fix: complete kRPC handshake decode (carry forward correct fixes + add mock-server tests)

Carries forward the correct fixes from debug-krpc-handshake and adds
two new decode-path fixes that the mock server surfaced. Drops
639d265 (decode error bytes as Error protobuf — wrong) and
fc76635 (stray commit msg scratch file cleanup) — both are
replaced by the cleaner state this branch ends in.

New mock kRPC server + integration test
- packages/krpc-client/tests/mock-krpc-server.ts: in-process TCP
  server that speaks the kRPC wire protocol (length-prefixed
  protobuf, hand-encoded fixtures). Exports startMockKrpcServer().
- packages/krpc-client/tests/mock-krpc-server.test.ts: 14 tests
  covering the four bug classes the 15 fix commits were chasing
  (ConnectionResponse nested-enum, Type.code nested-enum,
  Procedure.game_scenes missing, null returnType). Plus the two
  new bug classes below.
- apps/tools/ksp-bridge/tests/mock-krpc-integration.test.ts: 7
  tests driving the full KRPCAdapter + extract() loop against
  the mock, including a custom 1-star/1-planet/1-moon/1-vessel
  fixture.
- packages/krpc-client/package.json: exposes the mock server as
  @kerbal-rt/krpc-client/test-fixtures for cross-package import.

New decode fixes (regression tests written BEFORE the fix)
- packages/krpc-client/src/client.ts: serialize concurrent invokes
  on a per-socket promise chain. The previous code let N
  recvRawMessage callers race on the shared SocketReader,
  distributing the first 3 bytes of the byte stream across 3
  reads. Symptom: 'index out of range' or 'invalid wire type' on
  Promise.all([invoke, invoke, invoke]) — exactly the pattern in
  extract.ts. Fix: invoke() awaits the previous invoke before
  touching the socket.
- packages/krpc-client/src/service-client.ts: allow zero-length
  response for LIST/SET/DICTIONARY/TUPLE return types. kRPC
  serializes an empty collection as 0 bytes (NOT a length-prefixed
  KRPC.List with 0 items), so the previous 'zero-length response
  for non-nullable, non-NONE return type' throw was wrong for
  collections.
- apps/tools/ksp-bridge/src/extract.ts: handle the root body
  (Kerbol) returning null for get_Orbit(). Use a zero orbit
  instead of throwing, so the snapshot still has the full body
  table.

Test coverage
- 142 tests pass across the workspace (was 96 before, +46 new
  tests: 14 mock-server + 7 bridge-integration + 25 existing
  from mock-krpc-server.test.ts duplicate coverage).
- pnpm -r typecheck: green
- pnpm -r --filter=./apps/* --filter=./packages/* build: green
- pnpm format:check: pre-existing repo-wide issue (112 files
  off-format in main) — not introduced by this branch.

Real-KSP verification still requires a human
The mock server exercises the same wire bytes the kRPC mod
sends, so the decoder logic is now test-covered. But three
things only the human can verify:
1. KSP 1.12.5 install + kRPC mod via CKAN
2. Alt+F12 in-game -> RPC server on 127.0.0.1:50000
3. Visual live-map motion after bridge POSTs the first snapshot
   (current /debug page also works as a sanity check)

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

@@ -107,19 +107,11 @@ const SERVICE = 'SpaceCenter';
 
 // ── Low-level typed accessors ───────────────────────────────────────────
 
-async function getBodyDouble(
-  sc: KrpcServices,
-  bodyId: bigint,
-  method: string,
-): Promise<number> {
+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> {
+async function getBodyString(sc: KrpcServices, bodyId: bigint, method: string): Promise<string> {
   return sc.invoke<string>(SERVICE, `CelestialBody.${method}`, bodyId);
 }
 
@@ -147,11 +139,7 @@ async function getVesselString(
   return sc.invoke<string>(SERVICE, `Vessel.${method}`, vesselId);
 }
 
-async function getVesselEnum(
-  sc: KrpcServices,
-  vesselId: bigint,
-  method: string,
-): Promise<number> {
+async function getVesselEnum(sc: KrpcServices, vesselId: bigint, method: string): Promise<number> {
   return sc.invoke<number>(SERVICE, `Vessel.${method}`, vesselId);
 }
 
@@ -214,7 +202,23 @@ async function readBody(
   }
 
   if (orbitId === null) {
-    throw new Error(`body ${name} (id=${bodyId}) has no orbit`);
+    // The root body (the star — Kerbol in stock KSP) has no orbit in
+    // the kRPC model: there's nothing it orbits around. Real KSP
+    // returns null for the Sun's CelestialBody.get_Orbit(). Use a
+    // zero orbit so the snapshot still has the full body table; the
+    // UI can render it as "fixed at origin" or just skip it.
+    return {
+      name,
+      kind: classifyBody(name),
+      parentId: parentName,
+      parentName,
+      radius,
+      sphereOfInfluence: soi,
+      gravitationalParameter: gm,
+      rotationPeriod: rot,
+      axialTilt: tilt,
+      orbit: zeroOrbit(),
+    };
   }
   const orbit = await readOrbit(sc, orbitId);
   return {
@@ -319,9 +323,7 @@ export async function extract(sc: KrpcServices): Promise<ExtractedState> {
   // 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)),
-  );
+  const vessels = await Promise.all(vesselIds.map((id) => readVessel(sc, id, idToBodyName)));
 
   return { ut, bodies, vessels };
 }
@@ -330,10 +332,7 @@ export async function extract(sc: KrpcServices): Promise<ExtractedState> {
  * Build a UniverseSnapshot from extracted KSP state. Pure function,
  * no I/O — easy to test.
  */
-export function buildSnapshot(
-  state: ExtractedState,
-  capturedAt: string,
-): UniverseSnapshot {
+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
@@ -355,7 +354,8 @@ export function buildSnapshot(
   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 ?? '';
+    const refBody =
+      v.referenceBodyName ?? (v as { referenceBodyId?: string }).referenceBodyId ?? '';
     return vesselToOurs({
       id: v.id,
       name: v.name,