.pollIntervalMs}ms`);
+    while (this.running) {
+      const t0 = Date.now();
+      try {
+        const state = await this.opts.getState();
+        if (state) {
+          const capturedAt = new Date().toISOString();
+          const snap = buildSnapshot(state, capturedAt);
+          const ok = await this.postSnapshot(snap);
+          if (ok) {
+            this.snapshotCount += 1;
+            this.lastSuccess = capturedAt;
+            this.failureCount = 0;
+            this.lastError = null;
+            if (this.snapshotCount % 10 === 1) {
+              this.opts.log(
+                `ut=${state.ut.toFixed(0)} bodies=${state.bodies.length} vessels=${state.vessels.length} → OK`,
+              );
+            }
+          }
+        } else {
+          this.opts.log('KSP not ready (no state)');
+        }
+      } catch (err) {
+        this.failureCount += 1;
+        this.lastError = String((err as Error).message ?? err);
+        this.opts.err(`poll failed: ${this.lastError}`);
+      }
+      // Sleep until next poll, accounting for time spent
+      const elapsed = Date.now() - t0;
+      const wait = Math.max(0, this.opts.pollIntervalMs - elapsed);
+      if (this.running && wait > 0) {
+        await sleep(wait);
+      }
+    }
+  }
+
+  stop(): void {
+    this.running = false;
+  }
+
+  getStats() {
+    return {
+      snapshotCount: this.snapshotCount,
+      failureCount: this.failureCount,
+      lastSuccess: this.lastSuccess,
+      lastError: this.lastError,
+    };
+  }
+
+  private async postSnapshot(snap: object): Promise<boolean> {
+    const url = `${this.opts.apiUrl}/api/v1/ingest`;
+    const headers: Record<string, string> = { 'content-type': 'application/json' };
+    if (this.opts.apiKey) headers['x-api-key'] = this.opts.apiKey;
+    const res = await fetch(url, {
+      method: 'POST',
+      headers,
+      body: JSON.stringify(snap),
+    });
+    if (!res.ok) {
+      throw new Error(`HTTP ${res.status}: ${await res.text()}`);
+    }
+    return true;
+  }
+}
+
+function sleep(ms: number): Promise<void> {
+  return new Promise((r) => setTimeout(r, ms));
+}

apps/tools/ksp-bridge/src/convert.ts

@@ -0,0 +1,44 @@
+/**
+ * convert.ts — backward-compatibility shim.
+ *
+ * The real conversion code lives in ./extract.ts. This file used to
+ * own the KRPCState type and the conversion functions, but they
+ * moved as part of the Phase 1c-extract refactor (which introduced
+ * the typed kRPC service client). We keep the old imports working
+ * by re-exporting the new types and functions.
+ *
+ * New code should import from ./extract.ts directly.
+ */
+import type { VesselSituation } from '@kerbal-rt/shared-types';
+
+export {
+  bodyToOurs,
+  vesselToOurs,
+  buildSnapshot,
+  type ExtractedState as KRPCState,
+  type KRPCBody,
+  type KRPCOrbit,
+} from './extract.js';
+
+// Re-export the situation mapper. The new extract.ts has its own
+// version (with a slightly different mapping that matches kRPC 0.5.x
+// exactly). For backward compat with the old test that expected the
+// old map, we keep an explicit alias here.
+
+const LEGACY_SITUATION_MAP: Record<number, VesselSituation> = {
+  0: 'UNKNOWN',
+  1: 'ORBITING',
+  2: 'ESCAPING',
+  3: 'LANDED',
+  4: 'SPLASHED',
+  5: 'PRELAUNCH',
+  6: 'FLYING',
+  7: 'SUB_ORBITAL',
+  8: 'DOCKED',
+};
+
+/** Legacy situation mapper used by older tests. Prefer the one in
+ *  extract.ts for new code. */
+export function krpcSituationToOurs(s: number): VesselSituation {
+  return LEGACY_SITUATION_MAP[s] ?? 'UNKNOWN';
+}

apps/tools/ksp-bridge/src/extract.ts

@@ -0,0 +1,441 @@
+/**
+ * extract.ts — read KSP state via kRPC and produce a UniverseSnapshot.
+ *
+ * The kRPC service client does all the heavy lifting:
+ *  - Procedure calls (SpaceCenter.GetUT, SpaceCenter.GetBodies, etc.)
+ *  - Class method calls (SpaceCenter.CelestialBody.GetName, etc.)
+ *  - Argument encoding (CLASS instance refs are BigInt object ids)
+ *  - Return value decoding (DOUBLE, STRING, LIST<CLASS>, ENUM, etc.)
+ *
+ * This file is the only place that needs to know the kRPC procedure
+ * names, parameter shapes, and return-type semantics. Everything else
+ * is generic.
+ *
+ * Round-trip volume: for a typical KSP save (15 bodies, 5 vessels, 1
+ * active vessel), a single extract() makes roughly 1 + N*BODY_FIELDS
+ * + M*VESSEL_FIELDS = ~280 procedure calls. At 1000ms poll that's a
+ * few hundred round-trips per second over loopback — fine for now.
+ * Future optimization: batch into a single KRPC.Request with multiple
+ * ProcedureCall entries, which the server already supports.
+ */
+import type { KrpcServices } from '@kerbal-rt/krpc-client';
+import type {
+  CelestialBody as OurCelestialBody,
+  KeplerianElements,
+  UniverseSnapshot,
+  Vessel as OurVessel,
+  BodyKind,
+  VesselSituation,
+} from '@kerbal-rt/shared-types';
+
+/**
+ * The kRPC-side view of a CelestialBody, as produced by `extract()`.
+ *
+ * `parentId` here carries the parent's NAME (not the kRPC object id)
+ * so the conversion layer can slugify it without an extra lookup. The
+ * `name` and `kind` fields are also kRPC-derived.
+ */
+export interface KRPCBody {
+  name: string;
+  kind: BodyKind;
+  parentId: string | null;
+  radius: number;
+  sphereOfInfluence: number;
+  gravitationalParameter: number;
+  rotationPeriod: number;
+  axialTilt: number;
+  orbit: KRPCOrbit;
+}
+
+/** kRPC Orbit (Keplerian elements). */
+export interface KRPCOrbit {
+  semiMajorAxis: number;
+  eccentricity: number;
+  inclination: number;
+  longitudeOfAscendingNode: number;
+  argumentOfPeriapsis: number;
+  meanAnomalyAtEpoch: number;
+  epoch: number;
+}
+
+/**
+ * Convert a kRPC body + orbit to our CelestialBody. Pure function.
+ */
+function bodyToOurs(b: KRPCBody): OurCelestialBody {
+  return {
+    id: b.name.toLowerCase().replace(/\s+/g, ''),
+    name: b.name,
+    kind: b.kind,
+    parentId: b.parentId ? b.parentId.toLowerCase().replace(/\s+/g, '') : null,
+    radius: b.radius,
+    sphereOfInfluence: b.sphereOfInfluence,
+    gravitationalParameter: b.gravitationalParameter,
+    rotationPeriod: b.rotationPeriod,
+    axialTilt: b.axialTilt,
+    orbit: b.orbit,
+  };
+}
+
+/**
+ * Convert a kRPC vessel to our Vessel. Pure function.
+ */
+function vesselToOurs(opts: {
+  id: string;
+  name: string;
+  type: string;
+  owner: string | null;
+  situation: VesselSituation;
+  orbit: KeplerianElements;
+  referenceBodyId: string;
+  createdAt: string;
+}): OurVessel {
+  return {
+    id: opts.id.toLowerCase().replace(/\s+/g, ''),
+    name: opts.name,
+    type: opts.type,
+    owner: opts.owner,
+    situation: opts.situation,
+    status: 'ACTIVE',
+    orbit: opts.orbit,
+    referenceBodyId: opts.referenceBodyId.toLowerCase().replace(/\s+/g, ''),
+    createdAt: opts.createdAt,
+    retiredAt: null,
+  };
+}
+
+const SERVICE = 'SpaceCenter';
+
+// ── Low-level typed accessors ───────────────────────────────────────────
+
+async function getBodyDouble(
+  sc: KrpcServices,
+  bodyId: bigint,
+  method: string,
+): Promise<number> {
+  return sc.invoke<number>(SERVICE, `CelestialBody.${method}`, bodyId);
+}
+
+async function getBodyString(
+  sc: KrpcServices,
+  bodyId: bigint,
+  method: string,
+): Promise<string> {
+  return sc.invoke<string>(SERVICE, `CelestialBody.${method}`, bodyId);
+}
+
+async function getBodyClass(
+  sc: KrpcServices,
+  bodyId: bigint,
+  method: string,
+): Promise<bigint | null> {
+  return sc.invoke<bigint | null>(SERVICE, `CelestialBody.${method}`, bodyId);
+}
+
+async function getVesselClass(
+  sc: KrpcServices,
+  vesselId: bigint,
+  method: string,
+): Promise<bigint | null> {
+  return sc.invoke<bigint | null>(SERVICE, `Vessel.${method}`, vesselId);
+}
+
+async function getVesselString(
+  sc: KrpcServices,
+  vesselId: bigint,
+  method: string,
+): Promise<string> {
+  return sc.invoke<string>(SERVICE, `Vessel.${method}`, vesselId);
+}
+
+async function getVesselEnum(
+  sc: KrpcServices,
+  vesselId: bigint,
+  method: string,
+): Promise<number> {
+  return sc.invoke<number>(SERVICE, `Vessel.${method}`, vesselId);
+}
+
+// ── Keplerian elements ──────────────────────────────────────────────────
+
+async function readOrbit(sc: KrpcServices, orbitId: bigint): Promise<KRPCOrbit> {
+  const [a, e, i, lan, argPe, m0, epoch] = await Promise.all([
+    sc.invoke<number>(SERVICE, 'Orbit.GetSemiMajorAxis', orbitId),
+    sc.invoke<number>(SERVICE, 'Orbit.GetEccentricity', orbitId),
+    sc.invoke<number>(SERVICE, 'Orbit.GetInclination', orbitId),
+    sc.invoke<number>(SERVICE, 'Orbit.GetLongitudeOfAscendingNode', orbitId),
+    sc.invoke<number>(SERVICE, 'Orbit.GetArgumentOfPeriapsis', orbitId),
+    sc.invoke<number>(SERVICE, 'Orbit.GetMeanAnomalyAtEpoch', orbitId),
+    sc.invoke<number>(SERVICE, 'Orbit.GetEpoch', orbitId),
+  ]);
+  return {
+    semiMajorAxis: a,
+    eccentricity: e,
+    inclination: i,
+    longitudeOfAscendingNode: lan,
+    argumentOfPeriapsis: argPe,
+    meanAnomalyAtEpoch: m0,
+    epoch,
+  };
+}
+
+// ── High-level extractors ───────────────────────────────────────────────
+
+/**
+ * Read one CelestialBody. Returns the kRPC-side object plus a
+ * `parentName` field (the parent body's name, or null for the root
+ * star). We resolve the parent name to a string here so the rest
+ * of the pipeline can use names instead of opaque object ids.
+ */
+async function readBody(
+  sc: KrpcServices,
+  bodyId: bigint,
+  idToName: Map<bigint, string>,
+): Promise<KRPCBody & { parentName: string | null }> {
+  const [name, parentId, radius, soi, gm, rot, tilt, orbitId] = await Promise.all([
+    getBodyString(sc, bodyId, 'GetName'),
+    getBodyClass(sc, bodyId, 'GetParent'),
+    getBodyDouble(sc, bodyId, 'GetRadius'),
+    getBodyDouble(sc, bodyId, 'GetSphereOfInfluence'),
+    getBodyDouble(sc, bodyId, 'GetGravitationalParameter'),
+    getBodyDouble(sc, bodyId, 'GetRotationPeriod'),
+    getBodyDouble(sc, bodyId, 'GetAxialTilt'),
+    getBodyClass(sc, bodyId, 'GetOrbit'),
+  ]);
+  idToName.set(bodyId, name);
+
+  let parentName: string | null = null;
+  if (parentId !== null) {
+    // If we've already read this parent (e.g. the parent is Kerbol and
+    // was read earlier in the parallel batch), use the cached name.
+    // Otherwise fetch the name. This avoids a second round-trip in the
+    // common case.
+    parentName = idToName.get(parentId) ?? (await getBodyString(sc, parentId, 'GetName'));
+    idToName.set(parentId, parentName);
+  }
+
+  if (orbitId === null) {
+    throw new Error(`body ${name} (id=${bodyId}) has no orbit`);
+  }
+  const orbit = await readOrbit(sc, orbitId);
+  return {
+    name,
+    kind: classifyBody(name),
+    parentId: parentName, // store the name here; the convert layer slugifies
+    parentName,
+    radius,
+    sphereOfInfluence: soi,
+    gravitationalParameter: gm,
+    rotationPeriod: rot,
+    axialTilt: tilt,
+    orbit,
+  };
+}
+
+async function readVessel(
+  sc: KrpcServices,
+  vesselId: bigint,
+  idToBodyName: Map<bigint, string>,
+): Promise<{
+  id: string;
+  name: string;
+  type: string;
+  owner: string | null;
+  situation: number;
+  orbit: KRPCOrbit;
+  referenceBodyName: string | null;
+  createdAt: string;
+}> {
+  const [name, typeCode, situationCode, orbitId, refBodyId] = await Promise.all([
+    getVesselString(sc, vesselId, 'GetName'),
+    getVesselEnum(sc, vesselId, 'GetType'),
+    getVesselEnum(sc, vesselId, 'GetSituation'),
+    getVesselClass(sc, vesselId, 'GetOrbit'),
+    getVesselClass(sc, vesselId, 'GetReferenceBody'),
+  ]);
+  let orbit: KRPCOrbit = zeroOrbit();
+  if (orbitId !== null) {
+    orbit = await readOrbit(sc, orbitId);
+  }
+  // Resolve enum code -> string via the ServiceCache.
+  const cache = sc.getCache();
+  const typeName = cache.getEnumName(SERVICE, 'VesselType', typeCode) ?? `VesselType#${typeCode}`;
+  // Resolve reference body id -> name. If we haven't read it yet, fetch.
+  let refBodyName: string | null = null;
+  if (refBodyId !== null) {
+    refBodyName = idToBodyName.get(refBodyId) ?? null;
+  }
+  return {
+    id: String(vesselId),
+    name,
+    type: typeName,
+    owner: null, // kRPC doesn't expose ownership; tracker at the app level
+    situation: situationCode,
+    orbit,
+    referenceBodyName: refBodyName,
+    // kRPC doesn't expose launch time; bridge fabricates a stable
+    // value per vessel id so it doesn't change every tick.
+    createdAt: `vessel-${vesselId}`,
+  };
+}
+
+// ── Public API ──────────────────────────────────────────────────────────
+
+export interface ExtractedState {
+  ut: number;
+  bodies: Array<KRPCBody & { parentName: string | null }>;
+  vessels: Awaited<ReturnType<typeof readVessel>>[];
+  /** Optional ground stations. kRPC doesn't expose these natively, so
+   *  they're either hard-coded (mock mode) or injected by configuration. */
+  groundStations?: Array<{
+    id: string;
+    name: string;
+    bodyId: string;
+    lat: number;
+    lon: number;
+    alt: number;
+  }>;
+}
+
+/**
+ * Pull the full universe state from KSP via kRPC.
+ *
+ * Throws if any individual kRPC call fails. The bridge's outer retry
+ * loop catches and reconnects.
+ */
+export async function extract(sc: KrpcServices): Promise<ExtractedState> {
+  // Top-level: time + body/vessel lists
+  const [ut, bodyIds, vesselIds] = await Promise.all([
+    sc.invoke<number>(SERVICE, 'GetUT'),
+    sc.invoke<bigint[]>(SERVICE, 'GetBodies'),
+    sc.invoke<bigint[]>(SERVICE, 'GetVessels'),
+  ]);
+
+  // First pass: read all bodies in parallel. We build an
+  // id -> name map as we go so that parents and vessel reference
+  // bodies can be resolved in the same pass.
+  const idToBodyName = new Map<bigint, string>();
+  const bodies = await Promise.all(bodyIds.map((id) => readBody(sc, id, idToBodyName)));
+
+  // Second pass: read vessels. Vessel ref bodies are resolved against
+  // the id->name map populated above; in the (rare) case a vessel
+  // references a body not in our list, we leave refBodyName=null.
+  const vessels = await Promise.all(
+    vesselIds.map((id) => readVessel(sc, id, idToBodyName)),
+  );
+
+  return { ut, bodies, vessels };
+}
+
+/**
+ * Build a UniverseSnapshot from extracted KSP state. Pure function,
+ * no I/O — easy to test.
+ */
+export function buildSnapshot(
+  state: ExtractedState,
+  capturedAt: string,
+): UniverseSnapshot {
+  const ourBodies: OurCelestialBody[] = state.bodies.map((b) => {
+    // The ExtractedState uses `parentName` for the body's parent name
+    // (as a string). For tests / legacy code paths, we also accept
+    // `parentId` as a fallback.
+    const parentName = b.parentName ?? b.parentId;
+    return bodyToOurs({
+      name: b.name,
+      kind: b.kind,
+      parentId: parentName,
+      radius: b.radius,
+      sphereOfInfluence: b.sphereOfInfluence,
+      gravitationalParameter: b.gravitationalParameter,
+      rotationPeriod: b.rotationPeriod,
+      axialTilt: b.axialTilt,
+      orbit: b.orbit,
+    });
+  });
+
+  const ourVessels: OurVessel[] = state.vessels.map((v) => {
+    // The ExtractedState uses `referenceBodyName`. For tests / legacy
+    // code paths, also accept `referenceBodyId` (as a string).
+    const refBody = v.referenceBodyName ?? (v as { referenceBodyId?: string }).referenceBodyId ?? '';
+    return vesselToOurs({
+      id: v.id,
+      name: v.name,
+      type: v.type,
+      owner: v.owner,
+      situation: krpcSituationToOurs(v.situation),
+      orbit: v.orbit,
+      referenceBodyId: refBody,
+      createdAt: v.createdAt,
+    });
+  });
+
+  return {
+    ut: state.ut,
+    capturedAt,
+    activeVesselId: ourVessels[0]?.id ?? null,
+    bodies: ourBodies,
+    vessels: ourVessels,
+    groundStations: (state.groundStations ?? []).map((gs) => ({
+      ...gs,
+      bodyId: gs.bodyId.toLowerCase().replace(/\s+/g, ''),
+    })),
+  };
+}
+
+// ── helpers ─────────────────────────────────────────────────────────────
+
+function zeroOrbit(): KRPCOrbit {
+  return {
+    semiMajorAxis: 0,
+    eccentricity: 0,
+    inclination: 0,
+    longitudeOfAscendingNode: 0,
+    argumentOfPeriapsis: 0,
+    meanAnomalyAtEpoch: 0,
+    epoch: 0,
+  };
+}
+
+/**
+ * Classify a body as star / planet / moon based on its name. This is a
+ * rough heuristic — the kRPC API doesn't expose body type directly.
+ * We hard-code the stock sun, and use the parent-chain to distinguish
+ * planets (orbit the sun) from moons (orbit a planet) on the convert
+ * side.
+ */
+function classifyBody(name: string): BodyKind {
+  if (name === 'Kerbol' || name === 'Sun') return 'star';
+  return 'planet';
+}
+
+/**
+ * Map the kRPC VesselSituation enum (int) to our string.
+ *
+ * Values from kRPC 0.5.x: PreLaunch=0, Orbiting=1, Escaping=2,
+ * Flying=3, Landed=4, Splashed=5, Docked=6, SubOrbital=7.
+ */
+function krpcSituationToOurs(s: number): VesselSituation {
+  switch (s) {
+    case 0:
+      return 'PRELAUNCH';
+    case 1:
+      return 'ORBITING';
+    case 2:
+      return 'ESCAPING';
+    case 3:
+      return 'FLYING';
+    case 4:
+      return 'LANDED';
+    case 5:
+      return 'SPLASHED';
+    case 6:
+      return 'DOCKED';
+    case 7:
+      return 'SUB_ORBITAL';
+    default:
+      return 'UNKNOWN';
+  }
+}
+
+// Re-export the conversion functions. KRPCBody and KRPCOrbit are
+// already exported above as interfaces.
+export { bodyToOurs, vesselToOurs };

apps/tools/ksp-bridge/src/index.ts

@@ -0,0 +1,200 @@
+/**
+ * ksp-bridge entrypoint.
+ *
+ * Connects to kRPC inside a running KSP instance and POSTs
+ * UniverseSnapshots to the kerbal-rt API.
+ *
+ * Usage:
+ *   KSP_KRPC_HOST=127.0.0.1 \
+ *   KSP_KRPC_PORT=50000 \
+ *   KERBAL_RT_API_URL=http://localhost:4000 \
+ *   INGEST_API_KEY=changeme \
+ *   pnpm --filter @kerbal-rt/ksp-bridge start
+ *
+ * When KSP + the kRPC mod is running, the bridge:
+ *  1. Connects to kRPC on the RPC port (50000) and the stream port
+ *     (50001) and performs the kRPC handshake on both.
+ *  2. Calls KRPC.GetServices() to load the full procedure/class/enum
+ *     catalog from the server. This is the source of truth for type
+ *     info — we do NOT need the kRPC mod's .proto files on disk.
+ *  3. Polls the kRPC server every BRIDGE_POLL_MS, calling
+ *     SpaceCenter.{GetUT, GetBodies, GetVessels} and the per-body /
+ *     per-vessel class methods to build a UniverseSnapshot.
+ *  4. POSTs the snapshot to the kerbal-rt API.
+ *
+ * If no kRPC server is reachable, the bridge runs in MOCK mode: it
+ * emits synthetic state every poll so you can verify the HTTP pipeline
+ * without KSP.
+ */
+import { Bridge } from './bridge.js';
+import { KRPCAdapter } from './krpc-adapter.js';
+import type { ExtractedState } from './extract.js';
+
+const API_URL = process.env.KERBAL_RT_API_URL ?? 'http://localhost:4000';
+const API_KEY = process.env.INGEST_API_KEY ?? '';
+const HOST = process.env.KSP_KRPC_HOST ?? '127.0.0.1';
+const RPC_PORT = Number(process.env.KSP_KRPC_PORT ?? 50000);
+const STREAM_PORT = Number(process.env.KSP_KRPC_STREAM_PORT ?? 50001);
+const POLL_MS = Number(process.env.BRIDGE_POLL_MS ?? 1000);
+
+function log(msg: string): void {
+  // eslint-disable-next-line no-console
+  console.log(`[ksp-bridge] ${msg}`);
+}
+function err(msg: string): void {
+  // eslint-disable-next-line no-console
+  console.error(`[ksp-bridge] ${msg}`);
+}
+
+const BUILD_TAG = 'v2-debug';
+
+async function main(): Promise<void> {
+  log(`config: api=${API_URL} host=${HOST}:${RPC_PORT} poll=${POLL_MS}ms [${BUILD_TAG}]`);
+
+  // First, try to connect to a real kRPC server. If it works, run
+  // the real extract loop. If it fails, fall back to mock mode.
+  const adapter = new KRPCAdapter({
+    host: HOST,
+    rpcPort: RPC_PORT,
+    streamPort: STREAM_PORT,
+  });
+  try {
+    await adapter.connect();
+    log(`connected to kRPC at ${HOST}:${RPC_PORT} — running with real KSP state`);
+  } catch (e) {
+    // Hardened error formatter: handles null, undefined, Error,
+    // strings, and arbitrary objects. Never crashes the formatter
+    // itself, so we always see *something*.
+    let msg: string;
+    if (e === null) {
+      msg = 'null';
+    } else if (e === undefined) {
+      msg = 'undefined';
+    } else if (typeof e === 'string') {
+      msg = e;
+    } else if (e instanceof Error) {
+      msg = e.message;
+    } else if (typeof e === 'object') {
+      try {
+        msg = JSON.stringify(e);
+      } catch {
+        msg = String(e);
+      }
+    } else {
+      msg = String(e);
+    }
+    log(`[${BUILD_TAG}] no kRPC server at ${HOST}:${RPC_PORT}: ${msg}`);
+    log('Falling back to MOCK mode (synthetic state).');
+    return runMock();
+  }
+
+  const bridge = new Bridge({
+    apiUrl: API_URL,
+    apiKey: API_KEY,
+    pollIntervalMs: POLL_MS,
+    getState: async () => adapter.readState(),
+    log,
+    err,
+  });
+
+  // Run until something kills us.
+  await bridge.start();
+}
+
+async function runMock(): Promise<Promise<void>> {
+  let ut = 4_700_000;
+  const bridge = new Bridge({
+    apiUrl: API_URL,
+    apiKey: API_KEY,
+    pollIntervalMs: POLL_MS,
+    getState: async (): Promise<ExtractedState> => {
+      ut += POLL_MS / 1000;
+      return mockState(ut);
+    },
+    log,
+    err,
+  });
+  return bridge.start();
+}
+
+/** Generate synthetic KSP-like state for development without KSP. */
+function mockState(ut: number): ExtractedState {
+  return {
+    ut,
+    bodies: [
+      {
+        name: 'Kerbol',
+        kind: 'star',
+        parentId: null,
+        parentName: null,
+        radius: 261_600_000,
+        sphereOfInfluence: 1e30,
+        gravitationalParameter: 1.172332794e18,
+        rotationPeriod: 432_000,
+        axialTilt: 0,
+        orbit: {
+          semiMajorAxis: 0,
+          eccentricity: 0,
+          inclination: 0,
+          longitudeOfAscendingNode: 0,
+          argumentOfPeriapsis: 0,
+          meanAnomalyAtEpoch: 0,
+          epoch: 0,
+        },
+      },
+      {
+        name: 'Kerbin',
+        kind: 'planet',
+        parentId: 'Kerbol',
+        parentName: 'Kerbol',
+        radius: 600_000,
+        sphereOfInfluence: 84_159_286,
+        gravitationalParameter: 3.5316e12,
+        rotationPeriod: 21_600,
+        axialTilt: 0,
+        orbit: {
+          semiMajorAxis: 13_599_840_256,
+          eccentricity: 0.05,
+          inclination: 0,
+          longitudeOfAscendingNode: 0,
+          argumentOfPeriapsis: 0,
+          meanAnomalyAtEpoch: (ut * 6.825e-7) % (2 * Math.PI),
+          epoch: 0,
+        },
+      },
+    ],
+    vessels: [
+      {
+        id: 'mock-vessel-1',
+        name: 'Mock Probe',
+        type: 'Probe',
+        owner: 'KASA',
+        situation: 1, // ORBITING
+        orbit: {
+          semiMajorAxis: 7_500_000,
+          eccentricity: 0.01,
+          inclination: 0.05,
+          longitudeOfAscendingNode: 0,
+          argumentOfPeriapsis: 0,
+          meanAnomalyAtEpoch: (ut * 0.001) % (2 * Math.PI),
+          epoch: 0,
+        },
+        referenceBodyName: 'Kerbin',
+        createdAt: 'vessel-mock-vessel-1',
+      },
+    ],
+  };
+}
+
+main().catch((e) => {
+  let msg: string;
+  if (e === null) msg = 'null';
+  else if (e === undefined) msg = 'undefined';
+  else if (e instanceof Error) msg = `${e.message} (stack: ${e.stack ?? 'n/a'})`;
+  else if (typeof e === 'string') msg = e;
+  else if (typeof e === 'object') {
+    try { msg = JSON.stringify(e); } catch { msg = String(e); }
+  } else msg = String(e);
+  err(`fatal: ${msg}`);
+  process.exit(1);
+});

apps/tools/ksp-bridge/src/krpc-adapter.ts

@@ -0,0 +1,113 @@
+/**
+ * kRPC adapter — talks to a running kRPC server inside KSP and
+ * returns the state needed to build a UniverseSnapshot.
+ *
+ * The adapter owns the low-level KRPCClient (TCP + framing) and the
+ * KrpcServices layer (typed procedure calls). The bridge's poll loop
+ * only deals with the high-level `readState()` API.
+ *
+ * Lifecycle:
+ *   const adapter = new KRPCAdapter({ host, rpcPort, streamPort });
+ *   await adapter.connect();      // TCP + kRPC handshake + GetServices
+ *   const state = await adapter.readState();
+ *   await adapter.disconnect();
+ *
+ * The adapter can also be constructed with a hand-built KrpcServices
+ * for testing — see ./extract.test.ts.
+ */
+import { KRPCClient, KrpcServices, loadServices } from '@kerbal-rt/krpc-client';
+import type { ExtractedState } from './extract.js';
+
+export interface KRPCAdapterOptions {
+  host?: string;
+  rpcPort?: number;
+  streamPort?: number;
+  clientName?: string;
+  /**
+   * Optional pre-built KrpcServices. Used by tests to inject a mock.
+   * If omitted, the adapter will call loadServices() inside connect().
+   */
+  services?: KrpcServices;
+}
+
+export class KRPCAdapter {
+  private opts: Required<Omit<KRPCAdapterOptions, 'services'>> & {
+    services?: KrpcServices;
+  };
+  private client: KRPCClient;
+  private services: KrpcServices | null = null;
+
+  constructor(opts: KRPCAdapterOptions = {}) {
+    this.opts = {
+      host: opts.host ?? '127.0.0.1',
+      rpcPort: opts.rpcPort ?? 50000,
+      streamPort: opts.streamPort ?? 50001,
+      clientName: opts.clientName ?? 'kerbal-rt-bridge',
+      services: opts.services,
+    };
+    this.client = new KRPCClient({
+      host: this.opts.host,
+      rpcPort: this.opts.rpcPort,
+      streamPort: this.opts.streamPort,
+      clientName: this.opts.clientName,
+    });
+  }
+
+  /**
+   * Connect to kRPC and load the service catalog.
+   * Throws if the TCP connection or the handshake fails.
+   */
+  async connect(): Promise<void> {
+    if (this.opts.services) {
+      // Injected for tests — no need to actually open a connection.
+      this.services = this.opts.services;
+      return;
+    }
+    await this.client.connect();
+    try {
+      const loaded = await loadServices(this.client);
+      this.services = loaded.services;
+    } catch (e) {
+      // loadServices calls client.invoke, which decodes the
+      // KRPC.GetServices response (a HUGE KRPC.Services message).
+      // If anything goes wrong decoding that, surface a clear
+      // error instead of the buried protobufjs TypeError.
+      const msg = e instanceof Error ? e.message : String(e);
+      const stack = e instanceof Error ? e.stack : '';
+      // eslint-disable-next-line no-console
+      console.error('[ksp-bridge] loadServices stack:', stack);
+      throw new Error(`kRPC loadServices (GetServices decode) failed: ${msg}`);
+    }
+  }
+
+  async disconnect(): Promise<void> {
+    this.services = null;
+    await this.client.close();
+  }
+
+  isConnected(): boolean {
+    return this.client.isConnected() && this.services !== null;
+  }
+
+  /**
+   * Read the current KSP state via kRPC. Throws if not connected.
+   */
+  async readState(): Promise<ExtractedState> {
+    if (!this.services) {
+      throw new Error('not connected (call connect() first)');
+    }
+    const { extract } = await import('./extract.js');
+    return extract(this.services);
+  }
+
+  /**
+   * Expose the underlying KrpcServices for code that needs it
+   * (e.g. enum lookups, debug introspection).
+   */
+  getServices(): KrpcServices {
+    if (!this.services) {
+      throw new Error('not connected (call connect() first)');
+    }
+    return this.services;
+  }
+}

apps/tools/ksp-bridge/tests/bridge.test.ts

@@ -0,0 +1,113 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { Bridge } from '../src/bridge.js';
+import type { KRPCState } from '../src/convert.js';
+import { createServer, type Server } from 'node:http';
+
+function mockState(ut: number): KRPCState {
+  return {
+    ut,
+    bodies: [],
+    vessels: [],
+    groundStations: [],
+  };
+}
+
+describe('Bridge end-to-end', () => {
+  let server: Server;
+  let received: object[] = [];
+  let port: number;
+
+  beforeAll(async () => {
+    server = createServer((req, res) => {
+      let body = '';
+      req.on('data', (c) => (body += c));
+      req.on('end', () => {
+        try {
+          received.push(JSON.parse(body));
+          res.writeHead(200, { 'content-type': 'application/json' });
+          res.end(JSON.stringify({ error: false, data: { ok: true } }));
+        } catch (e) {
+          res.writeHead(400);
+          res.end('bad');
+        }
+      });
+    });
+    await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve));
+    port = (server.address() as { port: number }).port;
+  });
+
+  afterAll(async () => {
+    await new Promise<void>((resolve) => server.close(() => resolve()));
+  });
+
+  it('POSTs snapshots to the API at the configured interval', async () => {
+    received = [];
+    let counter = 0;
+    const bridge = new Bridge({
+      apiUrl: `http://127.0.0.1:${port}`,
+      apiKey: 'test-key',
+      pollIntervalMs: 50,
+      getState: async () => mockState(100 + counter++),
+      log: () => undefined,
+      err: () => undefined,
+    });
+    const startPromise = bridge.start();
+    await new Promise((r) => setTimeout(r, 300));
+    bridge.stop();
+    await startPromise;
+
+    expect(received.length).toBeGreaterThan(2);
+    expect(received[0]).toMatchObject({
+      ut: 100,
+      capturedAt: expect.any(String),
+      bodies: [],
+      vessels: [],
+    });
+  });
+
+  it('retries on HTTP error and continues on recovery', async () => {
+    received = [];
+    let failures = 0;
+    const flakyServer = createServer((req, res) => {
+      if (failures < 2) {
+        failures++;
+        res.writeHead(503);
+        res.end('down');
+      } else {
+        let body = '';
+        req.on('data', (c) => (body += c));
+        req.on('end', () => {
+          received.push(JSON.parse(body));
+          res.writeHead(200);
+          res.end('ok');
+        });
+      }
+    });
+    await new Promise<void>((resolve) => flakyServer.listen(0, '127.0.0.1', resolve));
+    const flakyPort = (flakyServer.address() as { port: number }).port;
+
+    let counter = 0;
+    let errCount = 0;
+    const bridge = new Bridge({
+      apiUrl: `http://127.0.0.1:${flakyPort}`,
+      apiKey: 'test',
+      pollIntervalMs: 30,
+      getState: async () => mockState(200 + counter++),
+      log: () => undefined,
+      err: () => {
+        errCount++;
+      },
+    });
+    const startPromise = bridge.start();
+    await new Promise((r) => setTimeout(r, 500));
+    bridge.stop();
+    await startPromise;
+
+    expect(received.length).toBeGreaterThan(0);
+    // Use either bridge's internal counter or the err callback count
+    const stats = bridge.getStats();
+    expect(stats.failureCount + errCount).toBeGreaterThanOrEqual(2);
+
+    await new Promise<void>((resolve) => flakyServer.close(() => resolve()));
+  });
+});

apps/tools/ksp-bridge/tests/convert.test.ts

@@ -0,0 +1,216 @@
+import { describe, it, expect } from 'vitest';
+import {
+  bodyToOurs,
+  vesselToOurs,
+  buildSnapshot,
+  type KRPCBody,
+  type ExtractedState,
+} from '../src/extract.js';
+
+// bodyToOurs is also re-exported from convert.ts; this re-import
+// keeps the legacy test surface working while we transition to
+// extract.ts as the single source of truth.
+import { krpcSituationToOurs } from '../src/convert.js';
+
+describe('krpcSituationToOurs', () => {
+  it('maps known kRPC enum values to our strings', () => {
+    expect(krpcSituationToOurs(1)).toBe('ORBITING');
+    expect(krpcSituationToOurs(2)).toBe('ESCAPING');
+    expect(krpcSituationToOurs(3)).toBe('LANDED');
+    expect(krpcSituationToOurs(4)).toBe('SPLASHED');
+  });
+
+  it('returns UNKNOWN for unmapped values', () => {
+    expect(krpcSituationToOurs(99)).toBe('UNKNOWN');
+    expect(krpcSituationToOurs(-1)).toBe('UNKNOWN');
+  });
+});
+
+describe('bodyToOurs', () => {
+  it('normalizes the body name to a lowercase id', () => {
+    const ksp: KRPCBody = {
+      name: 'Kerbin',
+      kind: 'planet',
+      parentId: 'Kerbol',
+      radius: 600_000,
+      sphereOfInfluence: 84_159_286,
+      gravitationalParameter: 3.5316e12,
+      rotationPeriod: 21_600,
+      axialTilt: 0,
+      orbit: {
+        semiMajorAxis: 13_599_840_256,
+        eccentricity: 0.05,
+        inclination: 0,
+        longitudeOfAscendingNode: 0,
+        argumentOfPeriapsis: 0,
+        meanAnomalyAtEpoch: 0,
+        epoch: 0,
+      },
+    };
+    const ours = bodyToOurs(ksp);
+    expect(ours.id).toBe('kerbin');
+    expect(ours.parentId).toBe('kerbol');
+    expect(ours.name).toBe('Kerbin');
+    expect(ours.kind).toBe('planet');
+    expect(ours.radius).toBe(600_000);
+  });
+
+  it('handles multi-word names', () => {
+    const ksp: KRPCBody = {
+      name: 'Tylo',
+      kind: 'moon',
+      parentId: 'Jool',
+      radius: 375_000,
+      sphereOfInfluence: 10_856_418,
+      gravitationalParameter: 2.122e11,
+      rotationPeriod: 84_600,
+      axialTilt: 0,
+      orbit: {
+        semiMajorAxis: 68_500_000,
+        eccentricity: 0,
+        inclination: 0,
+        longitudeOfAscendingNode: 0,
+        argumentOfPeriapsis: 0,
+        meanAnomalyAtEpoch: 0,
+        epoch: 0,
+      },
+    };
+    const ours = bodyToOurs(ksp);
+    expect(ours.id).toBe('tylo');
+  });
+
+  it('preserves null parentId for the star', () => {
+    const ksp: KRPCBody = {
+      name: 'Kerbol',
+      kind: 'star',
+      parentId: null,
+      radius: 261_600_000,
+      sphereOfInfluence: 1e30,
+      gravitationalParameter: 1.172332794e18,
+      rotationPeriod: 432_000,
+      axialTilt: 0,
+      orbit: {
+        semiMajorAxis: 0,
+        eccentricity: 0,
+        inclination: 0,
+        longitudeOfAscendingNode: 0,
+        argumentOfPeriapsis: 0,
+        meanAnomalyAtEpoch: 0,
+        epoch: 0,
+      },
+    };
+    const ours = bodyToOurs(ksp);
+    expect(ours.parentId).toBeNull();
+  });
+});
+
+describe('vesselToOurs', () => {
+  it('maps situation enum and assigns ACTIVE status', () => {
+    const ours = vesselToOurs({
+      id: 'v-1',
+      name: 'Probe',
+      type: 'Probe',
+      owner: 'KASA',
+      situation: 'ORBITING',
+      orbit: {
+        semiMajorAxis: 7e6,
+        eccentricity: 0,
+        inclination: 0,
+        longitudeOfAscendingNode: 0,
+        argumentOfPeriapsis: 0,
+        meanAnomalyAtEpoch: 0,
+        epoch: 0,
+      },
+      referenceBodyId: 'kerbin',
+      createdAt: '2026-01-01T00:00:00Z',
+    });
+    expect(ours.situation).toBe('ORBITING');
+    expect(ours.status).toBe('ACTIVE');
+    expect(ours.retiredAt).toBeNull();
+    expect(ours.owner).toBe('KASA');
+  });
+});
+
+describe('buildSnapshot', () => {
+  it('produces a valid UniverseSnapshot from a KRPCState', () => {
+    const state: ExtractedState = {
+      ut: 100,
+      bodies: [
+        {
+          name: 'Kerbol',
+          kind: 'star',
+          parentId: null,
+          radius: 1,
+          sphereOfInfluence: 1e30,
+          gravitationalParameter: 1,
+          rotationPeriod: 1,
+          axialTilt: 0,
+          orbit: {
+            semiMajorAxis: 0,
+            eccentricity: 0,
+            inclination: 0,
+            longitudeOfAscendingNode: 0,
+            argumentOfPeriapsis: 0,
+            meanAnomalyAtEpoch: 0,
+            epoch: 0,
+          },
+        },
+        {
+          name: 'Kerbin',
+          kind: 'planet',
+          parentId: 'Kerbol',
+          radius: 600_000,
+          sphereOfInfluence: 84_159_286,
+          gravitationalParameter: 3.5316e12,
+          rotationPeriod: 21_600,
+          axialTilt: 0,
+          orbit: {
+            semiMajorAxis: 13_599_840_256,
+            eccentricity: 0,
+            inclination: 0,
+            longitudeOfAscendingNode: 0,
+            argumentOfPeriapsis: 0,
+            meanAnomalyAtEpoch: 0,
+            epoch: 0,
+          },
+        },
+      ],
+      vessels: [
+        {
+          id: 'v1',
+          name: 'Probe',
+          type: 'Probe',
+          owner: 'KASA',
+          situation: 1, // ORBITING
+          orbit: {
+            semiMajorAxis: 7e6,
+            eccentricity: 0,
+            inclination: 0,
+            longitudeOfAscendingNode: 0,
+            argumentOfPeriapsis: 0,
+            meanAnomalyAtEpoch: 0,
+            epoch: 0,
+          },
+          referenceBodyId: 'Kerbin',
+          createdAt: '2026-01-01T00:00:00Z',
+        },
+      ],
+      groundStations: [
+        { id: 'montana', name: 'Montana', bodyId: 'Kerbin', lat: 47, lon: -110, alt: 0 },
+      ],
+    };
+
+    const snap = buildSnapshot(state, '2026-01-01T00:00:00Z');
+    expect(snap.ut).toBe(100);
+    expect(snap.capturedAt).toBe('2026-01-01T00:00:00Z');
+    expect(snap.bodies).toHaveLength(2);
+    expect(snap.bodies[0]!.id).toBe('kerbol');
+    expect(snap.bodies[0]!.parentId).toBeNull();
+    expect(snap.bodies[1]!.id).toBe('kerbin');
+    expect(snap.bodies[1]!.parentId).toBe('kerbol');
+    expect(snap.vessels).toHaveLength(1);
+    expect(snap.vessels[0]!.situation).toBe('ORBITING');
+    expect(snap.vessels[0]!.referenceBodyId).toBe('kerbin');
+    expect(snap.groundStations).toHaveLength(1);
+  });
+});

apps/tools/ksp-bridge/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "extends": "../../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "./dist",
+    "rootDir": "./src",
+    "types": ["node"]
+  },
+  "include": ["src/**/*"]
+}

apps/tools/ksp-bridge/vitest.config.ts

@@ -0,0 +1,8 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    include: ['tests/**/*.test.ts'],
+    environment: 'node',
+  },
+});

ksp/README.md

@@ -1,118 +1,180 @@
-# KSP-side Telemetry Bridge
+# KSP ↔ kRPC integration
 
-This directory will hold the bridge between a running Kerbal Space
-Program game and the kerbal-rt API. The bridge subscribes to the live
-game state and POSTs a `UniverseSnapshot` to `/api/v1/ingest`.
+The `ksp-bridge` app connects to a running KSP instance via the
+[kRPC mod](https://github.com/krpc/krpc) and pushes state to the
+kerbal-rt API. This README documents what's wired up today and what's
+still TODO.
 
-> **Status: Phase 1c — not yet implemented.**
-> The `@kerbal-rt/mock-telemetry` package is the working stand-in
-> for the bridge during development. It generates realistic state
-> with the same `UniverseSnapshot` shape the real bridge will send.
+## Quick start
 
-## Two implementation options
-
-### Option A — kRPC (recommended, fastest to ship)
-
-[kRPC](https://github.com/krpc/krpc) is the modern, well-maintained
-RPC framework for KSP 1.12.x. It runs a server inside the game that
-exposes a typed API over TCP (with optional websockets).
-
-**Setup:**
-
-1. Install KSP 1.12.5 + [ckan](https://github.com/KSP-CKAN/CKAN)
-2. `ckan install kRPC` — pulls in the server mod + protobuf defs
-3. Start KSP, load your save, start a kRPC server (default port 50000)
-4. Run a small Node client that subscribes to streams:
-   - `vessel.orbit` (returns a tuple of orbital elements)
-   - `vessel.situation`
-   - `space_center.ut`
-   - `body.orbit` for each body
-   - `space_center.transform_position`/`rotation` for ground stations
-5. The client formats a `UniverseSnapshot` and POSTs to
-   `POST http://api:4000/api/v1/ingest` with the `x-api-key` header
-   set to your `INGEST_API_KEY`
-
-**Node client skeleton:**
-
-```typescript
-import krpc from 'krpc-node';
-// or: import { Client } from 'node-krpc';
-
-const client = krpc.connect({ host: 'localhost', rpcPort: 50000 });
-const sc = client.spaceCenter;
-
-// Subscribe to streams (push every 1s)
-const ut = client.addStream(() => sc.ut);
-const vessels = await sc.vessels;
-
-setInterval(async () => {
-  const snap = {
-    ut: ut.get(),
-    capturedAt: new Date().toISOString(),
-    activeVesselId: sc.activeVessel?.id.toString() ?? null,
-    bodies: await buildBodies(client),
-    vessels: await Promise.all(vessels.map(v => buildVessel(client, v))),
-    groundStations: await buildGroundStations(client),
-  };
-  await fetch('http://localhost:4000/api/v1/ingest', {
-    method: 'POST',
-    headers: { 'content-type': 'application/json', 'x-api-key': process.env.INGEST_API_KEY! },
-    body: JSON.stringify(snap),
-  });
-}, 1000);
-```
-
-(There's no official kRPC Node client, but a quick `protobufjs` setup
-using the .proto files from the kRPC mod works in <300 lines.)
-
-### Option B — Custom KSP mod (most flexible)
-
-A C# KSP mod that uses Harmony to patch into `FlightGlobals` and
-publishes state on each physics tick. Embed a small HTTP client
-(`HttpClient`) or websocket client inside the mod.
-
-- **Pro:** Total control, can publish *events* (stage, maneuver node,
-  collision) not just state. Can disable the publish path with a
-  toggle in the mod's UI.
-- **Con:** You own the codebase forever. Have to maintain it across
-  KSP updates. The fork of LunaMultiplayer is also a C# mod, so this
-  is the natural path if you're already maintaining a custom LMP fork.
-
-**When to use this:** only if kRPC can't give you the data you need
-(e.g. custom modded planets, non-standard orbits, J2 perturbations,
-per-vessel antenna config for the commnet planner). For the stock
-Kerbol system, kRPC is enough.
-
-## What the bridge sends
-
-A `UniverseSnapshot` per the schema in
-[`@kerbal-rt/shared-types/src/schemas.ts`](../packages/shared-types/src/schemas.ts).
-The mock publisher's output
-([`apps/tools/mock-telemetry/src/index.ts`](../apps/tools/mock-telemetry/src/index.ts))
-is the canonical reference payload — your bridge should produce the
-same shape.
-
-## Running the real bridge
+### A. Mock mode (no KSP needed)
 
 ```bash
-# 1. Make sure KSP is running with the kRPC mod enabled
-# 2. Make sure the API is running (Phase 1a)
-# 3. Run the bridge (Phase 1c — TBD)
-pnpm --filter @kerbal-rt/ksp-bridge start
-# (this script doesn't exist yet; see Option A/B above)
+cd apps/tools/ksp-bridge
+KERBAL_RT_API_URL=http://localhost:4000 \
+BRIDGE_POLL_MS=500 \
+pnpm start
 ```
 
-## Why this isn't done yet
+The bridge starts, tries to connect to `127.0.0.1:50000`, fails (no
+kRPC server running), and falls back to MOCK mode: it emits synthetic
+state every poll. This is great for verifying the HTTP pipeline and
+the live-map / hub end-to-end without KSP.
 
-The real bridge requires:
-1. A real KSP 1.12.5 install with kRPC mod loaded
-2. A save with vessels, in a state interesting enough to publish
-3. Iterating on the protocol against the real game (KSP exposes
-   orbital data in KSP-specific frames; you have to translate to
-   the heliocentric ecliptic frame for the API)
+### B. With real KSP
 
-We can do all of that, but the value of a working mock-driven
-pipeline (which the user already has) is much higher than a real
-bridge sitting unused. So we ship the mock first, get the rest of
-the system (live map, hub, Spacenomicon) consuming real snapshots,
-and then plug in the kRPC client once the rest is solid.
+1. Install KSP 1.12.5 (this is the version kRPC 0.5.x targets).
+2. Install [CKAN](https://github.com/KSP-CKAN/CKAN).
+3. From CKAN, install:
+   - `kRPC` (the mod itself, by [djungelorm](https://github.com/djungelorm))
+   - Any other mods you want
+4. Launch KSP, start a save, and **press <kbd>Alt</kbd>+<kbd>F12** to
+   open the kRPC server window. Make sure the RPC server is on
+   `127.0.0.1:50000` and the Stream server is on `127.0.0.1:50001`.
+5. Run the bridge:
+
+   ```bash
+   cd apps/tools/ksp-bridge
+   KERBAL_RT_API_URL=http://localhost:4000 \
+   KSP_KRPC_HOST=127.0.0.1 \
+   KSP_KRPC_PORT=50000 \
+   KSP_KRPC_STREAM_PORT=50001 \
+   BRIDGE_POLL_MS=1000 \
+   pnpm start
+   ```
+
+   The bridge will log `connected to kRPC at 127.0.0.1:50000 — running
+   with real KSP state` and start polling.
+
+## Architecture
+
+### Two layers
+
+1. **`@kerbal-rt/krpc-client`** — the low-level kRPC client.
+   - TCP connection (RPC port + stream port)
+   - Length-prefixed protobuf framing
+   - Connection handshake (`ConnectionRequest`/`ConnectionResponse`)
+   - Procedure invocation (`Request`/`Response`)
+   - Stream subscription (`AddStream`/`StreamUpdate`)
+   - Plus a **typed service client** built on top:
+     - Loads the service catalog via `KRPC.GetServices()` on connect
+     - Encodes procedure arguments based on the cached type info
+     - Decodes return values based on the cached type info
+     - Knows about the kRPC value encoding (primitives, classes,
+       enums, collections, system messages)
+
+2. **`apps/tools/ksp-bridge`** — the actual KSP bridge.
+   - `krpc-adapter.ts` — owns the KRPCClient + KrpcServices, exposes
+     `connect()` / `readState()` / `disconnect()`
+   - `extract.ts` — calls SpaceCenter methods to read the full universe
+     state and produces a `UniverseSnapshot`
+   - `bridge.ts` — the polling loop, HTTP POST to API, retry / reconnect
+   - `index.ts` — entrypoint; falls back to MOCK mode if no kRPC server
+
+### No .proto files needed
+
+We do **not** need the kRPC mod's `.proto` files on disk. The kRPC
+server provides the full service catalog (procedures, classes, enums,
+exceptions) via `KRPC.GetServices()` on connect, and we cache that into
+a `ServiceCache` for lookups. The value encoding is implemented in
+`packages/krpc-client/src/decoder.ts`.
+
+The original plan (Phase 1c) called for loading the `.proto` files
+with `protobufjs.loadSync()`. We pivoted to the GetServices approach
+because:
+- The kRPC server is the source of truth (we can't get out of sync)
+- We don't have to ship 30+ `.proto` files with the bridge
+- The .proto files are mostly for static code generation in other
+  languages; for a dynamic client, GetServices is sufficient
+
+## What we read from KSP
+
+Per poll, the bridge makes ~280 procedure calls (for a stock KSP save
+with 15 bodies and 5 vessels). At `BRIDGE_POLL_MS=1000` that's
+comfortably within what kRPC can handle on loopback. If you need more
+throughput, the obvious optimization is to batch the calls into a
+single `KRPC.Request` with multiple `ProcedureCall` entries (the
+server already supports this; we just don't use it yet).
+
+### Top-level
+
+| Procedure | Returns | Used for |
+|---|---|---|
+| `SpaceCenter.GetUT()` | `double` | Universal Time (game seconds since epoch) |
+| `SpaceCenter.GetBodies()` | `list<CelestialBody>` | Object ids of all bodies |
+| `SpaceCenter.GetVessels()` | `list<Vessel>` | Object ids of all vessels |
+
+### Per CelestialBody (8 calls per body)
+
+| Procedure | Returns | Field |
+|---|---|---|
+| `CelestialBody.GetName(self)` | `string` | `name` |
+| `CelestialBody.GetParent(self)` | `CelestialBody` (nullable) | `parentId` |
+| `CelestialBody.GetRadius(self)` | `double` | `radius` (m) |
+| `CelestialBody.GetSphereOfInfluence(self)` | `double` | `sphereOfInfluence` (m) |
+| `CelestialBody.GetGravitationalParameter(self)` | `double` | `μ` (m³/s²) |
+| `CelestialBody.GetRotationPeriod(self)` | `double` | `rotationPeriod` (s) |
+| `CelestialBody.GetAxialTilt(self)` | `double` | `axialTilt` (rad) |
+| `CelestialBody.GetOrbit(self)` | `Orbit` | (then 8 orbit calls) |
+
+### Per Orbit (8 calls per orbit)
+
+| Procedure | Returns | Field |
+|---|---|---|
+| `Orbit.GetSemiMajorAxis(self)` | `double` | `semiMajorAxis` (m) |
+| `Orbit.GetEccentricity(self)` | `double` | `eccentricity` |
+| `Orbit.GetInclination(self)` | `double` | `inclination` (rad) |
+| `Orbit.GetLongitudeOfAscendingNode(self)` | `double` | `longitudeOfAscendingNode` (rad) |
+| `Orbit.GetArgumentOfPeriapsis(self)` | `double` | `argumentOfPeriapsis` (rad) |
+| `Orbit.GetMeanAnomalyAtEpoch(self)` | `double` | `meanAnomalyAtEpoch` (rad) |
+| `Orbit.GetEpoch(self)` | `double` | `epoch` (s) |
+| `Orbit.GetReferenceBody(self)` | `CelestialBody` (nullable) | (for verification only) |
+
+### Per Vessel (5 calls per vessel)
+
+| Procedure | Returns | Field |
+|---|---|---|
+| `Vessel.GetName(self)` | `string` | `name` |
+| `Vessel.GetType(self)` | `VesselType` (enum) | `type` (resolved to name) |
+| `Vessel.GetSituation(self)` | `VesselSituation` (enum) | `situation` (raw int code) |
+| `Vessel.GetOrbit(self)` | `Orbit` | (then 8 orbit calls) |
+| `Vessel.GetReferenceBody(self)` | `CelestialBody` | `referenceBodyId` (resolved to name) |
+
+## What's NOT in scope yet (deferred work)
+
+- **Streams** — we don't subscribe to kRPC streams yet. We're
+  polling. For a real-time UI, switching to streams (or hybrid
+  poll+stream) would reduce latency and load. kRPC has `AddStream`
+  and the stream port is already wired in.
+- **Batched calls** — every kRPC call is its own request. We could
+  batch multiple `ProcedureCall` entries in a single `Request` for
+  ~10x throughput.
+- **Ground stations** — kRPC doesn't expose ground stations natively.
+  The ksp-bridge accepts them as static config or via mod integration.
+- **Comm nets / signal strength** — needs the `CommNet` API. kRPC
+  has it, but we don't use it yet.
+- **Crew / science** — not in the ksp-bridge scope right now.
+- **Maneuver nodes** — easy to add (`Vessel.GetManeuverNode()` etc.)
+  but not needed for the live map / mission clock.
+
+## Troubleshooting
+
+### `no kRPC server at 127.0.0.1:50000`
+
+Either KSP isn't running, or the kRPC server isn't enabled. Open the
+kRPC window in-game (<kbd>Alt</kbd>+<kbd>F12</kbd>) and make sure
+"Start server" is checked.
+
+### `procedure not found in service cache`
+
+The kRPC server returned a procedure that we don't know about. This
+usually means the kRPC version is older or newer than we expect
+(we target 0.5.x). The ServiceCache will log the procedures it knows
+about; cross-check with the in-game kRPC window.
+
+### `wrong number of arguments`
+
+The procedure signature in the cache doesn't match what we're sending.
+This can happen if the kRPC version has a different parameter order
+or count for a procedure we use. The fix is in
+`apps/tools/ksp-bridge/src/extract.ts` — adjust the call site.

packages/krpc-client/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "@kerbal-rt/krpc-client",
+  "version": "0.1.0",
+  "private": true,
+  "description": "TypeScript client for the kRPC protobuf protocol (KSP telemetry bridge)",
+  "type": "module",
+  "main": "./src/index.ts",
+  "types": "./src/index.ts",
+  "exports": {
+    ".": "./src/index.ts"
+  },
+  "scripts": {
+    "typecheck": "tsc --noEmit",
+    "lint": "echo 'no linter yet'",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "build": "tsc"
+  },
+  "dependencies": {
+    "protobufjs": "^7.4.0"
+  },
+  "devDependencies": {
+    "@types/node": "^22.5.0",
+    "typescript": "^5.6.2",
+    "vitest": "^2.1.1"
+  }
+}

packages/krpc-client/src/_test-encode.ts

@@ -0,0 +1,51 @@
+/**
+ * Test-only encoding helpers for the value encoding tests.
+ *
+ * These are exact mirrors of the kRPC wire encoding for the primitive
+ * types we use in test fixtures. Imported by the integration test that
+ * drives a mock kRPC server.
+ *
+ * DO NOT use these in production code; use `encodeValue` from decoder.ts
+ * which dispatches based on the KrpcType descriptor.
+ */
+import { encodeVarint } from './connection.js';
+
+export function encodeDouble(v: number): Uint8Array {
+  const out = new Uint8Array(8);
+  new DataView(out.buffer).setFloat64(0, v, true);
+  return out;
+}
+
+export function encodeFloat(v: number): Uint8Array {
+  const out = new Uint8Array(4);
+  new DataView(out.buffer).setFloat32(0, v, true);
+  return out;
+}
+
+export function encodeSint32(v: number): Uint8Array {
+  return encodeVarint(((v << 1) ^ (v >> 31)) >>> 0);
+}
+
+export function encodeUint32(v: number): Uint8Array {
+  return encodeVarint(v);
+}
+
+export function encodeUint64(v: bigint): Uint8Array {
+  const out: number[] = [];
+  let x = v;
+  while (x >= 0x80n) {
+    out.push(Number((x & 0x7fn) | 0x80n));
+    x >>= 7n;
+  }
+  out.push(Number(x));
+  return new Uint8Array(out);
+}
+
+export function encodeString(v: string): Uint8Array {
+  const utf8 = new TextEncoder().encode(v);
+  return Buffer.concat([encodeVarint(utf8.length), Buffer.from(utf8)]);
+}
+
+export function encodeBool(v: boolean): Uint8Array {
+  return new Uint8Array([v ? 1 : 0]);
+}

packages/krpc-client/src/client.ts

@@ -0,0 +1,376 @@
+/**
+ * High-level kRPC client. Wraps the low-level connection/protocol
+ * to provide typed procedure calls and stream subscriptions.
+ *
+ * Lifecycle:
+ *   const client = new KRPCClient({ host, rpcPort, streamPort });
+ *   await client.connect();           // handshake on both ports
+ *   const ut = await client.invoke({ service: 'SpaceCenter',
+ *                                     procedure: 'GetUT' });
+ *   const streamId = await client.addStream({ service: 'SpaceCenter',
+ *                                             procedure: 'GetUT' });
+ *   client.onStreamUpdate((upd) => { ... });
+ *   await client.close();
+ */
+import * as net from 'node:net';
+import { Buffer } from 'node:buffer';
+import { KRPC, decodeMessage } from './schema.js';
+import { sendMessage, recvRawMessage, tcpConnect } from './connection.js';
+
+export interface KRPCClientOptions {
+  host?: string;
+  rpcPort?: number;
+  streamPort?: number;
+  clientName?: string;
+  connectTimeoutMs?: number;
+}
+
+export interface ProcedureCallRequest {
+  service: string;
+  procedure: string;
+  /** Optional argument values; position inferred from array order. */
+  args?: unknown[];
+  /** When set, used as service_id/procedure_id (saves a string lookup). */
+  serviceId?: number;
+  procedureId?: number;
+}
+
+type StreamHandler = (streamId: number, result: Uint8Array) => void;
+export type { StreamHandler };
+
+/**
+ * Format an error value for human consumption. Handles the cases where
+ * the thrown value is null, undefined, a string, or an Error with
+ * .code (NodeJS.ErrnoException). Falls back to JSON.stringify for
+ * unknown shapes.
+ */
+function formatErr(e: unknown): string {
+  if (e === null) return 'null';
+  if (e === undefined) return 'undefined';
+  if (typeof e === 'string') return e;
+  if (typeof e === 'object') {
+    const obj = e as { code?: unknown; message?: unknown; errno?: unknown };
+    const parts: string[] = [];
+    if (typeof obj.code === 'string') parts.push(`code=${obj.code}`);
+    if (typeof obj.errno === 'number') parts.push(`errno=${obj.errno}`);
+    if (typeof obj.message === 'string') parts.push(obj.message);
+    if (parts.length > 0) return parts.join(': ');
+    try {
+      return JSON.stringify(e);
+    } catch {
+      return String(e);
+    }
+  }
+  return String(e);
+}
+
+export class KRPCClient {
+  private opts: Required<KRPCClientOptions>;
+  private rpcSocket: net.Socket | null = null;
+  private streamSocket: net.Socket | null = null;
+  private clientIdentifier: Buffer = Buffer.alloc(0);
+  private streamHandlers = new Set<StreamHandler>();
+  private streamReadChain: Promise<void> = Promise.resolve();
+  private closed = false;
+
+  constructor(opts: KRPCClientOptions = {}) {
+    this.opts = {
+      host: opts.host ?? '127.0.0.1',
+      rpcPort: opts.rpcPort ?? 50000,
+      streamPort: opts.streamPort ?? 50001,
+      clientName: opts.clientName ?? 'kerbal-rt-bridge',
+      connectTimeoutMs: opts.connectTimeoutMs ?? 5000,
+    };
+  }
+
+  async connect(): Promise<void> {
+    // Wrap EVERYTHING in a top-level try so we always get a clean
+    // error message (not a buried TypeError from protobufjs
+    // nested-enum resolution). The specific sub-step failures are
+    // caught inline for nicer messages, but this top-level guard
+    // is the safety net.
+    try {
+      return await this._connectImpl();
+    } catch (e) {
+      throw new Error(`kRPC connect failed at unknown step: ${formatErr(e)} (stack: ${e instanceof Error ? e.stack : 'n/a'})`);
+    }
+  }
+
+  private async _connectImpl(): Promise<void> {
+    // RPC handshake
+    try {
+      this.rpcSocket = await tcpConnect(
+        this.opts.host,
+        this.opts.rpcPort,
+        this.opts.connectTimeoutMs,
+      );
+    } catch (e) {
+      throw new Error(
+        `kRPC RPC TCP connect to ${this.opts.host}:${this.opts.rpcPort} failed: ${formatErr(e)}`,
+      );
+    }
+    // The ConnectionRequest.Type enum has RPC = 0, STREAM = 1. We pass
+    // the numeric value directly because the nested-enum name lookup
+    // is brittle across protobufjs versions when the enum is nested
+    // inside the message.
+    sendMessage(this.rpcSocket, KRPC.ConnectionRequest, {
+      type: 0, // RPC
+      clientName: this.opts.clientName,
+    });
+    let resp: { status: number | string; message: string; clientIdentifier: Uint8Array };
+    try {
+      const rpcRaw = await recvRawMessage(this.rpcSocket);
+      if (process.env.KRPC_DEBUG) {
+        // eslint-disable-next-line no-console
+        console.log(
+          '[krpc-client] rpc handshake raw response (' + rpcRaw.length + ' bytes):',
+          Buffer.from(rpcRaw).toString('hex'),
+        );
+      }
+      resp = decodeMessage<{
+        status: number | string;
+        message: string;
+        clientIdentifier: Uint8Array;
+      }>(KRPC.ConnectionResponse, rpcRaw);
+    } catch (e) {
+      throw new Error(`kRPC RPC handshake (response decode) failed: ${formatErr(e)}`);
+    }
+    // protobufjs decodes enums to numbers by default; OK == 0
+    if (resp.status !== 'OK' && resp.status !== 0) {
+      throw new Error(`RPC handshake failed: ${resp.status} ${resp.message}`);
+    }
+    this.clientIdentifier = Buffer.from(resp.clientIdentifier);
+
+    // Stream handshake
+    try {
+      this.streamSocket = await tcpConnect(
+        this.opts.host,
+        this.opts.streamPort,
+        this.opts.connectTimeoutMs,
+      );
+    } catch (e) {
+      throw new Error(
+        `kRPC Stream TCP connect to ${this.opts.host}:${this.opts.streamPort} failed: ${formatErr(e)}`,
+      );
+    }
+    sendMessage(this.streamSocket, KRPC.ConnectionRequest, {
+      type: 1, // STREAM
+      clientIdentifier: this.clientIdentifier,
+    });
+    let streamResp: { status: number | string; message: string };
+    try {
+      const streamRaw = await recvRawMessage(this.streamSocket);
+      // Diagnostic: log the raw bytes for the stream handshake response
+      // so we can see what the kRPC server actually sent. Useful when
+      // debugging "Cannot read properties of null" type errors.
+      if (process.env.KRPC_DEBUG) {
+        // eslint-disable-next-line no-console
+        console.log(
+          '[krpc-client] stream handshake raw response (' + streamRaw.length + ' bytes):',
+          Buffer.from(streamRaw).toString('hex'),
+        );
+      }
+      streamResp = decodeMessage<{ status: number | string; message: string }>(
+        KRPC.ConnectionResponse,
+        streamRaw,
+      );
+    } catch (e) {
+      throw new Error(`kRPC Stream handshake (response decode) failed: ${formatErr(e)}`);
+    }
+    if (streamResp.status !== 'OK' && streamResp.status !== 0) {
+      throw new Error(`Stream handshake failed: ${streamResp.status} ${streamResp.message}`);
+    }
+
+    // Start the stream read loop
+    this.streamReadChain = this.readStreamLoop().catch((err) => {
+      // eslint-disable-next-line no-console
+      console.error('[krpc-client] stream loop error:', err);
+    });
+  } // end _connectImpl
+
+  isConnected(): boolean {
+    return this.rpcSocket !== null && this.streamSocket !== null && !this.closed;
+  }
+
+  /**
+   * Invoke a single procedure. Returns the raw return-value bytes.
+   * Use the .proto schema to decode it.
+   */
+  async invoke(req: ProcedureCallRequest): Promise<Uint8Array> {
+    if (!this.rpcSocket) throw new Error('not connected');
+    const call: Record<string, unknown> = {
+      service: req.service,
+      procedure: req.procedure,
+    };
+    if (req.serviceId !== undefined) call.serviceId = req.serviceId;
+    if (req.procedureId !== undefined) call.procedureId = req.procedureId;
+    if (req.args && req.args.length > 0) {
+      // Each argument must be a serialized protobuf value. For simple
+      // scalar types (double, float, string, bool, int), protobufjs
+      // can encode them with a wrapper type — but typically kRPC
+      // arguments are more complex (Class references, Tuples, etc.)
+      // and the caller must serialize them.
+      // For convenience, we accept already-encoded bytes here.
+      call.arguments = req.args.map((value, i) => {
+        if (value instanceof Uint8Array) {
+          return { position: i, value };
+        }
+        if (Buffer.isBuffer(value)) {
+          return { position: i, value };
+        }
+        // Last resort: try to encode as a string, since most basic
+        // kRPC args in our use case are simple types
+        return { position: i, value: Buffer.from(String(value)) };
+      });
+    }
+    sendMessage(this.rpcSocket, KRPC.Request, { calls: [call] });
+    const raw = await recvRawMessage(this.rpcSocket);
+    if (process.env.KRPC_DEBUG) {
+      // eslint-disable-next-line no-console
+      console.log(
+        `[krpc-client] ${req.service}.${req.procedure} response (${raw.length} bytes):`,
+        Buffer.from(raw).toString('hex'),
+      );
+    }
+    // The kRPC schema defines `error` as a sub-message of type Error
+    // (not raw bytes), so protobufjs decodes it as a nested object
+    // automatically — service/name/description/stackTrace are already
+    // populated when the field is set.
+    const response = decodeMessage<{
+      error?: { service: string; name: string; description: string; stackTrace: string };
+      results: {
+        error?: { service: string; name: string; description: string; stackTrace: string };
+        value: Uint8Array;
+      }[];
+    }>(KRPC.Response, raw);
+    if (response.error) {
+      throw new Error(
+        `RPC error: ${response.error.service}.${response.error.name}: ${response.error.description}` +
+          (response.error.stackTrace ? `\n${response.error.stackTrace}` : ''),
+      );
+    }
+    if (response.results.length === 0) {
+      throw new Error('empty response');
+    }
+    const r = response.results[0];
+    if (!r) {
+      throw new Error('empty response result');
+    }
+    if (r.error) {
+      throw new Error(
+        `RPC result error: ${r.error.service}.${r.error.name}: ${r.error.description}` +
+          (r.error.stackTrace ? `\n${r.error.stackTrace}` : ''),
+      );
+    }
+    return r.value;
+  }
+
+  /**
+   * Subscribe to a procedure. Returns the stream id; updates are
+   * delivered via the onStreamUpdate callback.
+   */
+  async addStream(req: ProcedureCallRequest): Promise<number> {
+    if (!this.rpcSocket) throw new Error('not connected');
+    // The argument to AddStream is a ProcedureCall describing the
+    // procedure to stream.
+    const innerCall: Record<string, unknown> = {
+      service: req.service,
+      procedure: req.procedure,
+    };
+    if (req.serviceId !== undefined) innerCall.serviceId = req.serviceId;
+    if (req.procedureId !== undefined) innerCall.procedureId = req.procedureId;
+    const innerCallBytes = Buffer.from(
+      KRPC.ProcedureCall.encode(KRPC.ProcedureCall.create(innerCall)).finish(),
+    );
+    const addCall = {
+      service: 'KRPC',
+      procedure: 'AddStream',
+      arguments: [{ position: 0, value: innerCallBytes }],
+    };
+    sendMessage(this.rpcSocket, KRPC.Request, { calls: [addCall] });
+    const response = decodeMessage<{
+      results: {
+        value: Uint8Array;
+        error?: { service: string; name: string; description: string; stackTrace: string };
+      }[];
+    }>(KRPC.Response, await recvRawMessage(this.rpcSocket));
+    if (response.results.length === 0) throw new Error('empty AddStream response');
+    const r0 = response.results[0];
+    if (!r0) throw new Error('empty AddStream result');
+    if (r0.error) {
+      throw new Error(
+        `AddStream error: ${r0.error.service}.${r0.error.name}: ${r0.error.description}`,
+      );
+    }
+    const stream = decodeMessage<{ id: number }>(KRPC.Stream, r0.value);
+    return stream.id;
+  }
+
+  /** Remove a previously added stream. */
+  async removeStream(streamId: number): Promise<void> {
+    if (!this.rpcSocket) throw new Error('not connected');
+    const streamMsg = KRPC.Stream.create({ id: streamId });
+    const streamBytes = Buffer.from(KRPC.Stream.encode(streamMsg).finish());
+    const call = {
+      service: 'KRPC',
+      procedure: 'RemoveStream',
+      arguments: [{ position: 0, value: streamBytes }],
+    };
+    sendMessage(this.rpcSocket, KRPC.Request, { calls: [call] });
+    await recvRawMessage(this.rpcSocket);
+  }
+
+  /** Register a callback invoked for every stream update. */
+  onStreamUpdate(handler: StreamHandler): () => void {
+    this.streamHandlers.add(handler);
+    return () => this.streamHandlers.delete(handler);
+  }
+
+  async close(): Promise<void> {
+    if (this.closed) return;
+    this.closed = true;
+    if (this.rpcSocket) {
+      this.rpcSocket.destroy();
+      this.rpcSocket = null;
+    }
+    if (this.streamSocket) {
+      this.streamSocket.destroy();
+      this.streamSocket = null;
+    }
+    await this.streamReadChain.catch(() => undefined);
+  }
+
+  // ── private ──────────────────────────────────────────────────────────
+
+  private async readStreamLoop(): Promise<void> {
+    if (!this.streamSocket) return;
+    while (!this.closed) {
+      try {
+        const raw = await recvRawMessage(this.streamSocket);
+        const update = decodeMessage<{
+          results: {
+            id: number;
+            result: {
+              error?: { service: string; name: string; description: string; stackTrace: string };
+              value: Uint8Array;
+            };
+          }[];
+        }>(KRPC.StreamUpdate, raw);
+        for (const r of update.results) {
+          if (r.result.error) {
+            // eslint-disable-next-line no-console
+            console.warn(
+              `[krpc-client] stream ${r.id} error: ${r.result.error.service}.${r.result.error.name}: ${r.result.error.description}`,
+            );
+            for (const h of this.streamHandlers) h(r.id, new Uint8Array());
+            continue;
+          }
+          for (const h of this.streamHandlers) h(r.id, r.result.value);
+        }
+      } catch (err) {
+        if (this.closed) return;
+        throw err;
+      }
+    }
+  }
+}

packages/krpc-client/src/connection.ts

@@ -0,0 +1,182 @@
+/**
+ * KRPC TCP connection — length-prefixed protobuf framing.
+ *
+ * Wire format (from krpc docs):
+ *  - Each message is encoded as: [varint length][protobuf payload]
+ *  - varint is the standard protobuf base-128 varint
+ *
+ * Uses a per-socket reader that buffers incoming data and fulfills
+ * pending read requests, avoiding race conditions when multiple
+ * read promises are in flight.
+ */
+import * as net from 'node:net';
+import { Buffer } from 'node:buffer';
+import protobuf from 'protobufjs';
+
+/** Encode an unsigned integer as a protobuf varint. */
+export function encodeVarint(value: number): Buffer {
+  if (value < 0) {
+    throw new Error('varint cannot encode negative numbers');
+  }
+  const bytes: number[] = [];
+  let v = value;
+  while (v >= 0x80) {
+    bytes.push((v & 0x7f) | 0x80);
+    v = Math.floor(v / 0x80);
+  }
+  bytes.push(v & 0x7f);
+  return Buffer.from(bytes);
+}
+
+/** Decode a protobuf varint from the front of a buffer. Returns [value, bytesConsumed]. */
+export function decodeVarint(buf: Buffer): [number, number] {
+  let result = 0;
+  let shift = 0;
+  let pos = 0;
+  while (pos < buf.length) {
+    const b = buf[pos++];
+    // Use multiplication by powers of 2 instead of `<<` because
+    // JavaScript's left-shift operator truncates to 32 bits, which
+    // would corrupt values ≥ 2^32 (e.g. uint64 stream ids).
+    result += (b & 0x7f) * Math.pow(2, shift);
+    if ((b & 0x80) === 0) {
+      return [result, pos];
+    }
+    shift += 7;
+    if (shift > 63) {
+      throw new Error('varint too long');
+    }
+  }
+  throw new Error('varint truncated');
+}
+
+/** Send a length-prefixed protobuf message. */
+export function sendMessage(
+  socket: net.Socket,
+  type: protobuf.Type,
+  value: Record<string, unknown>,
+): void {
+  const payload = Buffer.from(type.encode(type.create(value)).finish());
+  const prefix = encodeVarint(payload.length);
+  socket.write(Buffer.concat([prefix, payload]));
+}
+
+/**
+ * Per-socket reader. Buffers incoming chunks and resolves pending
+ * read requests. Prevents race conditions when multiple read promises
+ * are pending on the same socket.
+ */
+class SocketReader {
+  private buf: Buffer = Buffer.alloc(0);
+  private waiting: Array<{ n: number; resolve: (b: Buffer) => void; reject: (e: Error) => void }> =
+    [];
+  private closed = false;
+  private closeReason: Error | null = null;
+
+  constructor(socket: net.Socket) {
+    socket.on('data', (chunk: Buffer) => this.onData(chunk));
+    socket.on('error', (err) => this.onClose(err));
+    socket.on('close', () => this.onClose(new Error('socket closed')));
+  }
+
+  read(n: number): Promise<Buffer> {
+    if (this.closed) {
+      return Promise.reject(this.closeReason ?? new Error('socket closed'));
+    }
+    if (this.buf.length >= n) {
+      const out = this.buf.subarray(0, n);
+      this.buf = this.buf.subarray(n);
+      return Promise.resolve(Buffer.from(out));
+    }
+    return new Promise((resolve, reject) => {
+      this.waiting.push({ n, resolve, reject });
+    });
+  }
+
+  private onData(chunk: Buffer): void {
+    this.buf = Buffer.concat([this.buf, chunk]);
+    // Try to satisfy pending reads (in order)
+    let i = 0;
+    while (i < this.waiting.length) {
+      const w = this.waiting[i]!;
+      if (this.buf.length >= w.n) {
+        const out = this.buf.subarray(0, w.n);
+        this.buf = this.buf.subarray(w.n);
+        w.resolve(Buffer.from(out));
+        this.waiting.splice(i, 1);
+      } else {
+        i++;
+      }
+    }
+  }
+
+  private onClose(err: Error): void {
+    if (this.closed) return;
+    this.closed = true;
+    this.closeReason = err;
+    while (this.waiting.length > 0) {
+      const w = this.waiting.shift()!;
+      w.reject(err);
+    }
+  }
+}
+
+const readers = new WeakMap<net.Socket, SocketReader>();
+
+function readerFor(socket: net.Socket): SocketReader {
+  let r = readers.get(socket);
+  if (!r) {
+    r = new SocketReader(socket);
+    readers.set(socket, r);
+  }
+  return r;
+}
+
+/** Receive a single length-prefixed message and return the raw bytes. */
+export async function recvRawMessage(socket: net.Socket): Promise<Uint8Array> {
+  const reader = readerFor(socket);
+  // Read varint length one byte at a time
+  let lenBuf = Buffer.alloc(0);
+  while (true) {
+    const b = await reader.read(1);
+    lenBuf = Buffer.concat([lenBuf, b]);
+    try {
+      const [length, _consumed] = decodeVarint(lenBuf);
+      if (length > 16 * 1024 * 1024) {
+        throw new Error('message too large');
+      }
+      return await reader.read(length);
+    } catch (e) {
+      if ((e as Error).message === 'varint truncated') {
+        continue;
+      }
+      throw e;
+    }
+  }
+}
+
+/** Receive a single length-prefixed message and decode it. */
+export async function recvMessage<T>(socket: net.Socket, type: protobuf.Type): Promise<T> {
+  const payload = await recvRawMessage(socket);
+  return type.decode(payload) as T;
+}
+
+/** Open a TCP connection to a host:port. */
+export function tcpConnect(host: string, port: number, timeoutMs = 5000): Promise<net.Socket> {
+  return new Promise((resolve, reject) => {
+    const socket = net.createConnection({ host, port });
+    const timer = setTimeout(() => {
+      socket.destroy();
+      reject(new Error(`connect timeout after ${timeoutMs}ms`));
+    }, timeoutMs);
+    socket.once('connect', () => {
+      clearTimeout(timer);
+      socket.setNoDelay(true);
+      resolve(socket);
+    });
+    socket.once('error', (err) => {
+      clearTimeout(timer);
+      reject(err);
+    });
+  });
+}

packages/krpc-client/src/decoder.ts

@@ -0,0 +1,478 @@
+/**
+ * kRPC value decoder.
+ *
+ * kRPC values are encoded on the wire using a hybrid scheme:
+ *
+ *  - For **primitive types** (DOUBLE, FLOAT, SINT32, SINT64, UINT32, UINT64,
+ *    BOOL, STRING, BYTES) the bytes are exactly the standard protobuf wire
+ *    encoding of that single value, NOT wrapped in a message. So a `double`
+ *    is just 8 little-endian bytes, a `string` is `[varint length][utf8]`,
+ *    and so on.
+ *
+ *  - For **CLASS types** the bytes are a single varint-encoded `uint64` —
+ *    the object id. An object id of 0 means `None` (the CLASS is nullable).
+ *    The actual class data lives server-side; to get a property you call
+ *    `Service.ClassName.GetX(id)`.
+ *
+ *  - For **ENUMERATION** the bytes are a single signed varint (zigzag-encoded
+ *    sint32 in protobuf terms).
+ *
+ *  - For **collections** (LIST, SET, TUPLE, DICTIONARY) the bytes are a
+ *    serialized `KRPC.List` / `KRPC.Set` / `KRPC.Tuple` / `KRPC.Dictionary`
+ *    message. Each element is itself encoded using the scheme above (so the
+ *    element bytes are variable-length). A null collection is a single byte
+ *    `\x00` (NOT a length-prefixed empty list).
+ *
+ *  - For **system messages** (STATUS, SERVICES, STREAM, EVENT,
+ *    PROCEDURE_CALL) the bytes are the standard protobuf serialization of
+ *    the corresponding KRPC message.
+ *
+ * Reference: the Python client's `krpc/decoder.py` (Krpc 0.5.x).
+ */
+import protobuf from 'protobufjs';
+import { decodeVarint, encodeVarint } from './connection.js';
+import { TypeCode, type KrpcType, typeName } from './types.js';
+
+/** Result of decoding a value. */
+export type DecodedValue =
+  | number
+  | bigint
+  | boolean
+  | string
+  | Uint8Array
+  | null
+  | DecodedValue[]
+  | Set<DecodedValue>
+  | Map<DecodedValue, DecodedValue>
+  | { [k: string]: unknown };
+
+/**
+ * Decode a value from its wire bytes according to a KrpcType.
+ *
+ * @param type       The KrpcType descriptor (from GetServices or a
+ *                   pre-built cache).
+ * @param data       The raw bytes (response.value for returns, or
+ *                   the value field of a KRPC.Argument for args).
+ * @param messageTypes Optional protobufjs type registry for decoding
+ *                   system messages (KRPC.Status, etc.) by name.
+ *                   Only needed for MESSAGE-style TypeCodes.
+ */
+export function decodeValue(
+  type: KrpcType,
+  data: Uint8Array,
+  messageTypes?: Record<string, protobuf.Type>,
+): DecodedValue {
+  switch (type.code) {
+    case TypeCode.NONE:
+      return null;
+
+    case TypeCode.DOUBLE:
+      return decodeDouble(data);
+    case TypeCode.FLOAT:
+      return decodeFloat(data);
+    case TypeCode.SINT32:
+      return decodeSint32(data);
+    case TypeCode.SINT64:
+      return decodeSint64(data);
+    case TypeCode.UINT32:
+      return decodeUint32(data);
+    case TypeCode.UINT64:
+      return decodeUint64(data);
+    case TypeCode.BOOL:
+      return decodeBool(data);
+    case TypeCode.STRING:
+      return decodeString(data);
+    case TypeCode.BYTES:
+      return decodeBytes(data);
+
+    case TypeCode.CLASS: {
+      // The wire form of a CLASS is a uint64 object id; 0 = None.
+      // We decode as a BigInt so callers can pass the id back as an
+      // argument to other class methods.
+      const id = bigFromVarint(data);
+      return id === 0n ? null : id;
+    }
+
+    case TypeCode.ENUMERATION: {
+      // Wire form: a single signed varint (sint32 in protobuf terms).
+      return decodeSint32(data);
+    }
+
+    case TypeCode.STATUS: {
+      return decodeSystemMessage('Status', data, messageTypes);
+    }
+    case TypeCode.SERVICES: {
+      return decodeSystemMessage('Services', data, messageTypes);
+    }
+    case TypeCode.STREAM: {
+      return decodeSystemMessage('Stream', data, messageTypes);
+    }
+    case TypeCode.EVENT: {
+      return decodeSystemMessage('Event', data, messageTypes);
+    }
+    case TypeCode.PROCEDURE_CALL: {
+      return decodeSystemMessage('ProcedureCall', data, messageTypes);
+    }
+
+    case TypeCode.LIST:
+      return decodeList(type, data, messageTypes);
+    case TypeCode.SET:
+      return decodeSet(type, data, messageTypes);
+    case TypeCode.TUPLE:
+      return decodeTuple(type, data, messageTypes);
+    case TypeCode.DICTIONARY:
+      return decodeDictionary(type, data, messageTypes);
+
+    default:
+      throw new Error(`unknown TypeCode ${type.code} (${typeName(type)})`);
+  }
+}
+
+// ── primitive decoders ──────────────────────────────────────────────────────
+
+/**
+ * Read a fixed-width little-endian IEEE 754 number from a buffer.
+ *
+ * JavaScript's `DataView.getFloat64()` already does the right thing on
+ * little-endian platforms, which Node always is. We still go through
+ * `DataView` so the intent is explicit and the code is portable to
+ * big-endian platforms (if we ever run on one).
+ */
+function readFloatLE(buf: Uint8Array, offset: number, bytes: 4 | 8): number {
+  // Pad short reads with zero bytes. This shouldn't happen in practice,
+  // but it's defensive against a truncated response.
+  if (buf.length < offset + bytes) {
+    const padded = new Uint8Array(bytes);
+    padded.set(buf.subarray(offset, offset + bytes));
+    buf = padded;
+    offset = 0;
+  }
+  const view = new DataView(buf.buffer, buf.byteOffset + offset, bytes);
+  return bytes === 8 ? view.getFloat64(0, true) : view.getFloat32(0, true);
+}
+
+export function decodeDouble(data: Uint8Array): number {
+  return readFloatLE(data, 0, 8);
+}
+
+export function decodeFloat(data: Uint8Array): number {
+  return readFloatLE(data, 0, 4);
+}
+
+export function decodeSint32(data: Uint8Array): number {
+  // Protobuf sint32 is zigzag-encoded. `decodeVarint` returns a regular
+  // varint, so we need the zigzag step too.
+  const [raw] = decodeVarint(Buffer.from(data));
+  return zigzagDecode(Number(raw));
+}
+
+export function decodeSint64(data: Uint8Array): number {
+  // The Python client decodes sint64 to a plain int (BigInt in their
+  // case is a separate branch). For our use case the values we care
+  // about (enum cases) are well within int32 range, so we decode to
+  // a JS number. If you really need full int64, decode to BigInt.
+  return decodeSint32(data);
+}
+
+export function decodeUint32(data: Uint8Array): number {
+  const [v] = decodeVarint(Buffer.from(data));
+  return Number(v);
+}
+
+export function decodeUint64(data: Uint8Array): bigint {
+  // Use BigInt for the 64-bit case. The kRPC ObjectId and StreamId are
+  // uint64s and can exceed Number.MAX_SAFE_INTEGER in principle
+  // (though kRPC never generates ids that large in practice).
+  return bigFromVarint(data);
+}
+
+export function decodeBool(data: Uint8Array): boolean {
+  if (data.length < 1) return false;
+  return data[0] !== 0;
+}
+
+export function decodeString(data: Uint8Array): string {
+  // Wire form: [varint length][utf8 bytes].
+  const buf = Buffer.from(data);
+  const [len, pos] = decodeVarint(buf);
+  return buf.subarray(pos, pos + Number(len)).toString('utf-8');
+}
+
+export function decodeBytes(data: Uint8Array): Uint8Array {
+  const buf = Buffer.from(data);
+  const [len, pos] = decodeVarint(buf);
+  return new Uint8Array(buf.subarray(pos, pos + Number(len)));
+}
+
+function zigzagDecode(n: number): number {
+  return (n >>> 1) ^ -(n & 1);
+}
+
+/**
+ * Decode a varint (assumed ≤ 64 bits) as a BigInt. Used for uint64 values
+ * where the precision loss of Number() is unacceptable.
+ */
+function bigFromVarint(data: Uint8Array): bigint {
+  let result = 0n;
+  let shift = 0n;
+  for (let i = 0; i < data.length; i++) {
+    const b = data[i];
+    if (b === undefined) break;
+    result |= BigInt(b & 0x7f) << shift;
+    if ((b & 0x80) === 0) return result;
+    shift += 7n;
+  }
+  return result;
+}
+
+// ── collection decoders ─────────────────────────────────────────────────────
+
+/**
+ * Decode a KRPC.List message (when its serialized form is provided).
+ * Used internally by `decodeList`. Also exported for tests.
+ */
+export function decodeKrpcList(
+  data: Uint8Array,
+  messageType: protobuf.Type,
+): Uint8Array[] {
+  if (data.length === 1 && data[0] === 0) {
+    // A list may be serialized as a single 0x00 byte to indicate None.
+    return [];
+  }
+  const msg = messageType.decode(data) as unknown as { items: Uint8Array[] };
+  return msg.items ?? [];
+}
+
+export function decodeList(
+  type: KrpcType,
+  data: Uint8Array,
+  messageTypes?: Record<string, protobuf.Type>,
+): DecodedValue[] {
+  if (data.length === 1 && data[0] === 0) return null as unknown as DecodedValue[];
+  const listType = messageTypes?.['List'];
+  if (!listType) {
+    throw new Error('decodeList: no protobufjs type for KRPC.List registered');
+  }
+  const items = decodeKrpcList(data, listType);
+  const elemType = type.types[0];
+  if (!elemType) throw new Error('LIST type missing element type');
+  return items.map((it) => decodeValue(elemType, it, messageTypes));
+}
+
+export function decodeSet(
+  type: KrpcType,
+  data: Uint8Array,
+  messageTypes?: Record<string, protobuf.Type>,
+): Set<DecodedValue> {
+  if (data.length === 1 && data[0] === 0) return null as unknown as Set<DecodedValue>;
+  const setType = messageTypes?.['Set'];
+  if (!setType) {
+    throw new Error('decodeSet: no protobufjs type for KRPC.Set registered');
+  }
+  const msg = setType.decode(data) as unknown as { items: Uint8Array[] };
+  const elemType = type.types[0];
+  if (!elemType) throw new Error('SET type missing element type');
+  return new Set((msg.items ?? []).map((it) => decodeValue(elemType, it, messageTypes)));
+}
+
+export function decodeTuple(
+  type: KrpcType,
+  data: Uint8Array,
+  messageTypes?: Record<string, protobuf.Type>,
+): DecodedValue[] {
+  if (data.length === 1 && data[0] === 0) return null as unknown as DecodedValue[];
+  const tupleType = messageTypes?.['Tuple'];
+  if (!tupleType) {
+    throw new Error('decodeTuple: no protobufjs type for KRPC.Tuple registered');
+  }
+  const msg = tupleType.decode(data) as unknown as { items: Uint8Array[] };
+  return type.types.map((inner, i) =>
+    decodeValue(inner, msg.items[i] ?? new Uint8Array(0), messageTypes),
+  );
+}
+
+export function decodeDictionary(
+  type: KrpcType,
+  data: Uint8Array,
+  messageTypes?: Record<string, protobuf.Type>,
+): Map<DecodedValue, DecodedValue> {
+  if (data.length === 1 && data[0] === 0) {
+    return null as unknown as Map<DecodedValue, DecodedValue>;
+  }
+  const dictType = messageTypes?.['Dictionary'];
+  if (!dictType) {
+    throw new Error('decodeDictionary: no protobufjs type for KRPC.Dictionary registered');
+  }
+  const msg = dictType.decode(data) as unknown as {
+    entries: { key: Uint8Array; value: Uint8Array }[];
+  };
+  const keyType = type.types[0];
+  const valType = type.types[1];
+  if (!keyType || !valType) throw new Error('DICTIONARY type missing key/value types');
+  const out = new Map<DecodedValue, DecodedValue>();
+  for (const e of msg.entries ?? []) {
+    out.set(
+      decodeValue(keyType, e.key, messageTypes),
+      decodeValue(valType, e.value, messageTypes),
+    );
+  }
+  return out;
+}
+
+function decodeSystemMessage(
+  name: string,
+  data: Uint8Array,
+  messageTypes?: Record<string, protobuf.Type>,
+): { [k: string]: unknown } {
+  const t = messageTypes?.[name];
+  if (!t) throw new Error(`decodeSystemMessage: no type registered for ${name}`);
+  return t.decode(data) as unknown as { [k: string]: unknown };
+}
+
+// ── encoders (mirrors, for sending arguments) ───────────────────────────────
+
+/**
+ * Encode a value into the kRPC wire format for `type`.
+ *
+ * This is the inverse of `decodeValue`. Used by the service client to
+ * serialize procedure arguments. Collections and system messages use the
+ * protobufjs registry the same way the decoder does.
+ */
+export function encodeValue(
+  type: KrpcType,
+  value: DecodedValue,
+  messageTypes?: Record<string, protobuf.Type>,
+): Uint8Array {
+  switch (type.code) {
+    case TypeCode.NONE:
+      return new Uint8Array(0);
+    case TypeCode.DOUBLE:
+      return encodeDouble(value as number);
+    case TypeCode.FLOAT:
+      return encodeFloat(value as number);
+    case TypeCode.SINT32:
+      return encodeSint32(value as number);
+    case TypeCode.SINT64:
+      return encodeSint32(value as number);
+    case TypeCode.UINT32:
+      return encodeUint32(value as number);
+    case TypeCode.UINT64:
+      return encodeUint64(value as bigint);
+    case TypeCode.BOOL:
+      return encodeBool(value as boolean);
+    case TypeCode.STRING:
+      return encodeString(value as string);
+    case TypeCode.BYTES:
+      return encodeBytes(value as Uint8Array);
+
+    case TypeCode.CLASS: {
+      // CLASS args are encoded as uint64 object id; null = 0.
+      if (value === null || value === undefined) return encodeUint64(0n);
+      if (typeof value === 'bigint') return encodeUint64(value);
+      if (typeof value === 'number') return encodeUint64(BigInt(value));
+      throw new Error(`encodeValue: CLASS expects bigint object id, got ${typeof value}`);
+    }
+
+    case TypeCode.ENUMERATION:
+      return encodeSint32(value as number);
+
+    case TypeCode.LIST: {
+      const listType = messageTypes?.['List'];
+      if (!listType) throw new Error('encodeValue: no type for KRPC.List');
+      const elemType = type.types[0];
+      if (!elemType) throw new Error('LIST type missing element type');
+      const items = (value as DecodedValue[]).map((v) => encodeValue(elemType, v, messageTypes));
+      const msg = listType.create({ items });
+      return listType.encode(msg).finish();
+    }
+    case TypeCode.TUPLE: {
+      const tupleType = messageTypes?.['Tuple'];
+      if (!tupleType) throw new Error('encodeValue: no type for KRPC.Tuple');
+      const items = (value as DecodedValue[]).map((v, i) =>
+        encodeValue(type.types[i] as KrpcType, v, messageTypes),
+      );
+      const msg = tupleType.create({ items });
+      return tupleType.encode(msg).finish();
+    }
+    case TypeCode.DICTIONARY: {
+      const dictType = messageTypes?.['Dictionary'];
+      if (!dictType) throw new Error('encodeValue: no type for KRPC.Dictionary');
+      const keyType = type.types[0];
+      const valType = type.types[1];
+      if (!keyType || !valType) throw new Error('DICTIONARY type missing key/value types');
+      const entries: { key: Uint8Array; value: Uint8Array }[] = [];
+      for (const [k, v] of (value as Map<DecodedValue, DecodedValue>).entries()) {
+        entries.push({
+          key: encodeValue(keyType, k, messageTypes),
+          value: encodeValue(valType, v, messageTypes),
+        });
+      }
+      const msg = dictType.create({ entries });
+      return dictType.encode(msg).finish();
+    }
+    case TypeCode.SET: {
+      // kRPC 0.5 doesn't really use SET much; if needed we'd encode as
+      // KRPC.Set. For now, only LIST/TUPLE/DICT are exercised by our
+      // SpaceCenter calls.
+      throw new Error('encodeValue: SET not implemented (kRPC 0.5 does not use it)');
+    }
+    case TypeCode.STATUS:
+    case TypeCode.SERVICES:
+    case TypeCode.STREAM:
+    case TypeCode.EVENT:
+    case TypeCode.PROCEDURE_CALL:
+      throw new Error(`encodeValue: system message ${typeName(type)} cannot be sent as argument`);
+
+    default:
+      throw new Error(`encodeValue: unknown TypeCode ${type.code}`);
+  }
+}
+
+function encodeDouble(v: number): Uint8Array {
+  const out = new Uint8Array(8);
+  new DataView(out.buffer).setFloat64(0, v, true);
+  return out;
+}
+
+function encodeFloat(v: number): Uint8Array {
+  const out = new Uint8Array(4);
+  new DataView(out.buffer).setFloat32(0, v, true);
+  return out;
+}
+
+function encodeSint32(v: number): Uint8Array {
+  return encodeVarint(zigzagEncode(v));
+}
+
+function encodeUint32(v: number): Uint8Array {
+  return encodeVarint(v);
+}
+
+function encodeUint64(v: bigint): Uint8Array {
+  // Manual varint encoding for BigInt to avoid Number truncation.
+  const out: number[] = [];
+  let x = v;
+  while (x >= 0x80n) {
+    out.push(Number((x & 0x7fn) | 0x80n));
+    x >>= 7n;
+  }
+  out.push(Number(x));
+  return new Uint8Array(out);
+}
+
+function encodeBool(v: boolean): Uint8Array {
+  return new Uint8Array([v ? 1 : 0]);
+}
+
+function encodeString(v: string): Uint8Array {
+  const utf8 = new TextEncoder().encode(v);
+  return Buffer.concat([encodeVarint(utf8.length), Buffer.from(utf8)]);
+}
+
+function encodeBytes(v: Uint8Array): Uint8Array {
+  return Buffer.concat([encodeVarint(v.length), Buffer.from(v)]);
+}
+
+function zigzagEncode(n: number): number {
+  return (n << 1) ^ (n >> 31);
+}

packages/krpc-client/src/index.ts

@@ -0,0 +1,58 @@
+/**
+ * @kerbal-rt/krpc-client — TypeScript client for the kRPC protobuf
+ * protocol used by the Kerbal Space Program kRPC mod.
+ *
+ * Provides:
+ *  - KRPCClient: high-level wrapper with connect/invoke/addStream/close
+ *  - sendMessage / recvMessage / recvRawMessage / encodeVarint / decodeVarint:
+ *    low-level wire-format helpers
+ *  - KRPC namespace: protobufjs types for the kRPC meta-protocol
+ *  - KrpcType / TypeCode: runtime representation of kRPC type descriptors
+ *  - decodeValue / encodeValue: kRPC value codec (primitives, classes,
+ *    enums, collections, system messages)
+ *  - ServiceCache: a Type index built from KRPC.GetServices()
+ *  - KrpcServices: high-level invoke-by-name client
+ *
+ * For the service-specific types (SpaceCenter.Vessel, Orbit, etc.) we do
+ * NOT need to load the kRPC mod's .proto files. The server's
+ * GetServices() response contains everything we need to encode/decode
+ * values. See ./service-client.ts for the details.
+ */
+export {
+  KRPCClient,
+  type ProcedureCallRequest,
+  type KRPCClientOptions,
+  type StreamHandler,
+} from './client.js';
+export {
+  sendMessage,
+  recvMessage,
+  recvRawMessage,
+  encodeVarint,
+  decodeVarint,
+  tcpConnect,
+} from './connection.js';
+export { KRPC, encodeMessage, decodeMessage, MESSAGE_TYPES } from './schema.js';
+export {
+  TypeCode,
+  decodeKrpcType,
+  typeName,
+  type KrpcType,
+  type TypeCodeValue,
+  type RawKrpcTypeMessage,
+} from './types.js';
+export {
+  decodeValue,
+  encodeValue,
+  decodeDouble,
+  decodeFloat,
+  decodeSint32,
+  decodeUint32,
+  decodeUint64,
+  decodeBool,
+  decodeString,
+  decodeBytes,
+  type DecodedValue,
+} from './decoder.js';
+export { ServiceCache } from './services.js';
+export { KrpcServices, loadServices, type KrpcInvokeError } from './service-client.js';

packages/krpc-client/src/schema.ts

@@ -0,0 +1,383 @@
+/**
+ * kRPC meta-protocol schema (krpc.proto).
+ *
+ * This file contains the protobufjs JSON representation of the kRPC
+ * meta-protocol messages used to:
+ *  - Connect (ConnectionRequest, ConnectionResponse)
+ *  - Call procedures (Request, ProcedureCall, Argument, Response,
+ *    ProcedureResult, Error)
+ *  - Stream (StreamUpdate, StreamResult, Stream, Status, etc.)
+ *
+ * For SpaceCenter.Vessel/Orbit/CelestialBody types, see ./spacecenter.ts
+ * — those are loaded dynamically from the kRPC mod's .proto files
+ * when running against a real KSP instance.
+ */
+import protobuf from 'protobufjs';
+
+// We hand-write the JSON descriptor here so the package has no runtime
+// dependency on the .proto files (which ship inside the kRPC mod).
+// This is the minimum subset we need for the bridge to function.
+const schemaJson = {
+  nested: {
+    krpc: {
+      nested: {
+        schema: {
+          nested: {
+            ConnectionRequest: {
+              fields: {
+                type: { type: 'ConnectionRequest.Type', id: 1 },
+                clientName: { type: 'string', id: 2 },
+                clientIdentifier: { type: 'bytes', id: 3 },
+              },
+              nested: {
+                Type: {
+                  values: { RPC: 0, STREAM: 1 },
+                },
+              },
+            },
+            ConnectionResponse: {
+              // NOTE: status is wire-varint-enum-OK=0, but we model it
+              // as a plain uint32 to avoid protobufjs nested-enum
+              // resolution bugs that throw "Cannot read properties of
+              // null (reading 'code')" when the field is omitted from
+              // the wire (which the kRPC server does for the happy
+              // path). Our code already does `resp.status !== 0` /
+              // `!== 'OK'` checks that work for both numbers and the
+              // string 'OK' (the latter never happens after this fix).
+              fields: {
+                status: { type: 'uint32', id: 1 },
+                message: { type: 'string', id: 2 },
+                clientIdentifier: { type: 'bytes', id: 3 },
+              },
+              nested: {
+                Status: {
+                  values: {
+                    OK: 0,
+                    MALFORMED_MESSAGE: 1,
+                    TIMEOUT: 2,
+                    WRONG_TYPE: 3,
+                  },
+                },
+              },
+            },
+            Request: {
+              fields: {
+                calls: { rule: 'repeated', type: 'ProcedureCall', id: 1 },
+              },
+            },
+            Response: {
+              fields: {
+                error: { type: 'Error', id: 1 },
+                results: { rule: 'repeated', type: 'ProcedureResult', id: 2 },
+              },
+            },
+            ProcedureCall: {
+              fields: {
+                service: { type: 'string', id: 1 },
+                procedure: { type: 'string', id: 2 },
+                arguments: { rule: 'repeated', type: 'Argument', id: 3 },
+                serviceId: { type: 'uint32', id: 4 },
+                procedureId: { type: 'uint32', id: 5 },
+              },
+            },
+            Argument: {
+              fields: {
+                position: { type: 'uint32', id: 1 },
+                value: { type: 'bytes', id: 2 },
+              },
+            },
+            ProcedureResult: {
+              fields: {
+                // Same nested-enum-as-field-type issue as
+                // ConnectionResponse.status: when the server omits the
+                // error field (the happy path), protobufjs's enum
+                // resolution throws the same null.code TypeError. The
+                // actual kRPC wire format is just a normal message
+                // reference (or absent), so we use 'Message' (which
+                // protobufjs treats as an embedded message) instead
+                // of the nested-enum reference.
+                error: { type: 'Error', id: 1 },
+                value: { type: 'bytes', id: 2 },
+              },
+            },
+            Error: {
+              fields: {
+                service: { type: 'string', id: 1 },
+                name: { type: 'string', id: 2 },
+                description: { type: 'string', id: 3 },
+                stackTrace: { type: 'string', id: 4 },
+              },
+            },
+            StreamUpdate: {
+              fields: {
+                results: { rule: 'repeated', type: 'StreamResult', id: 1 },
+              },
+            },
+            StreamResult: {
+              fields: {
+                id: { type: 'uint64', id: 1 },
+                result: { type: 'ProcedureResult', id: 2 },
+              },
+            },
+            Stream: {
+              fields: { id: { type: 'uint64', id: 1 } },
+            },
+            Status: {
+              fields: {
+                version: { type: 'string', id: 1 },
+                bytesRead: { type: 'uint64', id: 2 },
+                bytesWritten: { type: 'uint64', id: 3 },
+                bytesReadRate: { type: 'float', id: 4 },
+                bytesWrittenRate: { type: 'float', id: 5 },
+                rpcsExecuted: { type: 'uint64', id: 6 },
+                rpcRate: { type: 'float', id: 7 },
+                oneRpcPerUpdate: { type: 'bool', id: 8 },
+                maxTimePerUpdate: { type: 'uint32', id: 9 },
+                adaptiveRateControl: { type: 'bool', id: 10 },
+                blockingRecv: { type: 'bool', id: 11 },
+                recvTimeout: { type: 'uint32', id: 12 },
+                timePerRpcUpdate: { type: 'float', id: 13 },
+                pollTimePerRpcUpdate: { type: 'float', id: 14 },
+                execTimePerRpcUpdate: { type: 'float', id: 15 },
+                streamRpcs: { type: 'uint32', id: 16 },
+                streamRpcsExecuted: { type: 'uint64', id: 17 },
+                streamRpcRate: { type: 'float', id: 18 },
+                timePerStreamUpdate: { type: 'float', id: 19 },
+              },
+            },
+            Services: {
+              fields: {
+                services: { rule: 'repeated', type: 'Service', id: 1 },
+              },
+            },
+            Service: {
+              fields: {
+                name: { type: 'string', id: 1 },
+                procedures: { rule: 'repeated', type: 'Procedure', id: 2 },
+                classes: { rule: 'repeated', type: 'Class', id: 3 },
+                enumerations: { rule: 'repeated', type: 'Enumeration', id: 4 },
+                exceptions: { rule: 'repeated', type: 'Exception', id: 5 },
+                documentation: { type: 'string', id: 6 },
+              },
+            },
+            Procedure: {
+              // The kRPC server sends `game_scenes` (a repeated
+              // GameScene enum, field 6) on every Procedure. The
+              // GameScene enum is nested inside Procedure. We model
+              // it as a repeated uint32 to dodge the protobufjs
+              // nested-enum default-value bug, same as Type.code and
+              // ConnectionResponse.status. We don't actually use this
+              // field on the client side; it's just here so the
+              // decoder doesn't choke on the wire bytes.
+              fields: {
+                name: { type: 'string', id: 1 },
+                parameters: { rule: 'repeated', type: 'Parameter', id: 2 },
+                returnType: { type: 'Type', id: 3 },
+                returnIsNullable: { type: 'bool', id: 4 },
+                documentation: { type: 'string', id: 5 },
+                gameScenes: { rule: 'repeated', type: 'uint32', id: 6 },
+              },
+              nested: {
+                GameScene: {
+                  values: {
+                    SPACE_CENTER: 0,
+                    FLIGHT: 1,
+                    TRACKING_STATION: 2,
+                    EDITOR_VAB: 3,
+                    EDITOR_SPH: 4,
+                    MISSION_BUILDER: 5,
+                  },
+                },
+              },
+            },
+            Parameter: {
+              fields: {
+                name: { type: 'string', id: 1 },
+                type: { type: 'Type', id: 2 },
+                defaultValue: { type: 'bytes', id: 3 },
+                nullable: { type: 'bool', id: 4 },
+              },
+            },
+            Class: {
+              fields: {
+                name: { type: 'string', id: 1 },
+                documentation: { type: 'string', id: 2 },
+              },
+            },
+            Enumeration: {
+              fields: {
+                name: { type: 'string', id: 1 },
+                values: { rule: 'repeated', type: 'EnumerationValue', id: 2 },
+                documentation: { type: 'string', id: 3 },
+              },
+            },
+            EnumerationValue: {
+              fields: {
+                name: { type: 'string', id: 1 },
+                value: { type: 'int32', id: 2 },
+                documentation: { type: 'string', id: 3 },
+              },
+            },
+            Exception: {
+              fields: {
+                name: { type: 'string', id: 1 },
+                documentation: { type: 'string', id: 2 },
+              },
+            },
+            Type: {
+              // The `code` field on Type is a wire-varint enum
+              // (TypeCode = uint32 under the hood). We model it as a
+              // plain uint32 to dodge the protobufjs nested-enum
+              // default-value lookup bug that throws
+              // "Cannot read properties of null (reading 'code')"
+              // when decoding a Type message whose code field is
+              // present. Same fix as ConnectionResponse.status.
+              // The values stay as a nested TypeCode enum for
+              // documentation / programmatic lookup (in services.ts).
+              fields: {
+                code: { type: 'uint32', id: 1 },
+                service: { type: 'string', id: 2 },
+                name: { type: 'string', id: 3 },
+                types: { rule: 'repeated', type: 'Type', id: 4 },
+              },
+              nested: {
+                TypeCode: {
+                  values: {
+                    NONE: 0,
+                    DOUBLE: 1,
+                    FLOAT: 2,
+                    SINT32: 3,
+                    SINT64: 4,
+                    UINT32: 5,
+                    UINT64: 6,
+                    BOOL: 7,
+                    STRING: 8,
+                    BYTES: 9,
+                    CLASS: 100,
+                    ENUMERATION: 101,
+                    EVENT: 200,
+                    PROCEDURE_CALL: 201,
+                    STREAM: 202,
+                    STATUS: 203,
+                    SERVICES: 204,
+                    TUPLE: 300,
+                    LIST: 301,
+                    SET: 302,
+                    DICTIONARY: 303,
+                  },
+                },
+              },
+            },
+            Tuple: {
+              fields: { items: { rule: 'repeated', type: 'bytes', id: 1 } },
+            },
+            List: {
+              fields: { items: { rule: 'repeated', type: 'bytes', id: 1 } },
+            },
+            Set: {
+              fields: { items: { rule: 'repeated', type: 'bytes', id: 1 } },
+            },
+            Dictionary: {
+              fields: {
+                entries: { rule: 'repeated', type: 'DictionaryEntry', id: 1 },
+              },
+            },
+            DictionaryEntry: {
+              fields: {
+                key: { type: 'bytes', id: 1 },
+                value: { type: 'bytes', id: 2 },
+              },
+            },
+            Event: {
+              fields: { stream: { type: 'Stream', id: 1 } },
+            },
+            Expression: {
+              fields: {
+                typ: { type: 'Type', id: 1 },
+                code: { type: 'string', id: 2 },
+              },
+            },
+          },
+        },
+      },
+    },
+  },
+};
+
+const root = protobuf.Root.fromJSON(schemaJson as protobuf.INamespace);
+const ns = root.lookup('krpc.schema') as protobuf.Namespace;
+const lookupType = (name: string): protobuf.Type =>
+  ns.lookupType(name) as protobuf.Type;
+
+/**
+ * All kRPC meta-protocol types, by their protobufjs Type objects.
+ *
+ * These are used by the decoder/encoder for system messages (Status,
+ * Services, Stream, Event, ProcedureCall) and collection types
+ * (List, Set, Tuple, Dictionary).
+ *
+ * The same Type objects are also exposed as `MESSAGE_TYPES` so the
+ * service client can register them with the decoder in one call.
+ *
+ * GOTCHA: protobufjs's nested-enum string-to-number lookup is brittle
+ * when the enum shares its name with a built-in JavaScript type or
+ * with a parent property. In particular, sending
+ *   encodeMessage(ConnectionRequest, { type: 'STREAM' })
+ * silently encodes as 0 (RPC) instead of 1. To avoid this, encode
+ * enum values by their numeric code rather than the string name.
+ */
+export const KRPC = {
+  ConnectionRequest: lookupType('ConnectionRequest'),
+  ConnectionResponse: lookupType('ConnectionResponse'),
+  Request: lookupType('Request'),
+  Response: lookupType('Response'),
+  ProcedureCall: lookupType('ProcedureCall'),
+  Argument: lookupType('Argument'),
+  ProcedureResult: lookupType('ProcedureResult'),
+  Error: lookupType('Error'),
+  StreamUpdate: lookupType('StreamUpdate'),
+  StreamResult: lookupType('StreamResult'),
+  Stream: lookupType('Stream'),
+  Status: lookupType('Status'),
+  Services: lookupType('Services'),
+  Service: lookupType('Service'),
+  Type: lookupType('Type'),
+  List: lookupType('List'),
+  Set: lookupType('Set'),
+  Tuple: lookupType('Tuple'),
+  Dictionary: lookupType('Dictionary'),
+  DictionaryEntry: lookupType('DictionaryEntry'),
+  Event: lookupType('Event'),
+  Expression: lookupType('Expression'),
+} as const;
+
+/**
+ * A name → protobufjs Type registry for system messages and collection
+ * types. The decoder/encoder accepts this as the `messageTypes` argument
+ * so it knows how to (de)serialize these specific messages.
+ */
+export const MESSAGE_TYPES: Record<string, protobuf.Type> = {
+  List: KRPC.List,
+  Set: KRPC.Set,
+  Tuple: KRPC.Tuple,
+  Dictionary: KRPC.Dictionary,
+  Status: KRPC.Status,
+  Services: KRPC.Services,
+  Stream: KRPC.Stream,
+  Event: KRPC.Event,
+  ProcedureCall: KRPC.ProcedureCall,
+};
+
+// Silence "type not used" — we keep the root reference for diagnostics
+// and to allow callers to load additional .proto files later if needed.
+void root;
+
+/** Encode a length-prefixed protobuf message. */
+export function encodeMessage(type: protobuf.Type, value: Record<string, unknown>): Buffer {
+  return Buffer.from(type.encode(type.create(value)).finish());
+}
+
+/** Decode a length-prefixed protobuf message. */
+export function decodeMessage<T>(type: protobuf.Type, buf: Uint8Array): T {
+  return type.decode(buf) as T;
+}

packages/krpc-client/src/service-client.ts

@@ -0,0 +1,196 @@
+/**
+ * KrpcServices — high-level service client.
+ *
+ * Wraps KRPCClient + ServiceCache to provide a clean invoke-by-name API:
+ *
+ *   const sc = new KrpcServices(client, cache);
+ *   const ut = await sc.invoke<number>('SpaceCenter', 'GetUT');
+ *   const bodyIds = await sc.invoke<bigint[]>('SpaceCenter', 'GetBodies');
+ *   const name = await sc.invoke<string>('SpaceCenter', 'CelestialBody.GetName', bodyId);
+ *
+ * The client looks up the procedure in the cache, encodes each argument
+ * using the procedure's parameter types, calls the procedure via the
+ * low-level client, then decodes the response using the return type.
+ *
+ * For class-returning procedures, the response is decoded as the object
+ * id (a BigInt), or `null` if the server returned id=0. The caller can
+ * then pass that BigInt to other class methods.
+ *
+ * This design means we don't need the kRPC mod's .proto files at all —
+ * the kRPC server provides the type information via GetServices(), and
+ * the kRPC value encoding is what our decoder handles.
+ */
+import type { KRPCClient, ProcedureCallRequest } from './client.js';
+import { decodeValue, encodeValue, type DecodedValue } from './decoder.js';
+import { MESSAGE_TYPES, KRPC, decodeMessage } from './schema.js';
+import type { KrpcType } from './types.js';
+import { ServiceCache, type RawServicesMessage } from './services.js';
+
+export interface KrpcInvokeError extends Error {
+  service: string;
+  name: string;
+  description: string;
+  stackTrace?: string;
+}
+
+/** Build a KrpcInvokeError with extra metadata attached. */
+function makeInvokeError(
+  service: string,
+  name: string,
+  description: string,
+  stackTrace?: string,
+): KrpcInvokeError {
+  const e = new Error(`${service}.${name}: ${description}`) as KrpcInvokeError;
+  e.service = service;
+  e.name = name;
+  e.description = description;
+  if (stackTrace) e.stackTrace = stackTrace;
+  return e;
+}
+
+export class KrpcServices {
+  constructor(
+    private readonly client: KRPCClient,
+    private readonly cache: ServiceCache,
+  ) {}
+
+  /**
+   * Invoke a procedure and return the decoded value.
+   *
+   * @param service e.g. "SpaceCenter"
+   * @param procedure e.g. "GetUT" or "CelestialBody.GetName" for class methods
+   * @param args The procedure arguments. Each is encoded according to the
+   *             procedure's parameter types (looked up from the cache).
+   *             Object ids for CLASS parameters are BigInts.
+   */
+  async invoke<T extends DecodedValue = DecodedValue>(
+    service: string,
+    procedure: string,
+    ...args: DecodedValue[]
+  ): Promise<T> {
+    const lookup = this.cache.lookup(service, procedure);
+    if (!lookup.found) {
+      throw makeInvokeError(
+        service,
+        procedure,
+        `procedure not found in service cache (known services: ${this.cache.serviceNames().join(', ')})`,
+      );
+    }
+    const info = lookup.info;
+    if (args.length !== info.parameters.length) {
+      throw makeInvokeError(
+        service,
+        procedure,
+        `wrong number of arguments: expected ${info.parameters.length}, got ${args.length}`,
+      );
+    }
+    const encodedArgs = info.parameters.map((p, i) => {
+      const v = args[i];
+      // For nullable CLASS parameters, accept `null`/`undefined` and encode as id=0.
+      if (p.nullable && (v === null || v === undefined)) {
+        return new Uint8Array(0);
+      }
+      return encodeValue(p.type, v, MESSAGE_TYPES);
+    });
+    // Low-level invoke needs Uint8Array values for each argument.
+    const req: ProcedureCallRequest = {
+      service: info.service,
+      procedure: info.name,
+      args: encodedArgs,
+    };
+    let rawValue: Uint8Array;
+    try {
+      rawValue = await this.client.invoke(req);
+    } catch (err) {
+      // The low-level client throws with a generic message; we wrap it
+      // with the service.procedure prefix so the caller knows which call
+      // failed. The original error is on the `cause` chain in newer
+      // Node, but to keep things simple we re-throw a tagged error.
+      const e = err as Error;
+      throw makeInvokeError(service, procedure, e.message, e.stack);
+    }
+    if (rawValue.length === 0) {
+      // Zero-length response. Only valid for:
+      //   - procedures with no return value (KrpcType NONE)
+      //   - nullable CLASS with id=0 — but that is 1 byte (0x00), not 0
+      // So we return null if the return type is NONE or nullable,
+      // otherwise throw.
+      if (info.returnType.code === 0 /* NONE */) {
+        return null as unknown as T;
+      }
+      if (info.returnIsNullable) {
+        return null as unknown as T;
+      }
+      throw makeInvokeError(
+        service,
+        procedure,
+        'zero-length response for non-nullable, non-NONE return type',
+      );
+    }
+    const decoded = decodeValue(info.returnType, rawValue, MESSAGE_TYPES);
+    if (decoded === null && !info.returnIsNullable) {
+      // Some primitives (e.g. uint64 = 0) might decode to falsy values
+      // that we don't want to confuse with null. But for CLASS/ENUM this
+      // is a real "no value" — and only valid for nullable returns.
+      throw makeInvokeError(
+        service,
+        procedure,
+        'decoded null for non-nullable return type',
+      );
+    }
+    return decoded as T;
+  }
+
+  /**
+   * Read a class property by calling its getter procedure. Equivalent to
+   *   invoke(service, "ClassName.GetPropName", objectId)
+   * but reads more naturally at the call site.
+   */
+  async getClassProperty<T extends DecodedValue = DecodedValue>(
+    service: string,
+    className: string,
+    propertyName: string,
+    objectId: bigint | null,
+  ): Promise<T> {
+    return this.invoke<T>(service, `${className}.${propertyName}`, objectId as DecodedValue);
+  }
+
+  /**
+   * Underlying service cache, exposed for callers that want to do
+   * procedural introspection (e.g. debug tools that list available
+   * services or resolve enum values).
+   */
+  getCache(): ServiceCache {
+    return this.cache;
+  }
+}
+
+/**
+ * Build a ServiceCache from a fresh KRPCClient. Convenience for the
+ * common "connect, get services, return ready client" pattern.
+ *
+ * The return value of `KRPC.GetServices()` is a serialized
+ * `KRPC.Services` message. We decode it using our protobufjs type
+ * definition, then convert the result to a `ServiceCache`.
+ */
+export async function loadServices(client: KRPCClient): Promise<{
+  cache: ServiceCache;
+  services: KrpcServices;
+}> {
+  const rawValue = await client.invoke({
+    service: 'KRPC',
+    procedure: 'GetServices',
+  });
+  // KRPC.Services is a system message — decode it using the
+  // registered protobufjs type.
+  const decoded = decodeMessage<RawServicesMessage>(KRPC.Services, rawValue);
+  // protobufjs decodes `services` field as a repeated Service; each
+  // Service has nested messages for Class, Enumeration, etc. that
+  // protobufjs also decodes. The shape matches our RawServicesMessage
+  // contract — but TypeScript doesn't know that, so we cast.
+  const cache = new ServiceCache(decoded);
+  return { cache, services: new KrpcServices(client, cache) };
+}
+
+/** Re-export for consumers that want to import KrpcType. */
+export type { KrpcType };

packages/krpc-client/src/services.ts

@@ -0,0 +1,248 @@
+/**
+ * ServiceCache — a queryable index over a KRPC.GetServices() response.
+ *
+ * After connecting to kRPC, the canonical first call is `KRPC.GetServices()`,
+ * which returns a `KRPC.Services` message describing every service, every
+ * class, every enum, and every procedure. We decode that into a lookup
+ * table keyed by (service, procedure) so the service client can ask:
+ *
+ *   - "what is the return type of SpaceCenter.GetBodies?"
+ *   - "what are the param types of SpaceCenter.CelestialBody.GetName?"
+ *   - "is SpaceCenter.VesselType.Ship == 0?"
+ *
+ * The cache is built once after connect, then read-only. It is decoupled
+ * from the network so it can be unit-tested by feeding in a hand-crafted
+ * Services message.
+ */
+import {
+  decodeKrpcType,
+  type KrpcType,
+  type RawKrpcTypeMessage,
+} from './types.js';
+
+/** Shape of the KRPC.GetServices() response after protobufjs decoding. */
+export interface RawServicesMessage {
+  services: RawServiceMessage[];
+}
+
+export interface RawServiceMessage {
+  name: string;
+  procedures: RawProcedureMessage[];
+  classes: { name: string }[];
+  enumerations: RawEnumerationMessage[];
+}
+
+export interface RawProcedureMessage {
+  name: string;
+  parameters: RawParameterMessage[];
+  returnType: RawKrpcTypeMessage;
+  returnIsNullable: boolean;
+}
+
+export interface RawParameterMessage {
+  name: string;
+  type: RawKrpcTypeMessage;
+  nullable: boolean;
+}
+
+export interface RawEnumerationMessage {
+  name: string;
+  values: { name: string; value: number }[];
+}
+
+export interface ProcedureInfo {
+  service: string;
+  name: string;
+  /** Full procedure name with class prefix, e.g. `CelestialBody.GetName`. */
+  fullName: string;
+  returnType: KrpcType;
+  returnIsNullable: boolean;
+  parameters: { name: string; type: KrpcType; nullable: boolean }[];
+}
+
+/**
+ * Result of a name lookup. Either we found the proc and we know its
+ * signature, or we didn't and the caller can decide what to do.
+ */
+export type ProcedureLookup =
+  | { found: true; info: ProcedureInfo }
+  | { found: false };
+
+/**
+ * Generate the .NET-style variants of a PascalCase procedure name.
+ * For a top-level procedure like "GetUT" -> ["get_UT"].
+ * For a class-prefixed one like "CelestialBody.GetName" ->
+ *   ["CelestialBody.get_Name", "get_CelestialBody.Name"].
+ * (We try the most likely variant first; the second is an extra
+ * fallback in case the kRPC server ever uses a flat "get_X.Y" form,
+ * which historical versions have done for some properties.)
+ */
+function netNameVariants(procedure: string): string[] {
+  const variants: string[] = [];
+  const lastDot = procedure.lastIndexOf('.');
+  if (lastDot < 0) {
+    // Top-level: "GetUT" -> "get_UT"
+    if (procedure.startsWith('Get') && procedure.length > 3) {
+      variants.push(`get_${procedure.slice(3)}`);
+    } else if (procedure.startsWith('Set') && procedure.length > 3) {
+      variants.push(`set_${procedure.slice(3)}`);
+    }
+  } else {
+    // Class-prefixed: "CelestialBody.GetName" -> "CelestialBody.get_Name"
+    const prefix = procedure.slice(0, lastDot);
+    const method = procedure.slice(lastDot + 1);
+    if (method.startsWith('Get') && method.length > 3) {
+      variants.push(`${prefix}.get_${method.slice(3)}`);
+    } else if (method.startsWith('Set') && method.length > 3) {
+      variants.push(`${prefix}.set_${method.slice(3)}`);
+    }
+  }
+  return variants;
+}
+
+export class ServiceCache {
+  /** "SpaceCenter.CelestialBody.GetName" -> ProcedureInfo */
+  private byFullName = new Map<string, ProcedureInfo>();
+  /** "SpaceCenter" -> "SpaceCenter" (just the service name) */
+  private services = new Set<string>();
+  /** "SpaceCenter.VesselType" -> "Ship" (enum name) -> int value */
+  private enumValues = new Map<string, Map<string, number>>();
+  /** "SpaceCenter" -> "VesselType" (enum name) -> Map<name, value> */
+  private enumsByService = new Map<string, Map<string, Map<string, number>>>();
+
+  constructor(raw: RawServicesMessage) {
+    for (const svc of raw.services ?? []) {
+      this.services.add(svc.name);
+      for (const proc of svc.procedures ?? []) {
+        // proc.name already includes the class prefix when applicable
+        // (e.g. "CelestialBody.GetName"), per the kRPC wire format.
+        const info: ProcedureInfo = {
+          service: svc.name,
+          name: proc.name,
+          fullName: `${svc.name}.${proc.name}`,
+          returnType: decodeKrpcType(proc.returnType),
+          returnIsNullable: !!proc.returnIsNullable,
+          parameters: (proc.parameters ?? []).map((p) => ({
+            name: p.name,
+            type: decodeKrpcType(p.type),
+            nullable: !!p.nullable,
+          })),
+        };
+        this.byFullName.set(info.fullName, info);
+      }
+      for (const e of svc.enumerations ?? []) {
+        const m = new Map<string, number>();
+        for (const v of e.values ?? []) {
+          m.set(v.name, v.value);
+        }
+        const fq = `${svc.name}.${e.name}`;
+        this.enumValues.set(fq, m);
+        let inner = this.enumsByService.get(svc.name);
+        if (!inner) {
+          inner = new Map();
+          this.enumsByService.set(svc.name, inner);
+        }
+        inner.set(e.name, m);
+      }
+    }
+  }
+
+  /** All known service names, e.g. ["KRPC", "SpaceCenter", "KerbalAlarmClock", ...]. */
+  serviceNames(): string[] {
+    return [...this.services].sort();
+  }
+
+  /**
+   * All procedure full names in a service, e.g.
+   * ["SpaceCenter.GetUT", "SpaceCenter.CelestialBody.GetName", ...].
+   */
+  proceduresInService(service: string): string[] {
+    const out: string[] = [];
+    for (const info of this.byFullName.values()) {
+      if (info.service === service) out.push(info.fullName);
+    }
+    return out.sort();
+  }
+
+  /**
+   * Look up a procedure by `service.procedure` (e.g. "SpaceCenter.GetUT") or
+   * by the class-prefixed form ("SpaceCenter.CelestialBody.GetName").
+   *
+   * The kRPC server exposes C# properties using .NET naming conventions:
+   * a property `UT` on the SpaceCenter service becomes two procedures,
+   * `get_UT` and `set_UT`. Class properties like `CelestialBody.Name`
+   * become `CelestialBody.get_Name` and `CelestialBody.set_Name`.
+   * We accept the more familiar PascalCase form as a fallback, both
+   * for top-level procedures (GetUT -> get_UT) and class-prefixed
+   * ones (CelestialBody.GetName -> CelestialBody.get_Name).
+   */
+  lookup(service: string, procedure: string): ProcedureLookup {
+    const direct = this.byFullName.get(`${service}.${procedure}`);
+    if (direct) return { found: true, info: direct };
+
+    // PascalCase -> .NET-style fallback. We try both the simple form
+    // (GetUT -> get_UT) and the class-prefixed form
+    // (CelestialBody.GetName -> CelestialBody.get_Name) so user
+    // code can use either convention.
+    for (const variant of netNameVariants(procedure)) {
+      const hit = this.byFullName.get(`${service}.${variant}`);
+      if (hit) return { found: true, info: hit };
+    }
+
+    return { found: false };
+  }
+
+  /**
+   * Resolve an enum value name to its int code. e.g.
+   *   getEnumValue("SpaceCenter", "VesselType", "Ship")  -> 0
+   * Throws if the enum or value is unknown.
+   */
+  getEnumValue(service: string, enumName: string, valueName: string): number {
+    const m = this.enumValues.get(`${service}.${enumName}`);
+    if (!m) {
+      throw new Error(`unknown enum ${service}.${enumName}`);
+    }
+    const v = m.get(valueName);
+    if (v === undefined) {
+      throw new Error(`unknown value ${valueName} for ${service}.${enumName}`);
+    }
+    return v;
+  }
+
+  /**
+   * Inverse: resolve an int code to a value name. Returns null if the
+   * code is not in the enum's range — kRPC may add new values in newer
+   * versions, so callers should be defensive.
+   */
+  getEnumName(
+    service: string,
+    enumName: string,
+    valueCode: number,
+  ): string | null {
+    const m = this.enumValues.get(`${service}.${enumName}`);
+    if (!m) return null;
+    for (const [n, v] of m.entries()) {
+      if (v === valueCode) return n;
+    }
+    return null;
+  }
+
+  /**
+   * All enum value names for an enum, e.g.
+   *   getEnumNames("SpaceCenter", "VesselType")
+   *     -> ["Ship", "Station", "Lander", "Probe", ...]
+   */
+  getEnumNames(service: string, enumName: string): string[] {
+    const m = this.enumValues.get(`${service}.${enumName}`);
+    if (!m) return [];
+    return [...m.keys()].sort();
+  }
+
+  /**
+   * Count the number of distinct procedures across all services.
+   * Useful for tests and diagnostics.
+   */
+  procedureCount(): number {
+    return this.byFullName.size;
+  }
+}

packages/krpc-client/src/types.ts

@@ -0,0 +1,162 @@
+/**
+ * kRPC Type runtime representation.
+ *
+ * kRPC values are encoded on the wire in a custom way that sits on top of
+ * the standard protobuf encoding. Every procedure return / argument carries
+ * a `KrpcType` descriptor that tells the client how to encode/decode the
+ * bytes. The descriptor is itself a protobuf message (KRPC.Type) and is
+ * exchanged via `KRPC.GetServices()` at connect time.
+ *
+ * See: https://krpc.github.io/krpc/communication-protocols/messages.html
+ * and the Python client's `krpc.types` / `krpc.decoder` modules for the
+ * canonical reference implementation.
+ *
+ * TypeCode numeric values match the protobuf enum in krpc.proto:
+ *   0 NONE, 1 DOUBLE, 2 FLOAT, 3 SINT32, 4 SINT64, 5 UINT32, 6 UINT64,
+ *   7 BOOL, 8 STRING, 9 BYTES,
+ *   100 CLASS, 101 ENUMERATION,
+ *   200 EVENT, 201 PROCEDURE_CALL, 202 STREAM, 203 STATUS, 204 SERVICES,
+ *   300 TUPLE, 301 LIST, 302 SET, 303 DICTIONARY.
+ */
+export const TypeCode = {
+  NONE: 0,
+  DOUBLE: 1,
+  FLOAT: 2,
+  SINT32: 3,
+  SINT64: 4,
+  UINT32: 5,
+  UINT64: 6,
+  BOOL: 7,
+  STRING: 8,
+  BYTES: 9,
+  CLASS: 100,
+  ENUMERATION: 101,
+  EVENT: 200,
+  PROCEDURE_CALL: 201,
+  STREAM: 202,
+  STATUS: 203,
+  SERVICES: 204,
+  TUPLE: 300,
+  LIST: 301,
+  SET: 302,
+  DICTIONARY: 303,
+} as const;
+
+export type TypeCodeValue = (typeof TypeCode)[keyof typeof TypeCode];
+
+/**
+ * Decoded form of a kRPC Type message. We don't try to keep the
+ * protobufjs wrapper — the few fields we care about (code, service, name,
+ * types) are copied into this plain object for ergonomic access.
+ */
+export interface KrpcType {
+  code: TypeCodeValue;
+  /** For CLASS / ENUMERATION: the service that defines the type. */
+  service: string;
+  /** For CLASS / ENUMERATION: the class/enum name. */
+  name: string;
+  /**
+   * Nested types. Used by collections (LIST<T>, SET<T>, TUPLE<A,B>, DICT<K,V>).
+   * The semantics depend on the code:
+   *   LIST / SET:  types[0] is the element type
+   *   TUPLE:       types[i] is the i-th element type
+   *   DICTIONARY:  types[0] is the key type, types[1] is the value type
+   * For CLASS / ENUMERATION: empty.
+   */
+  types: KrpcType[];
+}
+
+/**
+ * Decode a kRPC Type protobuf message into our plain KrpcType shape.
+ * Exposed so callers (e.g. the service cache) can transform the
+ * GetServices() response into a useful index.
+ */
+export interface RawKrpcTypeMessage {
+  code: number;
+  service: string;
+  name: string;
+  types: RawKrpcTypeMessage[];
+}
+
+/**
+ * Decode a kRPC Type protobuf message into our plain KrpcType shape.
+ *
+ * Returns a NONE-type KrpcType if `raw` is null/undefined or doesn't
+ * have a `code` field — which happens for procedures with no return
+ * value (the kRPC server omits the `return_type` field). We treat that
+ * as the NONE type code (0) rather than throwing.
+ */
+export function decodeKrpcType(raw: RawKrpcTypeMessage | null | undefined): KrpcType {
+  if (!raw || typeof raw.code !== 'number') {
+    return {
+      code: 0 as TypeCodeValue, // NONE
+      service: '',
+      name: '',
+      types: [],
+    };
+  }
+  return {
+    code: raw.code as TypeCodeValue,
+    service: raw.service ?? '',
+    name: raw.name ?? '',
+    types: (raw.types ?? []).map(decodeKrpcType),
+  };
+}
+
+/**
+ * Human-readable name for a typecode. Used in error messages and for
+ * debugging. Not used in wire encoding.
+ */
+export function typeName(t: KrpcType): string {
+  switch (t.code) {
+    case TypeCode.NONE:
+      return 'None';
+    case TypeCode.DOUBLE:
+      return 'double';
+    case TypeCode.FLOAT:
+      return 'float';
+    case TypeCode.SINT32:
+      return 'sint32';
+    case TypeCode.SINT64:
+      return 'sint64';
+    case TypeCode.UINT32:
+      return 'uint32';
+    case TypeCode.UINT64:
+      return 'uint64';
+    case TypeCode.BOOL:
+      return 'bool';
+    case TypeCode.STRING:
+      return 'string';
+    case TypeCode.BYTES:
+      return 'bytes';
+    case TypeCode.CLASS:
+      return `${t.service}.${t.name}`;
+    case TypeCode.ENUMERATION:
+      return `${t.service}.${t.name}`;
+    case TypeCode.EVENT:
+      return 'Event';
+    case TypeCode.PROCEDURE_CALL:
+      return 'ProcedureCall';
+    case TypeCode.STREAM:
+      return 'Stream';
+    case TypeCode.STATUS:
+      return 'Status';
+    case TypeCode.SERVICES:
+      return 'Services';
+    case TypeCode.TUPLE: {
+      const inner = t.types.map(typeName).join(', ');
+      return `(${inner})`;
+    }
+    case TypeCode.LIST:
+      return `list<${t.types[0] ? typeName(t.types[0]) : '?'}>`;
+    case TypeCode.SET:
+      return `set<${t.types[0] ? typeName(t.types[0]) : '?'}>`;
+    case TypeCode.DICTIONARY: {
+      const k = t.types[0] ? typeName(t.types[0]) : '?';
+      const v = t.types[1] ? typeName(t.types[1]) : '?';
+      return `dict<${k}, ${v}>`;
+    }
+    default:
+      return `code=${t.code}`;
+  }
+}

packages/krpc-client/tests/connection.test.ts

@@ -0,0 +1,68 @@
+import { describe, it, expect } from 'vitest';
+import { Buffer } from 'node:buffer';
+import { encodeVarint, decodeVarint } from '../src/connection.js';
+
+describe('varint encoding', () => {
+  it('round-trips small numbers', () => {
+    for (const n of [0, 1, 5, 100, 127]) {
+      const encoded = encodeVarint(n);
+      const [decoded, consumed] = decodeVarint(encoded);
+      expect(decoded).toBe(n);
+      expect(consumed).toBe(encoded.length);
+    }
+  });
+
+  it('round-trips numbers requiring 2 bytes', () => {
+    for (const n of [128, 200, 16383, 16384, 100_000]) {
+      const encoded = encodeVarint(n);
+      const [decoded, consumed] = decodeVarint(encoded);
+      expect(decoded).toBe(n);
+      expect(consumed).toBe(encoded.length);
+    }
+  });
+
+  it('round-trips numbers requiring 4-5 bytes', () => {
+    for (const n of [2 ** 20, 2 ** 28, 2 ** 31 - 1, 2 ** 32]) {
+      const encoded = encodeVarint(n);
+      const [decoded, consumed] = decodeVarint(encoded);
+      expect(decoded).toBe(n);
+      expect(consumed).toBe(encoded.length);
+    }
+  });
+
+  it('encodes correctly per the protobuf spec', () => {
+    // Reference values from the protobuf documentation
+    expect([...encodeVarint(0)]).toEqual([0x00]);
+    expect([...encodeVarint(1)]).toEqual([0x01]);
+    expect([...encodeVarint(127)]).toEqual([0x7f]);
+    expect([...encodeVarint(128)]).toEqual([0x80, 0x01]);
+    expect([...encodeVarint(300)]).toEqual([0xac, 0x02]);
+  });
+
+  it('decodes from a multi-byte buffer correctly', () => {
+    // decodeVarint should stop at the varint boundary
+    const buf = Buffer.concat([encodeVarint(42), Buffer.from([0xff, 0xee])]);
+    const [decoded, consumed] = decodeVarint(buf);
+    expect(decoded).toBe(42);
+    expect(consumed).toBe(1); // only the first byte was the varint
+  });
+
+  it('rejects negative numbers', () => {
+    expect(() => encodeVarint(-1)).toThrow();
+  });
+});
+
+describe('varint edge cases', () => {
+  it('decodes 0', () => {
+    const [v, c] = decodeVarint(Buffer.from([0]));
+    expect(v).toBe(0);
+    expect(c).toBe(1);
+  });
+
+  it('decodes max uint32', () => {
+    const n = 0xffffffff;
+    const [v, c] = decodeVarint(encodeVarint(n));
+    expect(v).toBe(n);
+    expect(c).toBe(encodeVarint(n).length);
+  });
+});

packages/krpc-client/tests/decoder.test.ts

@@ -0,0 +1,346 @@
+import { describe, it, expect } from 'vitest';
+import protobuf from 'protobufjs';
+import {
+  decodeValue,
+  encodeValue,
+  decodeDouble,
+  decodeFloat,
+  decodeSint32,
+  decodeUint32,
+  decodeUint64,
+  decodeBool,
+  decodeString,
+  decodeBytes,
+  decodeList,
+  decodeTuple,
+  decodeDictionary,
+  decodeKrpcList,
+} from '../src/decoder.js';
+import { TypeCode, type KrpcType } from '../src/types.js';
+import { MESSAGE_TYPES, KRPC } from '../src/schema.js';
+
+const T = (t: Partial<KrpcType>): KrpcType => ({
+  code: t.code ?? 0,
+  service: t.service ?? '',
+  name: t.name ?? '',
+  types: t.types ?? [],
+});
+
+// We need a small fake "TYPE" registry for the tests so the decoder
+// can find List / Tuple / Dictionary / Status by name. We can use the
+// real MESSAGE_TYPES for the actual system messages.
+const REG = MESSAGE_TYPES;
+
+describe('primitive decoders', () => {
+  it('decodes a double (8-byte little-endian)', () => {
+    expect(decodeDouble(new Uint8Array(new Float64Array([3.14]).buffer))).toBeCloseTo(3.14, 10);
+    expect(decodeDouble(new Uint8Array(new Float64Array([-0]).buffer))).toBe(-0);
+    expect(decodeDouble(new Uint8Array(new Float64Array([0]).buffer))).toBe(0);
+    expect(decodeDouble(new Uint8Array(new Float64Array([1e30]).buffer))).toBe(1e30);
+  });
+
+  it('decodes a float (4-byte little-endian)', () => {
+    expect(decodeFloat(new Uint8Array(new Float32Array([2.5]).buffer))).toBeCloseTo(2.5, 5);
+  });
+
+  it('decodes a sint32 (zigzag varint)', () => {
+    // 0 -> 0, 1 -> 2, -1 -> 1, 2 -> 4, -2 -> 3
+    expect(decodeSint32(new Uint8Array([0]))).toBe(0);
+    expect(decodeSint32(new Uint8Array([2]))).toBe(1);
+    expect(decodeSint32(new Uint8Array([1]))).toBe(-1);
+    expect(decodeSint32(new Uint8Array([4]))).toBe(2);
+    expect(decodeSint32(new Uint8Array([3]))).toBe(-2);
+  });
+
+  it('decodes a uint32 (varint)', () => {
+    expect(decodeUint32(new Uint8Array([0]))).toBe(0);
+    expect(decodeUint32(new Uint8Array([0x7f]))).toBe(127);
+    expect(decodeUint32(new Uint8Array([0x80, 0x01]))).toBe(128);
+  });
+
+  it('decodes a uint64 to BigInt (preserves > 2^53)', () => {
+    // 2^53 + 1 exceeds Number.MAX_SAFE_INTEGER. Verify the decoder
+    // produces the exact BigInt. Hand-varint for 2^53+1:
+    //   7-bit groups, LSB first: 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x10
+    //   (bit 53 = position 4 in the last group = 0b0010000 = 0x10)
+    const big = 0x20_0000_0000_0001n; // 2^53 + 1
+    const bytes = new Uint8Array([0x81, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x10]);
+    expect(decodeUint64(bytes)).toBe(big);
+  });
+
+  it('decodes a bool', () => {
+    expect(decodeBool(new Uint8Array([0]))).toBe(false);
+    expect(decodeBool(new Uint8Array([1]))).toBe(true);
+    expect(decodeBool(new Uint8Array([0xff]))).toBe(true);
+  });
+
+  it('decodes a string', () => {
+    const utf8 = new TextEncoder().encode('Kerbin');
+    const buf = new Uint8Array([utf8.length, ...utf8]);
+    expect(decodeString(buf)).toBe('Kerbin');
+  });
+
+  it('decodes a string with non-ASCII characters', () => {
+    const utf8 = new TextEncoder().encode('日本語');
+    const buf = new Uint8Array([utf8.length, ...utf8]);
+    expect(decodeString(buf)).toBe('日本語');
+  });
+
+  it('decodes bytes', () => {
+    const payload = new Uint8Array([0xde, 0xad, 0xbe, 0xef]);
+    const buf = new Uint8Array([payload.length, ...payload]);
+    expect(decodeBytes(buf)).toEqual(payload);
+  });
+});
+
+describe('decodeValue dispatcher', () => {
+  it('decodes DOUBLE', () => {
+    const bytes = new Uint8Array(new Float64Array([2.71828]).buffer);
+    const out = decodeValue(T({ code: TypeCode.DOUBLE }), bytes);
+    expect(out).toBeCloseTo(2.71828, 5);
+  });
+
+  it('decodes STRING', () => {
+    const utf8 = new TextEncoder().encode('Mun');
+    const bytes = new Uint8Array([utf8.length, ...utf8]);
+    expect(decodeValue(T({ code: TypeCode.STRING }), bytes)).toBe('Mun');
+  });
+
+  it('decodes CLASS object id (non-null)', () => {
+    // 42 as varint
+    const id = decodeValue(T({ code: TypeCode.CLASS, service: 'SpaceCenter', name: 'Vessel' }), new Uint8Array([42]));
+    expect(id).toBe(42n);
+  });
+
+  it('decodes CLASS object id (null when 0)', () => {
+    expect(
+      decodeValue(
+        T({ code: TypeCode.CLASS, service: 'SpaceCenter', name: 'Vessel' }),
+        new Uint8Array([0]),
+      ),
+    ).toBeNull();
+  });
+
+  it('decodes ENUMERATION as a sint32', () => {
+    expect(
+      decodeValue(
+        T({ code: TypeCode.ENUMERATION, service: 'SpaceCenter', name: 'VesselType' }),
+        new Uint8Array([0]), // Ship
+      ),
+    ).toBe(0);
+  });
+
+  it('decodes NONE as null', () => {
+    expect(decodeValue(T({ code: TypeCode.NONE }), new Uint8Array(0))).toBeNull();
+  });
+
+  it('throws on unknown type code', () => {
+    expect(() => decodeValue(T({ code: 9999 }), new Uint8Array(0))).toThrow(/unknown TypeCode/);
+  });
+});
+
+describe('collection decoders', () => {
+  it('decodes a list of doubles', () => {
+    // Construct a KRPC.List message manually:
+    //   items[0] = 8 bytes for double 1.0
+    //   items[1] = 8 bytes for double 2.5
+    const d1 = new Uint8Array(new Float64Array([1.0]).buffer);
+    const d2 = new Uint8Array(new Float64Array([2.5]).buffer);
+    const listMsg = KRPC.List.create({ items: [d1, d2] });
+    const listBytes = KRPC.List.encode(listMsg).finish();
+    const out = decodeList(
+      T({ code: TypeCode.LIST, types: [T({ code: TypeCode.DOUBLE })] }),
+      listBytes,
+      REG,
+    );
+    expect(out).toEqual([1.0, 2.5]);
+  });
+
+  it('decodes a list of strings', () => {
+    const enc = (s: string): Uint8Array => {
+      const utf8 = new TextEncoder().encode(s);
+      return new Uint8Array([utf8.length, ...utf8]);
+    };
+    const listMsg = KRPC.List.create({ items: [enc('Kerbin'), enc('Mun')] });
+    const listBytes = KRPC.List.encode(listMsg).finish();
+    const out = decodeList(
+      T({ code: TypeCode.LIST, types: [T({ code: TypeCode.STRING })] }),
+      listBytes,
+      REG,
+    );
+    expect(out).toEqual(['Kerbin', 'Mun']);
+  });
+
+  it('decodes an empty list', () => {
+    const listMsg = KRPC.List.create({ items: [] });
+    const listBytes = KRPC.List.encode(listMsg).finish();
+    const out = decodeList(
+      T({ code: TypeCode.LIST, types: [T({ code: TypeCode.STRING })] }),
+      listBytes,
+      REG,
+    );
+    expect(out).toEqual([]);
+  });
+
+  it('decodes a null list as null', () => {
+    const out = decodeList(
+      T({ code: TypeCode.LIST, types: [T({ code: TypeCode.STRING })] }),
+      new Uint8Array([0]),
+      REG,
+    );
+    expect(out).toBeNull();
+  });
+
+  it('decodes a list of CLASS as a bigint array', () => {
+    // items[0] = 7, items[1] = 0 (null)
+    const listMsg = KRPC.List.create({ items: [new Uint8Array([7]), new Uint8Array([0])] });
+    const listBytes = KRPC.List.encode(listMsg).finish();
+    const out = decodeList(
+      T({
+        code: TypeCode.LIST,
+        types: [T({ code: TypeCode.CLASS, service: 'SpaceCenter', name: 'CelestialBody' })],
+      }),
+      listBytes,
+      REG,
+    );
+    expect(out).toEqual([7n, null]);
+  });
+
+  it('decodes a tuple of mixed types', () => {
+    // tuple: (string "Kerbin", double 0.5)
+    const utf8 = new TextEncoder().encode('Kerbin');
+    const sBytes = new Uint8Array([utf8.length, ...utf8]);
+    const dBytes = new Uint8Array(new Float64Array([0.5]).buffer);
+    const tupleMsg = KRPC.Tuple.create({ items: [sBytes, dBytes] });
+    const tupleBytes = KRPC.Tuple.encode(tupleMsg).finish();
+    const out = decodeTuple(
+      T({
+        code: TypeCode.TUPLE,
+        types: [T({ code: TypeCode.STRING }), T({ code: TypeCode.DOUBLE })],
+      }),
+      tupleBytes,
+      REG,
+    );
+    expect(out).toEqual(['Kerbin', 0.5]);
+  });
+
+  it('decodes a dictionary of string -> double', () => {
+    const utf8 = new TextEncoder().encode('mu');
+    const sBytes = new Uint8Array([utf8.length, ...utf8]);
+    const dBytes = new Uint8Array(new Float64Array([3.53e12]).buffer);
+    const dictMsg = KRPC.Dictionary.create({
+      entries: [{ key: sBytes, value: dBytes }],
+    });
+    const dictBytes = KRPC.Dictionary.encode(dictMsg).finish();
+    const out = decodeDictionary(
+      T({
+        code: TypeCode.DICTIONARY,
+        types: [T({ code: TypeCode.STRING }), T({ code: TypeCode.DOUBLE })],
+      }),
+      dictBytes,
+      REG,
+    );
+    expect(out.get('mu')).toBe(3.53e12);
+  });
+
+  it('decodes a null dictionary as null', () => {
+    const out = decodeDictionary(
+      T({
+        code: TypeCode.DICTIONARY,
+        types: [T({ code: TypeCode.STRING }), T({ code: TypeCode.DOUBLE })],
+      }),
+      new Uint8Array([0]),
+      REG,
+    );
+    expect(out).toBeNull();
+  });
+
+  it('exposes a low-level decodeKrpcList for testing', () => {
+    const listMsg = KRPC.List.create({ items: [new Uint8Array([1, 2, 3])] });
+    const bytes = KRPC.List.encode(listMsg).finish();
+    const out = decodeKrpcList(bytes, KRPC.List);
+    // protobufjs returns Node Buffers (which extend Uint8Array). Compare
+    // the underlying bytes so this works regardless of wrapper class.
+    expect(out).toHaveLength(1);
+    expect(Array.from(out[0] as Uint8Array)).toEqual([1, 2, 3]);
+  });
+});
+
+describe('encodeValue (round-trips)', () => {
+  it('encodes a double', () => {
+    const bytes = encodeValue(T({ code: TypeCode.DOUBLE }), 1.5);
+    expect(decodeValue(T({ code: TypeCode.DOUBLE }), bytes)).toBe(1.5);
+  });
+
+  it('encodes a string', () => {
+    const bytes = encodeValue(T({ code: TypeCode.STRING }), 'Kerbol');
+    expect(decodeValue(T({ code: TypeCode.STRING }), bytes)).toBe('Kerbol');
+  });
+
+  it('encodes a CLASS object id', () => {
+    const bytes = encodeValue(
+      T({ code: TypeCode.CLASS, service: 'SpaceCenter', name: 'Vessel' }),
+      42n,
+    );
+    expect(decodeValue(T({ code: TypeCode.CLASS, service: 'SpaceCenter', name: 'Vessel' }), bytes)).toBe(42n);
+  });
+
+  it('encodes a null CLASS as id=0', () => {
+    const bytes = encodeValue(
+      T({ code: TypeCode.CLASS, service: 'SpaceCenter', name: 'Vessel' }),
+      null,
+    );
+    expect(bytes).toEqual(new Uint8Array([0]));
+  });
+
+  it('encodes an ENUMERATION', () => {
+    const bytes = encodeValue(
+      T({ code: TypeCode.ENUMERATION, service: 'SpaceCenter', name: 'VesselType' }),
+      3, // Probe
+    );
+    expect(
+      decodeValue(
+        T({ code: TypeCode.ENUMERATION, service: 'SpaceCenter', name: 'VesselType' }),
+        bytes,
+      ),
+    ).toBe(3);
+  });
+
+  it('encodes a list of doubles', () => {
+    const bytes = encodeValue(
+      T({ code: TypeCode.LIST, types: [T({ code: TypeCode.DOUBLE })] }),
+      [1.0, 2.0, 3.0],
+      REG,
+    );
+    const out = decodeValue(
+      T({ code: TypeCode.LIST, types: [T({ code: TypeCode.DOUBLE })] }),
+      bytes,
+      REG,
+    );
+    expect(out).toEqual([1.0, 2.0, 3.0]);
+  });
+
+  it('encodes a uint64 BigInt', () => {
+    const id = 0x1_0000_0000n; // 2^32
+    const bytes = encodeValue(T({ code: TypeCode.UINT64 }), id);
+    expect(decodeValue(T({ code: TypeCode.UINT64 }), bytes)).toBe(id);
+  });
+
+  it('encodes a bool', () => {
+    expect(decodeValue(T({ code: TypeCode.BOOL }), encodeValue(T({ code: TypeCode.BOOL }), true))).toBe(true);
+    expect(decodeValue(T({ code: TypeCode.BOOL }), encodeValue(T({ code: TypeCode.BOOL }), false))).toBe(false);
+  });
+
+  it('rejects SET (not implemented)', () => {
+    expect(() =>
+      encodeValue(T({ code: TypeCode.SET, types: [T({ code: TypeCode.STRING })] }), new Set(), REG),
+    ).toThrow(/SET not implemented/);
+  });
+});
+
+// Suppress unused-warning for the TYPE const helper by using it once.
+const _checkTypeHelper: KrpcType = T({ code: TypeCode.STRING });
+void _checkTypeHelper;
+// Also pin the protobufjs default import to confirm we still have it.
+const _pb: typeof protobuf = protobuf;
+void _pb;

packages/krpc-client/tests/integration.test.ts

@@ -0,0 +1,112 @@
+/**
+ * Integration test: drive the wire format with raw sockets to exercise
+ * the same code paths that KRPCClient uses internally.
+ *
+ * We don't mock a full kRPC server (that's a lot of state-machine work
+ * for a single test); the KRPCClient class is verified manually
+ * (the file imports cleanly + we can connect to a real kRPC server
+ * once you have KSP running).
+ */
+import { describe, it, expect } from 'vitest';
+import * as net from 'node:net';
+import { Buffer } from 'node:buffer';
+import { KRPC, encodeMessage, decodeMessage } from '../src/schema.js';
+import { sendMessage, recvMessage, encodeVarint } from '../src/connection.js';
+
+describe('wire format round trip with raw sockets', () => {
+  it('exchanges ConnectionRequest and ConnectionResponse', async () => {
+    const server = net.createServer((socket) => {
+      void (async () => {
+        const req = await recvMessage<{ type: number; clientName: string }>(
+          socket,
+          KRPC.ConnectionRequest,
+        );
+        expect(req.type).toBe(0); // RPC
+        expect(req.clientName).toBe('test');
+
+        const resp = encodeMessage(KRPC.ConnectionResponse, {
+          status: 0,
+          message: '',
+          clientIdentifier: Buffer.from('test-client-id'),
+        });
+        socket.write(Buffer.concat([encodeVarint(resp.length), resp]));
+        await new Promise((r) => setTimeout(r, 50));
+        socket.destroy();
+      })();
+    });
+
+    await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve));
+    const port = (server.address() as net.AddressInfo).port;
+
+    const client = net.createConnection({ host: '127.0.0.1', port });
+    await new Promise<void>((resolve) => client.once('connect', () => resolve()));
+
+    // Handshake
+    sendMessage(client, KRPC.ConnectionRequest, { type: 'RPC', clientName: 'test' });
+    const resp = await recvMessage<{ status: number; clientIdentifier: Uint8Array }>(
+      client,
+      KRPC.ConnectionResponse,
+    );
+    expect(resp.status).toBe(0);
+    expect(Buffer.from(resp.clientIdentifier).toString()).toBe('test-client-id');
+
+    client.destroy();
+    await new Promise<void>((resolve) => server.close(() => resolve()));
+  });
+
+  it('exchanges a Request with a Response carrying a Status return value', async () => {
+    const server = net.createServer((socket) => {
+      void (async () => {
+        // Handshake first
+        const req = await recvMessage<{ type: number }>(socket, KRPC.ConnectionRequest);
+        expect(req.type).toBe(0);
+        const resp = encodeMessage(KRPC.ConnectionResponse, {
+          status: 0,
+          message: '',
+          clientIdentifier: Buffer.from('x'),
+        });
+        socket.write(Buffer.concat([encodeVarint(resp.length), resp]));
+
+        // Now handle the Request
+        const statusReq = await recvMessage<{ calls: { service: string; procedure: string }[] }>(
+          socket,
+          KRPC.Request,
+        );
+        expect(statusReq.calls.length).toBe(1);
+        expect(statusReq.calls[0]!.service).toBe('KRPC');
+        expect(statusReq.calls[0]!.procedure).toBe('GetStatus');
+
+        const status = encodeMessage(KRPC.Status, {
+          version: '0.5.0',
+          bytesRead: 100n,
+          bytesWritten: 50n,
+          bytesReadRate: 1.0,
+          bytesWrittenRate: 0.5,
+        });
+        const respMsg = encodeMessage(KRPC.Response, { results: [{ value: status }] });
+        socket.write(Buffer.concat([encodeVarint(respMsg.length), respMsg]));
+        await new Promise((r) => setTimeout(r, 50));
+        socket.destroy();
+      })();
+    });
+
+    await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve));
+    const port = (server.address() as net.AddressInfo).port;
+
+    const client = net.createConnection({ host: '127.0.0.1', port });
+    await new Promise<void>((resolve) => client.once('connect', () => resolve()));
+
+    sendMessage(client, KRPC.ConnectionRequest, { type: 'RPC', clientName: 'test' });
+    await recvMessage(client, KRPC.ConnectionResponse);
+
+    sendMessage(client, KRPC.Request, {
+      calls: [{ service: 'KRPC', procedure: 'GetStatus' }],
+    });
+    const callResp = await recvMessage<{ results: { value: Uint8Array }[] }>(client, KRPC.Response);
+    const status = decodeMessage<{ version: string }>(KRPC.Status, callResp.results[0]!.value);
+    expect(status.version).toBe('0.5.0');
+
+    client.destroy();
+    await new Promise<void>((resolve) => server.close(() => resolve()));
+  });
+});

packages/krpc-client/tests/service-client.test.ts

@@ -0,0 +1,383 @@
+/**
+ * End-to-end test of KrpcServices with a tiny mock kRPC server.
+ *
+ * We start a real TCP server that:
+ *   1. Accepts the RPC + stream handshakes
+ *   2. Handles a small whitelist of procedure calls by responding
+ *      with hand-encoded values
+ *
+ * The test then drives a real KRPCClient + KrpcServices pair through
+ * the same wire format a real kRPC server uses, and verifies the
+ * decoded values match the hand-encoded responses.
+ *
+ * For the server side we use the same SocketReader-based pattern that
+ * the client uses, so the two sides share framing semantics.
+ */
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import * as net from 'node:net';
+import { Buffer } from 'node:buffer';
+import { KRPC, encodeMessage } from '../src/schema.js';
+import { KRPCClient } from '../src/client.js';
+import { loadServices, KrpcServices } from '../src/service-client.js';
+import { encodeVarint, recvMessage, sendMessage } from '../src/connection.js';
+import {
+  encodeDouble,
+  encodeString,
+  encodeUint64,
+  encodeSint32,
+} from '../src/_test-encode.js';
+
+/** Mock services message that the server will hand back on GetServices. */
+const MOCK_SERVICES_RAW = {
+  services: [
+    {
+      name: 'KRPC',
+      procedures: [
+        {
+          name: 'GetStatus',
+          parameters: [],
+          returnType: { code: 203, service: '', name: '', types: [] },
+          returnIsNullable: false,
+        },
+        {
+          name: 'GetServices',
+          parameters: [],
+          returnType: { code: 204, service: '', name: '', types: [] },
+          returnIsNullable: false,
+        },
+      ],
+      classes: [],
+      enumerations: [],
+    },
+    {
+      name: 'SpaceCenter',
+      procedures: [
+        {
+          name: 'GetUT',
+          parameters: [],
+          returnType: { code: 1, service: '', name: '', types: [] },
+          returnIsNullable: false,
+        },
+        {
+          name: 'GetActiveVessel',
+          parameters: [],
+          returnType: { code: 100, service: 'SpaceCenter', name: 'Vessel', types: [] },
+          returnIsNullable: false,
+        },
+        {
+          name: 'GetBodies',
+          parameters: [],
+          returnType: {
+            code: 301,
+            service: '',
+            name: '',
+            types: [{ code: 100, service: 'SpaceCenter', name: 'CelestialBody', types: [] }],
+          },
+          returnIsNullable: false,
+        },
+        {
+          name: 'CelestialBody.GetName',
+          parameters: [
+            {
+              name: 'self',
+              type: { code: 100, service: 'SpaceCenter', name: 'CelestialBody', types: [] },
+              nullable: false,
+            },
+          ],
+          returnType: { code: 8, service: '', name: '', types: [] },
+          returnIsNullable: false,
+        },
+        {
+          name: 'Vessel.GetName',
+          parameters: [
+            {
+              name: 'self',
+              type: { code: 100, service: 'SpaceCenter', name: 'Vessel', types: [] },
+              nullable: false,
+            },
+          ],
+          returnType: { code: 8, service: '', name: '', types: [] },
+          returnIsNullable: false,
+        },
+        {
+          name: 'Vessel.GetType',
+          parameters: [
+            {
+              name: 'self',
+              type: { code: 100, service: 'SpaceCenter', name: 'Vessel', types: [] },
+              nullable: false,
+            },
+          ],
+          returnType: { code: 101, service: 'SpaceCenter', name: 'VesselType', types: [] },
+          returnIsNullable: false,
+        },
+      ],
+      classes: [{ name: 'CelestialBody' }, { name: 'Vessel' }, { name: 'Orbit' }],
+      enumerations: [
+        {
+          name: 'VesselType',
+          values: [
+            { name: 'Ship', value: 0 },
+            { name: 'Probe', value: 3 },
+          ],
+        },
+      ],
+    },
+  ],
+};
+
+async function freePort(): Promise<number> {
+  return new Promise<number>((resolve, reject) => {
+    const srv = net.createServer();
+    srv.unref();
+    srv.on('error', reject);
+    srv.listen(0, '127.0.0.1', () => {
+      const addr = srv.address();
+      if (addr && typeof addr === 'object') {
+        const p = addr.port;
+        srv.close(() => resolve(p));
+      } else {
+        srv.close(() => reject(new Error('no addr')));
+      }
+    });
+  });
+}
+
+function replyWithValue(socket: net.Socket, value: Uint8Array): void {
+  const resultMsg = KRPC.ProcedureResult.create({
+    value: Buffer.from(value),
+  });
+  const respMsg = KRPC.Response.create({ results: [resultMsg] });
+  const payload = Buffer.from(KRPC.Response.encode(respMsg).finish());
+  sendMessage(socket, KRPC.Response, { results: [resultMsg] });
+  void payload;
+}
+
+function replyWithError(socket: net.Socket, name: string, description: string): void {
+  const errMsg = KRPC.Error.create({ service: 'Test', name, description });
+  const resultMsg = KRPC.ProcedureResult.create({ error: errMsg, value: Buffer.from([]) });
+  sendMessage(socket, KRPC.Response, { results: [resultMsg] });
+}
+
+interface MockServer {
+  rpcPort: number;
+  streamPort: number;
+  close: () => Promise<void>;
+  stub: (
+    service: string,
+    procedure: string,
+    handler: (args: Uint8Array[]) => Uint8Array,
+  ) => void;
+  /** Counts the number of calls received for (service, procedure). */
+  callCount: (service: string, procedure: string) => number;
+  /** Captured arguments of the last call to (service, procedure). */
+  lastArgs: (service: string, procedure: string) => Uint8Array[];
+}
+
+async function startMockServer(): Promise<MockServer> {
+  const rpcPort = await freePort();
+  const streamPort = await freePort();
+  const stubs = new Map<string, (args: Uint8Array[]) => Uint8Array>();
+  const counts = new Map<string, number>();
+  const lastArgsMap = new Map<string, Uint8Array[]>();
+
+  const stub = (svc: string, proc: string, handler: (args: Uint8Array[]) => Uint8Array) => {
+    stubs.set(`${svc}.${proc}`, handler);
+  };
+
+  // Default stubs
+  stub('KRPC', 'GetServices', () => {
+    const servicesMsg = KRPC.Services.create(MOCK_SERVICES_RAW);
+    return new Uint8Array(KRPC.Services.encode(servicesMsg).finish());
+  });
+  stub('KRPC', 'GetStatus', () => {
+    const statusMsg = KRPC.Status.create({ version: 'test' });
+    return new Uint8Array(KRPC.Status.encode(statusMsg).finish());
+  });
+  stub('SpaceCenter', 'GetUT', () => encodeDouble(4_700_000.5));
+
+  // ── RPC server ─────────────────────────────────────────────────────
+  const rpcServer = net.createServer((socket) => {
+    void (async () => {
+      try {
+        // 1. Handshake
+        const req = await recvMessage<{ type: number; clientName: string }>(
+          socket,
+          KRPC.ConnectionRequest,
+        );
+        if (req.type !== 0) {
+          socket.destroy();
+          return;
+        }
+        sendMessage(socket, KRPC.ConnectionResponse, {
+          status: 0,
+          message: '',
+          clientIdentifier: Buffer.from('test-client'),
+        });
+
+        // 2. Procedure loop
+        while (!socket.destroyed) {
+          let callReq: {
+            calls: { service: string; procedure: string; arguments?: { value: Uint8Array }[] }[];
+          };
+          try {
+            callReq = await recvMessage(socket, KRPC.Request);
+          } catch {
+            return;
+          }
+          const call = callReq.calls[0];
+          if (!call) {
+            replyWithError(socket, 'Malformed', 'no call');
+            continue;
+          }
+          const key = `${call.service}.${call.procedure}`;
+          counts.set(key, (counts.get(key) ?? 0) + 1);
+          const args = (call.arguments ?? []).map((a) => new Uint8Array(a.value));
+          lastArgsMap.set(key, args);
+          const handler = stubs.get(key);
+          if (!handler) {
+            replyWithError(socket, 'UnknownProcedure', `${key} not stubbed`);
+            continue;
+          }
+          try {
+            const value = handler(args);
+            replyWithValue(socket, value);
+          } catch (e) {
+            replyWithError(socket, 'HandlerError', String(e));
+          }
+        }
+      } catch {
+        if (!socket.destroyed) socket.destroy();
+      }
+    })();
+  });
+  await new Promise<void>((resolve) => rpcServer.listen(rpcPort, '127.0.0.1', resolve));
+
+  // ── Stream server (handshake only, then idle) ─────────────────────
+  const streamServer = net.createServer((socket) => {
+    void (async () => {
+      try {
+        const req = await recvMessage<{ type: number; clientIdentifier: Uint8Array }>(
+          socket,
+          KRPC.ConnectionRequest,
+        );
+        if (req.type !== 1) {
+          socket.destroy();
+          return;
+        }
+        sendMessage(socket, KRPC.ConnectionResponse, { status: 0, message: '' });
+        // Keep alive
+        await new Promise(() => undefined);
+      } catch {
+        socket.destroy();
+      }
+    })();
+  });
+  await new Promise<void>((resolve) => streamServer.listen(streamPort, '127.0.0.1', resolve));
+
+  return {
+    rpcPort,
+    streamPort,
+    stub,
+    callCount: (svc, proc) => counts.get(`${svc}.${proc}`) ?? 0,
+    lastArgs: (svc, proc) => lastArgsMap.get(`${svc}.${proc}`) ?? [],
+    close: () =>
+      new Promise<void>((resolve) => {
+        rpcServer.close(() => {
+          streamServer.close(() => resolve());
+        });
+      }),
+  };
+}
+
+describe('KrpcServices against a mock kRPC server', () => {
+  let server: MockServer;
+  let client: KRPCClient;
+  let services: KrpcServices;
+
+  beforeAll(async () => {
+    server = await startMockServer();
+    client = new KRPCClient({
+      host: '127.0.0.1',
+      rpcPort: server.rpcPort,
+      streamPort: server.streamPort,
+      clientName: 'test',
+    });
+    await client.connect();
+    const loaded = await loadServices(client);
+    services = loaded.services;
+  }, 10_000);
+
+  afterAll(async () => {
+    await client.close();
+    await server.close();
+  });
+
+  it('lists services', () => {
+    const names = services.getCache().serviceNames();
+    expect(names).toContain('KRPC');
+    expect(names).toContain('SpaceCenter');
+  });
+
+  it('looks up the GetUT procedure', () => {
+    const r = services.getCache().lookup('SpaceCenter', 'GetUT');
+    expect(r.found).toBe(true);
+  });
+
+  it('invokes SpaceCenter.GetUT and decodes as double', async () => {
+    const ut = await services.invoke<number>('SpaceCenter', 'GetUT');
+    expect(ut).toBe(4_700_000.5);
+  });
+
+  it('invokes SpaceCenter.GetBodies and decodes a list of class ids', async () => {
+    server.stub('SpaceCenter', 'GetBodies', () => {
+      const items = [encodeUint64(1n), encodeUint64(2n), encodeUint64(3n)];
+      const listMsg = KRPC.List.create({ items });
+      return new Uint8Array(KRPC.List.encode(listMsg).finish());
+    });
+    const ids = await services.invoke<bigint[]>('SpaceCenter', 'GetBodies');
+    expect(ids).toEqual([1n, 2n, 3n]);
+  });
+
+  it('invokes a class method and decodes the string return', async () => {
+    server.stub('SpaceCenter', 'CelestialBody.GetName', () => encodeString('Kerbin'));
+    const name = await services.invoke<string>('SpaceCenter', 'CelestialBody.GetName', 42n);
+    expect(name).toBe('Kerbin');
+  });
+
+  it('rejects an unknown procedure', async () => {
+    await expect(
+      services.invoke('SpaceCenter', 'GetNothing'),
+    ).rejects.toThrow(/procedure not found/);
+  });
+
+  it('rejects a wrong number of arguments', async () => {
+    await expect(
+      services.invoke('SpaceCenter', 'GetBodies', 1n, 2n),
+    ).rejects.toThrow(/wrong number of arguments/);
+  });
+
+  it('decodes an enum return value', async () => {
+    server.stub('SpaceCenter', 'Vessel.GetType', () => encodeSint32(3));
+    const t = await services.invoke<number>('SpaceCenter', 'Vessel.GetType', 7n);
+    expect(t).toBe(3);
+  });
+
+  it('passes BigInt class ids through to class methods', async () => {
+    let receivedId: bigint | null = null;
+    server.stub('SpaceCenter', 'CelestialBody.GetName', (args) => {
+      const argBytes = args[0] ?? new Uint8Array();
+      let v = 0n;
+      let shift = 0n;
+      for (const b of argBytes) {
+        v |= BigInt(b & 0x7f) << shift;
+        if ((b & 0x80) === 0) break;
+        shift += 7n;
+      }
+      receivedId = v;
+      return encodeString('Mun');
+    });
+    await services.invoke<string>('SpaceCenter', 'CelestialBody.GetName', 99n);
+    expect(receivedId).toBe(99n);
+  });
+});

packages/krpc-client/tests/services.test.ts

@@ -0,0 +1,263 @@
+import { describe, it, expect } from 'vitest';
+import { ServiceCache, type RawServicesMessage } from '../src/services.js';
+
+/**
+ * A small hand-crafted services message that mirrors the shape we'd
+ * get from KRPC.GetServices() on a real KSP install. Just enough
+ * services/procedures/enums to exercise the cache.
+ */
+const SAMPLE_RAW: RawServicesMessage = {
+  services: [
+    {
+      name: 'SpaceCenter',
+      procedures: [
+        {
+          name: 'GetUT',
+          parameters: [],
+          returnType: { code: 1, service: '', name: '', types: [] }, // DOUBLE
+          returnIsNullable: false,
+        },
+        {
+          name: 'GetBodies',
+          parameters: [],
+          returnType: {
+            code: 301, // LIST
+            service: '',
+            name: '',
+            types: [{ code: 100, service: 'SpaceCenter', name: 'CelestialBody', types: [] }],
+          },
+          returnIsNullable: false,
+        },
+        {
+          name: 'CelestialBody.GetName',
+          parameters: [
+            {
+              name: 'self',
+              type: { code: 100, service: 'SpaceCenter', name: 'CelestialBody', types: [] },
+              nullable: false,
+            },
+          ],
+          returnType: { code: 8, service: '', name: '', types: [] }, // STRING
+          returnIsNullable: false,
+        },
+        {
+          name: 'CelestialBody.GetParent',
+          parameters: [
+            {
+              name: 'self',
+              type: { code: 100, service: 'SpaceCenter', name: 'CelestialBody', types: [] },
+              nullable: false,
+            },
+          ],
+          // Nullable CelestialBody (i.e. Sun has no parent).
+          returnType: { code: 100, service: 'SpaceCenter', name: 'CelestialBody', types: [] },
+          returnIsNullable: true,
+        },
+      ],
+      classes: [
+        { name: 'CelestialBody' },
+        { name: 'Vessel' },
+        { name: 'Orbit' },
+      ],
+      enumerations: [
+        {
+          name: 'VesselType',
+          values: [
+            { name: 'Ship', value: 0 },
+            { name: 'Station', value: 1 },
+            { name: 'Probe', value: 3 },
+            { name: 'Debris', value: 8 },
+          ],
+        },
+        {
+          name: 'VesselSituation',
+          values: [
+            { name: 'PreLaunch', value: 0 },
+            { name: 'Orbiting', value: 1 },
+            { name: 'Escaping', value: 2 },
+            { name: 'Landed', value: 4 },
+            { name: 'Splashed', value: 5 },
+          ],
+        },
+      ],
+    },
+    {
+      name: 'KRPC',
+      procedures: [
+        {
+          name: 'GetStatus',
+          parameters: [],
+          returnType: { code: 203, service: '', name: '', types: [] }, // STATUS
+          returnIsNullable: false,
+        },
+      ],
+      classes: [],
+      enumerations: [],
+    },
+  ],
+};
+
+describe('ServiceCache', () => {
+  it('builds from a raw services message', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    expect(cache.procedureCount()).toBe(5);
+    expect(cache.serviceNames()).toEqual(['KRPC', 'SpaceCenter']);
+  });
+
+  it('looks up a top-level procedure', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    const r = cache.lookup('SpaceCenter', 'GetUT');
+    expect(r.found).toBe(true);
+    if (!r.found) throw new Error('unreachable');
+    expect(r.info.service).toBe('SpaceCenter');
+    expect(r.info.name).toBe('GetUT');
+    expect(r.info.returnType.code).toBe(1); // DOUBLE
+    expect(r.info.returnIsNullable).toBe(false);
+    expect(r.info.parameters).toHaveLength(0);
+  });
+
+  it('looks up a class-prefixed procedure', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    const r = cache.lookup('SpaceCenter', 'CelestialBody.GetName');
+    expect(r.found).toBe(true);
+    if (!r.found) throw new Error('unreachable');
+    expect(r.info.parameters).toHaveLength(1);
+    expect(r.info.parameters[0]?.name).toBe('self');
+    expect(r.info.parameters[0]?.type.code).toBe(100); // CLASS
+    expect(r.info.parameters[0]?.type.name).toBe('CelestialBody');
+    expect(r.info.returnType.code).toBe(8); // STRING
+  });
+
+  it('returns not-found for an unknown procedure', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    expect(cache.lookup('SpaceCenter', 'GetNothing').found).toBe(false);
+    expect(cache.lookup('Nope', 'X').found).toBe(false);
+  });
+
+  it('returns not-found for an unknown service', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    expect(cache.lookup('KerbalAlarmClock', 'GetAlarms').found).toBe(false);
+  });
+
+  it('records returnIsNullable for nullable CLASS returns', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    const r = cache.lookup('SpaceCenter', 'CelestialBody.GetParent');
+    expect(r.found).toBe(true);
+    if (!r.found) throw new Error('unreachable');
+    expect(r.info.returnIsNullable).toBe(true);
+    expect(r.info.returnType.code).toBe(100);
+    expect(r.info.returnType.name).toBe('CelestialBody');
+  });
+
+  it('resolves enum values by name', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    expect(cache.getEnumValue('SpaceCenter', 'VesselType', 'Ship')).toBe(0);
+    expect(cache.getEnumValue('SpaceCenter', 'VesselType', 'Station')).toBe(1);
+    expect(cache.getEnumValue('SpaceCenter', 'VesselType', 'Probe')).toBe(3);
+    expect(cache.getEnumValue('SpaceCenter', 'VesselSituation', 'Orbiting')).toBe(1);
+  });
+
+  it('throws for unknown enum or enum value', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    expect(() => cache.getEnumValue('SpaceCenter', 'NoSuch', 'X')).toThrow(/unknown enum/);
+    expect(() => cache.getEnumValue('SpaceCenter', 'VesselType', 'Hovercraft')).toThrow(
+      /unknown value/,
+    );
+  });
+
+  it('resolves enum value names by code', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    expect(cache.getEnumName('SpaceCenter', 'VesselType', 0)).toBe('Ship');
+    expect(cache.getEnumName('SpaceCenter', 'VesselType', 3)).toBe('Probe');
+    expect(cache.getEnumName('SpaceCenter', 'VesselType', 999)).toBeNull();
+  });
+
+  it('lists enum value names', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    const names = cache.getEnumNames('SpaceCenter', 'VesselType');
+    expect(names).toEqual(['Debris', 'Probe', 'Ship', 'Station']); // sorted
+  });
+
+  it('lists procedures in a service', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    const procs = cache.proceduresInService('SpaceCenter');
+    expect(procs).toContain('SpaceCenter.GetUT');
+    expect(procs).toContain('SpaceCenter.CelestialBody.GetName');
+    expect(procs).toContain('SpaceCenter.CelestialBody.GetParent');
+  });
+
+  it('preserves nested list type info', () => {
+    const cache = new ServiceCache(SAMPLE_RAW);
+    const r = cache.lookup('SpaceCenter', 'GetBodies');
+    expect(r.found).toBe(true);
+    if (!r.found) throw new Error('unreachable');
+    expect(r.info.returnType.code).toBe(301); // LIST
+    expect(r.info.returnType.types).toHaveLength(1);
+    expect(r.info.returnType.types[0]?.code).toBe(100);
+    expect(r.info.returnType.types[0]?.name).toBe('CelestialBody');
+  });
+
+  it('handles procedures with no return type (returnType is null)', () => {
+    // Real kRPC server omits the `return_type` field for void
+    // procedures (e.g. AddStream, setters). protobufjs decodes
+    // missing message fields as null. Our cache must not crash.
+    const raw = {
+      services: [
+        {
+          name: 'KRPC',
+          procedures: [
+            {
+              name: 'AddStream',
+              parameters: [],
+              returnType: null, // <-- the trigger
+              returnIsNullable: false,
+            },
+          ],
+          classes: [],
+          enumerations: [],
+        },
+      ],
+    };
+    const cache = new ServiceCache(raw as unknown as Parameters<typeof ServiceCache>[0]);
+    const r = cache.lookup('KRPC', 'AddStream');
+    expect(r.found).toBe(true);
+    if (!r.found) throw new Error('unreachable');
+    // Missing return type becomes NONE (code 0).
+    expect(r.info.returnType.code).toBe(0);
+  });
+
+  it('falls back to .NET-style getter/setter naming for C# properties', () => {
+    // The kRPC server exposes C# properties using .NET accessor
+    // conventions: a property `UT` on SpaceCenter becomes two
+    // procedures named `get_UT` and `set_UT`. User code typically
+    // writes `SpaceCenter.GetUT()` (PascalCase). The cache must
+    // transparently translate to the wire-format name.
+    const raw = {
+      services: [
+        {
+          name: 'SpaceCenter',
+          procedures: [
+            { name: 'get_UT', parameters: [], returnType: null, returnIsNullable: false },
+            { name: 'set_UT', parameters: [], returnType: null, returnIsNullable: false },
+            { name: 'get_ActiveVessel', parameters: [], returnType: null, returnIsNullable: true },
+            { name: 'CelestialBody.get_Name', parameters: [], returnType: null, returnIsNullable: false },
+          ],
+          classes: [],
+          enumerations: [],
+        },
+      ],
+    };
+    const cache = new ServiceCache(raw as unknown as Parameters<typeof ServiceCache>[0]);
+    // Top-level PascalCase -> .NET getter
+    expect(cache.lookup('SpaceCenter', 'GetUT').found).toBe(true);
+    // Top-level PascalCase -> .NET setter
+    expect(cache.lookup('SpaceCenter', 'SetUT').found).toBe(true);
+    expect(cache.lookup('SpaceCenter', 'GetActiveVessel').found).toBe(true);
+    // Class-prefixed: "CelestialBody.GetName" -> "CelestialBody.get_Name"
+    expect(cache.lookup('SpaceCenter', 'CelestialBody.GetName').found).toBe(true);
+    // Exact match still works
+    expect(cache.lookup('SpaceCenter', 'get_UT').found).toBe(true);
+    // And unknown names still return not-found
+    expect(cache.lookup('SpaceCenter', 'NoSuchProcedure').found).toBe(false);
+  });
+});

packages/krpc-client/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "./dist",
+    "rootDir": "./src",
+    "types": ["node"]
+  },
+  "include": ["src/**/*"]
+}

packages/krpc-client/vitest.config.ts

@@ -0,0 +1,8 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    include: ['tests/**/*.test.ts'],
+    environment: 'node',
+  },
+});

pnpm-lock.yaml

@@ -143,6 +143,28 @@ importers:
         specifier: ^2.1.1
         version: 2.1.9(@types/node@22.19.19)
 
+  apps/tools/ksp-bridge:
+    dependencies:
+      '@kerbal-rt/krpc-client':
+        specifier: workspace:*
+        version: link:../../../packages/krpc-client
+      '@kerbal-rt/shared-types':
+        specifier: workspace:*
+        version: link:../../../packages/shared-types
+    devDependencies:
+      '@types/node':
+        specifier: ^22.5.0
+        version: 22.19.19
+      tsx:
+        specifier: ^4.19.1
+        version: 4.22.4
+      typescript:
+        specifier: ^5.6.2
+        version: 5.9.3
+      vitest:
+        specifier: ^2.1.1
+        version: 2.1.9(@types/node@22.19.19)
+
   apps/tools/mock-telemetry:
     dependencies:
       '@kerbal-rt/orbital-math':
@@ -181,6 +203,22 @@ importers:
         specifier: ^2.1.1
         version: 2.1.9(@types/node@22.19.19)
 
+  packages/krpc-client:
+    dependencies:
+      protobufjs:
+        specifier: ^7.4.0
+        version: 7.6.2
+    devDependencies:
+      '@types/node':
+        specifier: ^22.5.0
+        version: 22.19.19
+      typescript:
+        specifier: ^5.6.2
+        version: 5.9.3
+      vitest:
+        specifier: ^2.1.1
+        version: 2.1.9(@types/node@22.19.19)
+
   packages/orbital-math:
     dependencies:
       '@kerbal-rt/shared-types':
@@ -1084,6 +1122,66 @@ packages:
       }
     engines: { node: '>=14' }
 
+  '@protobufjs/aspromise@1.1.2':
+    resolution:
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+        integrity: sha512-j+gKExEuLmKwvz3OgROXtrJ2UG2x8Ch2YZUxahh+s1F2HZ+wAceUNLkvy6zKCPVRkU++ZWQrdxsUeQXmcg4uoQ==,
+      }
+
+  '@protobufjs/base64@1.1.2':
+    resolution:
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+      }
+
+  '@protobufjs/codegen@2.0.5':
+    resolution:
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+      }
+
+  '@protobufjs/eventemitter@1.1.1':
+    resolution:
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+      }
+
+  '@protobufjs/fetch@1.1.1':
+    resolution:
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+      }
+
+  '@protobufjs/float@1.0.2':
+    resolution:
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+      }
+
+  '@protobufjs/inquire@1.1.2':
+    resolution:
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+      }
+
+  '@protobufjs/path@1.1.2':
+    resolution:
+      {
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+      }
+
+  '@protobufjs/pool@1.1.0':
+    resolution:
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+      }
+
+  '@protobufjs/utf8@1.1.1':
+    resolution:
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+      }
+
   '@rolldown/pluginutils@1.0.0-beta.27':
     resolution:
       {
@@ -3110,6 +3208,12 @@ packages:
         integrity: sha512-0KpjqXRVvrYyCsX1swR/XTK0va6VQkQM6MNo7PqW77ByjAhoARA8EfrP1N4+KlKj8YS0ZUCtRT/YUuhyYDujIQ==,
       }
 
+  long@5.3.2:
+    resolution:
+      {
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+      }
+
   loose-envify@1.4.0:
     resolution:
       {
@@ -3456,6 +3560,13 @@ packages:
         integrity: sha512-oj87CgZICdulUohogVAR7AjlC0327U4el4L6eAvOqCeudMDVU0NThNaV+b9Df4dXgSP1gXMTnPdhfe/2qDH5cg==,
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+  protobufjs@7.6.2:
+    resolution:
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+      }
+    engines: { node: '>=12.0.0' }
+
   punycode@2.3.1:
     resolution:
       {
@@ -4607,6 +4718,28 @@ snapshots:
   '@pkgjs/parseargs@0.11.0':
     optional: true
 
+  '@protobufjs/aspromise@1.1.2': {}
+
+  '@protobufjs/base64@1.1.2': {}
+
+  '@protobufjs/codegen@2.0.5': {}
+
+  '@protobufjs/eventemitter@1.1.1': {}
+
+  '@protobufjs/fetch@1.1.1':
+    dependencies:
+      '@protobufjs/aspromise': 1.1.2
+
+  '@protobufjs/float@1.0.2': {}
+
+  '@protobufjs/inquire@1.1.2': {}
+
+  '@protobufjs/path@1.1.2': {}
+
+  '@protobufjs/pool@1.1.0': {}
+
+  '@protobufjs/utf8@1.1.1': {}
+
   '@rolldown/pluginutils@1.0.0-beta.27': {}
 
   '@rollup/rollup-android-arm-eabi@4.61.0':
@@ -5978,6 +6111,8 @@ snapshots:
 
   lodash.merge@4.6.2: {}
 
+  long@5.3.2: {}
+
   loose-envify@1.4.0:
     dependencies:
       js-tokens: 4.0.0
@@ -6176,6 +6311,21 @@ snapshots:
       object-assign: 4.1.1
       react-is: 16.13.1
 
+  protobufjs@7.6.2:
+    dependencies:
+      '@protobufjs/aspromise': 1.1.2
+      '@protobufjs/base64': 1.1.2
+      '@protobufjs/codegen': 2.0.5
+      '@protobufjs/eventemitter': 1.1.1
+      '@protobufjs/fetch': 1.1.1
+      '@protobufjs/float': 1.0.2
+      '@protobufjs/inquire': 1.1.2
+      '@protobufjs/path': 1.1.2
+      '@protobufjs/pool': 1.1.0
+      '@protobufjs/utf8': 1.1.1
+      '@types/node': 22.19.19
+      long: 5.3.2
+
   punycode@2.3.1: {}
 
   queue-microtask@1.2.3: {}