diff --git a/apps/tools/ksp-bridge/src/index.ts b/apps/tools/ksp-bridge/src/index.ts
index 557ff6f..86605c0 100644
--- a/apps/tools/ksp-bridge/src/index.ts
+++ b/apps/tools/ksp-bridge/src/index.ts
@@ -46,8 +46,10 @@ function err(msg: string): void {
   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`);
+  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.
@@ -60,8 +62,28 @@ async function main(): Promise<void> {
     await adapter.connect();
     log(`connected to kRPC at ${HOST}:${RPC_PORT} — running with real KSP state`);
   } catch (e) {
-    const msg = e === null ? 'null' : e instanceof Error ? e.message : String(e);
-    log(`no kRPC server at ${HOST}:${RPC_PORT}: ${msg}`);
+    // Hardened error formatter: handles null, undefined, Error,
+    // strings, and arbitrary objects. Never crashes the formatter
+    // itself, so we always see *something*.
+    let msg: string;
+    if (e === null) {
+      msg = 'null';
+    } else if (e === undefined) {
+      msg = 'undefined';
+    } else if (typeof e === 'string') {
+      msg = e;
+    } else if (e instanceof Error) {
+      msg = e.message;
+    } else if (typeof e === 'object') {
+      try {
+        msg = JSON.stringify(e);
+      } catch {
+        msg = String(e);
+      }
+    } else {
+      msg = String(e);
+    }
+    log(`[${BUILD_TAG}] no kRPC server at ${HOST}:${RPC_PORT}: ${msg}`);
     log('Falling back to MOCK mode (synthetic state).');
     return runMock();
   }
@@ -165,6 +187,14 @@ function mockState(ut: number): ExtractedState {
 }
 
 main().catch((e) => {
-  err(`fatal: ${e}`);
+  let msg: string;
+  if (e === null) msg = 'null';
+  else if (e === undefined) msg = 'undefined';
+  else if (e instanceof Error) msg = `${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);
 });