feat: show transcript file size in session status

Add transcript size monitoring to /status and session_status tool.
Displays file size and message count (e.g. '📄 Transcript: 1.2 MB,
627 messages'). Shows ⚠️ warning when transcript exceeds 1 MB, which
helps catch sessions approaching the compaction death spiral described
in #13624.

- getTranscriptInfo() reads JSONL file stat + line count
- Wired into both /status command and session_status tool
- 8 new tests covering file reading, formatting, and edge cases

src/auto-reply/status.ts

@@ -55,6 +55,15 @@ type QueueStatus = {
   showDetails?: boolean;
 };
 
+export type TranscriptInfo = {
+  /** File size in bytes. */
+  sizeBytes: number;
+  /** Number of non-empty lines (messages) in the transcript. */
+  messageCount: number;
+  /** Absolute path to the transcript file. */
+  filePath: string;
+};
+
 type StatusArgs = {
   config?: OpenClawConfig;
   agent: AgentConfig;
@@ -75,6 +84,7 @@ type StatusArgs = {
   mediaDecisions?: MediaUnderstandingDecision[];
   subagentsLine?: string;
   includeTranscriptUsage?: boolean;
+  transcriptInfo?: TranscriptInfo;
   now?: number;
 };
 
@@ -324,6 +334,74 @@ const formatVoiceModeLine = (
   return `🔊 Voice: ${autoMode} · provider=${provider} · limit=${maxLength} · summary=${summarize}`;
 };
 
+/**
+ * Read transcript file metadata (size + line count) for a session.
+ * Returns `undefined` when the file does not exist or cannot be read.
+ */
+export function getTranscriptInfo(params: {
+  sessionId?: string;
+  sessionEntry?: SessionEntry;
+  agentId?: string;
+  sessionKey?: string;
+  storePath?: string;
+}): TranscriptInfo | undefined {
+  if (!params.sessionId) {
+    return undefined;
+  }
+  let logPath: string;
+  try {
+    const resolvedAgentId =
+      params.agentId ??
+      (params.sessionKey ? resolveAgentIdFromSessionKey(params.sessionKey) : undefined);
+    logPath = resolveSessionFilePath(
+      params.sessionId,
+      params.sessionEntry,
+      resolveSessionFilePathOptions({ agentId: resolvedAgentId, storePath: params.storePath }),
+    );
+  } catch {
+    return undefined;
+  }
+  try {
+    const stat = fs.statSync(logPath);
+    if (!stat.isFile()) {
+      return undefined;
+    }
+    // Count non-empty lines for message count.
+    const content = fs.readFileSync(logPath, "utf-8");
+    let messageCount = 0;
+    for (const line of content.split("\n")) {
+      if (line.trim()) {
+        messageCount += 1;
+      }
+    }
+    return { sizeBytes: stat.size, messageCount, filePath: logPath };
+  } catch {
+    return undefined;
+  }
+}
+
+function formatFileSize(bytes: number): string {
+  if (bytes < 1024) {
+    return `${bytes} B`;
+  }
+  if (bytes < 1024 * 1024) {
+    return `${(bytes / 1024).toFixed(1)} KB`;
+  }
+  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
+}
+
+/** Size threshold (bytes) above which a warning emoji is shown. Default: 1 MB. */
+const TRANSCRIPT_SIZE_WARNING_BYTES = 1024 * 1024;
+
+function formatTranscriptLine(info: TranscriptInfo | undefined): string | null {
+  if (!info) {
+    return null;
+  }
+  const sizeLabel = formatFileSize(info.sizeBytes);
+  const warning = info.sizeBytes >= TRANSCRIPT_SIZE_WARNING_BYTES ? " ⚠️" : "";
+  return `📄 Transcript: ${sizeLabel}, ${info.messageCount} message${info.messageCount === 1 ? "" : "s"}${warning}`;
+}
+
 export function buildStatusMessage(args: StatusArgs): string {
   const now = args.now ?? Date.now();
   const entry = args.sessionEntry;
@@ -472,6 +550,7 @@ export function buildStatusMessage(args: StatusArgs): string {
     usagePair && costLine ? `${usagePair} · ${costLine}` : (usagePair ?? costLine);
   const mediaLine = formatMediaUnderstandingLine(args.mediaDecisions);
   const voiceLine = formatVoiceModeLine(args.config, args.sessionEntry);
+  const transcriptLine = formatTranscriptLine(args.transcriptInfo);
 
   return [
     versionLine,
@@ -479,6 +558,7 @@ export function buildStatusMessage(args: StatusArgs): string {
     modelLine,
     usageCostLine,
     `📚 ${contextLine}`,
+    transcriptLine,
     mediaLine,
     args.usageLine,
     `🧵 ${sessionLine}`,