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/shared/worker-utils.ts

@@ -6,7 +6,21 @@ import { SettingsDefaultsManager } from "./SettingsDefaultsManager.js";
 import { MARKETPLACE_ROOT } from "./paths.js";
 
 // Named constants for health checks
-const HEALTH_CHECK_TIMEOUT_MS = getTimeout(HOOK_TIMEOUTS.HEALTH_CHECK);
+// Allow env var override for users on slow systems (e.g., CLAUDE_MEM_HEALTH_TIMEOUT_MS=10000)
+const HEALTH_CHECK_TIMEOUT_MS = (() => {
+  const envVal = process.env.CLAUDE_MEM_HEALTH_TIMEOUT_MS;
+  if (envVal) {
+    const parsed = parseInt(envVal, 10);
+    if (Number.isFinite(parsed) && parsed >= 500 && parsed <= 300000) {
+      return parsed;
+    }
+    // Invalid env var — log once and use default
+    logger.warn('SYSTEM', 'Invalid CLAUDE_MEM_HEALTH_TIMEOUT_MS, using default', {
+      value: envVal, min: 500, max: 300000
+    });
+  }
+  return getTimeout(HOOK_TIMEOUTS.HEALTH_CHECK);
+})();
 
 /**
  * Fetch with a timeout using Promise.race instead of AbortSignal.
@@ -89,12 +103,22 @@ async function isWorkerHealthy(): Promise<boolean> {
 }
 
 /**
- * Get the current plugin version from package.json
+ * Get the current plugin version from package.json.
+ * Returns 'unknown' on ENOENT/EBUSY (shutdown race condition, fix #1042).
  */
 function getPluginVersion(): string {
-  const packageJsonPath = path.join(MARKETPLACE_ROOT, 'package.json');
-  const packageJson = JSON.parse(readFileSync(packageJsonPath, 'utf-8'));
-  return packageJson.version;
+  try {
+    const packageJsonPath = path.join(MARKETPLACE_ROOT, 'package.json');
+    const packageJson = JSON.parse(readFileSync(packageJsonPath, 'utf-8'));
+    return packageJson.version;
+  } catch (error: unknown) {
+    const code = (error as NodeJS.ErrnoException).code;
+    if (code === 'ENOENT' || code === 'EBUSY') {
+      logger.debug('SYSTEM', 'Could not read plugin version (shutdown race)', { code });
+      return 'unknown';
+    }
+    throw error;
+  }
 }
 
 /**
@@ -115,18 +139,33 @@ async function getWorkerVersion(): Promise<string> {
 /**
  * Check if worker version matches plugin version
  * Note: Auto-restart on version mismatch is now handled in worker-service.ts start command (issue #484)
- * This function logs for informational purposes only
+ * This function logs for informational purposes only.
+ * Skips comparison when either version is 'unknown' (fix #1042 — avoids restart loops).
  */
 async function checkWorkerVersion(): Promise<void> {
-  const pluginVersion = getPluginVersion();
-  const workerVersion = await getWorkerVersion();
+  try {
+    const pluginVersion = getPluginVersion();
 
-  if (pluginVersion !== workerVersion) {
-    // Just log debug info - auto-restart handles the mismatch in worker-service.ts
-    logger.debug('SYSTEM', 'Version check', {
-      pluginVersion,
-      workerVersion,
-      note: 'Mismatch will be auto-restarted by worker-service start command'
+    // Skip version check if plugin version couldn't be read (shutdown race)
+    if (pluginVersion === 'unknown') return;
+
+    const workerVersion = await getWorkerVersion();
+
+    // Skip version check if worker version is 'unknown' (avoids restart loops)
+    if (workerVersion === 'unknown') return;
+
+    if (pluginVersion !== workerVersion) {
+      // Just log debug info - auto-restart handles the mismatch in worker-service.ts
+      logger.debug('SYSTEM', 'Version check', {
+        pluginVersion,
+        workerVersion,
+        note: 'Mismatch will be auto-restarted by worker-service start command'
+      });
+    }
+  } catch (error) {
+    // Version check is informational — don't fail the hook
+    logger.debug('SYSTEM', 'Version check failed', {
+      error: error instanceof Error ? error.message : String(error)
     });
   }
 }