fix: hook resilience and worker lifecycle improvements (#957, #923, #984, #987, #1042)

Reduce timeouts to eliminate 10-30s startup delay when worker is dead
(common on WSL2 after hibernate). Add stale PID detection, graceful
error handling across all handlers, and error classification that
distinguishes worker unavailability from handler bugs.

- HEALTH_CHECK 30s→3s, new POST_SPAWN_WAIT (5s), PORT_IN_USE_WAIT (3s)
- isProcessAlive() with EPERM handling, cleanStalePidFile()
- getPluginVersion() try-catch for shutdown race (#1042)
- isWorkerUnavailableError: transport+5xx+429→exit 0, 4xx→exit 2
- No-op handler for unknown event types (#984)
- Wrap all handler fetch calls in try-catch for graceful degradation
- CLAUDE_MEM_HEALTH_TIMEOUT_MS env var override with validation

src/cli/handlers/observation.ts

@@ -48,25 +48,33 @@ export const observationHandler: EventHandler = {
     }
 
     // Send to worker - worker handles privacy check and database operations
-    const response = await fetch(`http://127.0.0.1:${port}/api/sessions/observations`, {
-      method: 'POST',
-      headers: { 'Content-Type': 'application/json' },
-      body: JSON.stringify({
-        contentSessionId: sessionId,
-        tool_name: toolName,
-        tool_input: toolInput,
-        tool_response: toolResponse,
-        cwd
-      })
-      // Note: Removed signal to avoid Windows Bun cleanup issue (libuv assertion)
-    });
+    try {
+      const response = await fetch(`http://127.0.0.1:${port}/api/sessions/observations`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          contentSessionId: sessionId,
+          tool_name: toolName,
+          tool_input: toolInput,
+          tool_response: toolResponse,
+          cwd
+        })
+        // Note: Removed signal to avoid Windows Bun cleanup issue (libuv assertion)
+      });
 
-    if (!response.ok) {
-      throw new Error(`Observation storage failed: ${response.status}`);
+      if (!response.ok) {
+        // Log but don't throw — observation storage failure should not block tool use
+        logger.warn('HOOK', 'Observation storage failed, skipping', { status: response.status, toolName });
+        return { continue: true, suppressOutput: true, exitCode: HOOK_EXIT_CODES.SUCCESS };
+      }
+
+      logger.debug('HOOK', 'Observation sent successfully', { toolName });
+    } catch (error) {
+      // Worker unreachable — skip observation gracefully
+      logger.warn('HOOK', 'Observation fetch error, skipping', { error: error instanceof Error ? error.message : String(error) });
+      return { continue: true, suppressOutput: true, exitCode: HOOK_EXIT_CODES.SUCCESS };
     }
 
-    logger.debug('HOOK', 'Observation sent successfully', { toolName });
-
     return { continue: true, suppressOutput: true };
   }
 };