fix: release stale session locks and add watchdog for hung API calls (#18060)

When a model API call hangs indefinitely (e.g. Anthropic quota exceeded
mid-call), the gateway acquires a session .jsonl.lock but the promise
never resolves, so the try/finally block never reaches release(). Since
the owning PID is the gateway itself, stale detection cannot help —
isPidAlive() always returns true.

This commit adds four layers of defense:

1. **In-process lock watchdog** (session-write-lock.ts)
   - Track acquiredAt timestamp on each held lock
   - 60-second interval timer checks all held locks
   - Auto-releases any lock held longer than maxHoldMs (default 5 min)
   - Catches the hung-API-call case that try/finally cannot

2. **Gateway startup cleanup** (server-startup.ts)
   - On boot, scan all agent session directories for *.jsonl.lock files
   - Remove locks with dead PIDs or older than staleMs (30 min)
   - Log each cleaned lock for diagnostics

3. **openclaw doctor stale lock detection** (doctor-session-locks.ts)
   - New health check scans for .jsonl.lock files
   - Reports PID status and age of each lock found
   - In --fix mode, removes stale locks automatically

4. **Transcript error entry on API failure** (attempt.ts)
   - When promptError is set, write an error marker to the session
     transcript before releasing the lock
   - Preserves conversation history even on model API failures

Closes #18060

src/agents/pi-embedded-runner/run/attempt.ts

@@ -848,6 +848,7 @@ export async function runEmbeddedAttempt(
             }).sessionAgentId;
 
       let promptError: unknown = null;
+      let promptErrorSource: "prompt" | "compaction" | null = null;
       try {
         const promptStartedAt = Date.now();
 
@@ -1000,6 +1001,7 @@ export async function runEmbeddedAttempt(
           }
         } catch (err) {
           promptError = err;
+          promptErrorSource = "prompt";
         } finally {
           log.debug(
             `embedded run prompt end: runId=${params.runId} sessionId=${params.sessionId} durationMs=${Date.now() - promptStartedAt}`,
@@ -1022,6 +1024,7 @@ export async function runEmbeddedAttempt(
           if (isRunnerAbortError(err)) {
             if (!promptError) {
               promptError = err;
+              promptErrorSource = "compaction";
             }
             if (!isProbeSession) {
               log.debug(
@@ -1070,6 +1073,23 @@ export async function runEmbeddedAttempt(
         }
         messagesSnapshot = snapshotSelection.messagesSnapshot;
         sessionIdUsed = snapshotSelection.sessionIdUsed;
+
+        if (promptError && promptErrorSource === "prompt") {
+          try {
+            sessionManager.appendCustomEntry("openclaw:prompt-error", {
+              timestamp: Date.now(),
+              runId: params.runId,
+              sessionId: params.sessionId,
+              provider: params.provider,
+              model: params.modelId,
+              api: params.model.api,
+              error: describeUnknownError(promptError),
+            });
+          } catch (entryErr) {
+            log.warn(`failed to persist prompt error entry: ${String(entryErr)}`);
+          }
+        }
+
         cacheTrace?.recordStage("session:after", {
           messages: messagesSnapshot,
           note: timedOutDuringCompaction