fix(gateway): bound async session list transcript reads

Keep async sessions.list title/preview hydration on bounded transcript head/tail reads instead of full transcript index builds.

Validation:
- pnpm test:serial src/gateway/session-utils.fs.test.ts
- pnpm test:serial src/gateway/server.sessions.list-changed.test.ts
- pnpm exec oxfmt --check --threads=1 src/gateway/session-utils.fs.ts src/gateway/session-utils.fs.test.ts CHANGELOG.md
- OPENCLAW_TESTBOX=1 pnpm check:changed on tbx_01kqnw1j8japk3d8z24s6cv141

CHANGELOG.md

@@ -13,6 +13,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Gateway/sessions: keep async `sessions.list` title and preview hydration bounded to transcript head/tail reads so Control UI polling cannot full-scan large session transcripts every refresh. Thanks @vincentkoc.
 - Gateway: preserve stack diagnostics when `chat.send` or agent attachment parsing/staging fails, improving image-send failure triage. Refs #63432. (#75135) Thanks @keen0206.
 - Maintainer workflow: push prepared PR heads through GitHub's verified commit API by default and require an explicit override before git-protocol pushes can publish unsigned commits. Thanks @BunsDev.
 - Feishu: resolve setup/status probes through the selected/default account so multi-account configs with account-scoped app credentials show as configured and probeable. Fixes #72930. Thanks @brokemac79.

src/gateway/session-utils.fs.test.ts

@@ -24,6 +24,7 @@ import {
   readSessionMessagesAsync,
   readSessionMessages,
   readSessionTitleFieldsFromTranscript,
+  readSessionTitleFieldsFromTranscriptAsync,
   readSessionPreviewItemsFromTranscript,
   resolveSessionTranscriptCandidates,
 } from "./session-utils.fs.js";
@@ -471,6 +472,23 @@ describe("readSessionTitleFieldsFromTranscript cache", () => {
     expect(readSpy.mock.calls.length).toBeGreaterThan(readsAfterFirst);
     readSpy.mockRestore();
   });
+
+  test("keeps async title extraction bounded like the sync path", async () => {
+    const sessionId = "test-cache-async-bounded";
+    writeTranscript(tmpDir, sessionId, [
+      { type: "session", version: 1, id: sessionId },
+      ...Array.from({ length: 30 }, (_, index) => ({
+        message: { role: "assistant", content: `filler ${index} ${"x".repeat(512)}` },
+      })),
+      { message: { role: "user", content: "late title should not require a full scan" } },
+      { message: { role: "assistant", content: "tail preview" } },
+    ]);
+
+    await expect(readSessionTitleFieldsFromTranscriptAsync(sessionId, storePath)).resolves.toEqual({
+      firstUserMessage: null,
+      lastMessagePreview: "tail preview",
+    });
+  });
 });
 
 describe("readSessionMessages", () => {

src/gateway/session-utils.fs.ts

@@ -42,6 +42,7 @@ const transcriptMessageCountCache = new Map<
 >();
 const MAX_TRANSCRIPT_MESSAGE_COUNT_CACHE_ENTRIES = 5000;
 const TRANSCRIPT_ASYNC_READ_CHUNK_BYTES = 64 * 1024;
+type TranscriptFileHandle = Awaited<ReturnType<typeof fs.promises.open>>;
 
 function readSessionTitleFieldsCacheKey(
   filePath: string,
@@ -813,43 +814,47 @@ export async function readSessionTitleFieldsFromTranscriptAsync(
   if (cached) {
     return cached;
   }
-  const index = await readSessionTranscriptIndex(filePath);
-  if (!index) {
+
+  if (stat.size === 0) {
+    const empty = { firstUserMessage: null, lastMessagePreview: null };
+    setCachedSessionTitleFields(cacheKey, stat, empty);
+    return empty;
+  }
+
+  let handle: TranscriptFileHandle | null = null;
+  try {
+    handle = await fs.promises.open(filePath, "r");
+
+    let firstUserMessage: string | null = null;
+    try {
+      const chunk = await readTranscriptHeadChunkAsync(handle);
+      if (chunk) {
+        firstUserMessage = extractFirstUserMessageFromTranscriptChunk(chunk, opts);
+      }
+    } catch {
+      // ignore head read errors
+    }
+
+    let lastMessagePreview: string | null = null;
+    try {
+      lastMessagePreview = await readLastMessagePreviewFromOpenTranscriptAsync({
+        handle,
+        size: stat.size,
+      });
+    } catch {
+      // ignore tail read errors
+    }
+
+    const result = { firstUserMessage, lastMessagePreview };
+    setCachedSessionTitleFields(cacheKey, stat, result);
+    return result;
+  } catch {
     return { firstUserMessage: null, lastMessagePreview: null };
-  }
-
-  let firstUserMessage: string | null = null;
-  for (const entry of index.entries) {
-    const msg = entry.record.message as TranscriptMessage | undefined;
-    if (msg?.role !== "user") {
-      continue;
-    }
-    if (opts?.includeInterSession !== true && hasInterSessionUserProvenance(msg)) {
-      continue;
-    }
-    const text = extractTextFromContent(msg.content);
-    if (text) {
-      firstUserMessage = text;
-      break;
+  } finally {
+    if (handle) {
+      await handle.close().catch(() => undefined);
     }
   }
-
-  let lastMessagePreview: string | null = null;
-  for (const entry of index.entries.toReversed()) {
-    const msg = entry.record.message as TranscriptMessage | undefined;
-    if (!msg || (msg.role !== "user" && msg.role !== "assistant")) {
-      continue;
-    }
-    const text = extractTextFromContent(msg.content);
-    if (text) {
-      lastMessagePreview = text;
-      break;
-    }
-  }
-
-  const result = { firstUserMessage, lastMessagePreview };
-  setCachedSessionTitleFields(cacheKey, stat, result);
-  return result;
 }
 
 function extractTextFromContent(content: TranscriptMessage["content"]): string | null {
@@ -883,6 +888,18 @@ function readTranscriptHeadChunk(fd: number, maxBytes = 8192): string | null {
   return buf.toString("utf-8", 0, bytesRead);
 }
 
+async function readTranscriptHeadChunkAsync(
+  handle: TranscriptFileHandle,
+  maxBytes = 8192,
+): Promise<string | null> {
+  const buffer = Buffer.alloc(maxBytes);
+  const { bytesRead } = await handle.read(buffer, 0, buffer.length, 0);
+  if (bytesRead <= 0) {
+    return null;
+  }
+  return buffer.toString("utf-8", 0, bytesRead);
+}
+
 function extractFirstUserMessageFromTranscriptChunk(
   chunk: string,
   opts?: { includeInterSession?: boolean },
@@ -993,6 +1010,41 @@ function readLastMessagePreviewFromOpenTranscript(params: {
   return null;
 }
 
+async function readLastMessagePreviewFromOpenTranscriptAsync(params: {
+  handle: TranscriptFileHandle;
+  size: number;
+}): Promise<string | null> {
+  const readStart = Math.max(0, params.size - LAST_MSG_MAX_BYTES);
+  const readLen = Math.min(params.size, LAST_MSG_MAX_BYTES);
+  const buffer = Buffer.alloc(readLen);
+  const { bytesRead } = await params.handle.read(buffer, 0, readLen, readStart);
+  if (bytesRead <= 0) {
+    return null;
+  }
+
+  const chunk = buffer.toString("utf-8", 0, bytesRead);
+  const lines = chunk.split(/\r?\n/).filter((line) => line.trim());
+  const tailLines = lines.slice(-LAST_MSG_MAX_LINES);
+
+  for (let i = tailLines.length - 1; i >= 0; i--) {
+    const line = tailLines[i];
+    try {
+      const parsed = JSON.parse(line);
+      const msg = parsed?.message as TranscriptMessage | undefined;
+      if (msg?.role !== "user" && msg?.role !== "assistant") {
+        continue;
+      }
+      const text = extractTextFromContent(msg.content);
+      if (text) {
+        return text;
+      }
+    } catch {
+      // skip malformed
+    }
+  }
+  return null;
+}
+
 export function readLastMessagePreviewFromTranscript(
   sessionId: string,
   storePath: string | undefined,