fix(claude): keep the daemon responsive during conversation rewind

The SDK parses and copies the complete transcript while forking a Claude
conversation. Running that work in the daemon's event loop blocks all
connected clients, even though only one conversation is being rewound.

Run the fork in a worker, stream transcript records, and append in bounded
chunks. Preserve the SDK's fork content, transcript location, and error
fields. Share the existing compiler worker loader and verify that the
installed daemon closure contains and starts the rewind worker.

Retain Dominic Anaeto's implementation and regressions from #8444, rebased
onto main to include the correction for the moved worktrees documentation
page in the website test.

Fixes #8209

Co-authored-by: Dominic Anaeto <dominic.anaeto@gmail.com>

.github/workflows/desktop-release.yml

@@ -135,6 +135,32 @@ jobs:
         env:
           NODE_AUTH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
+      # Backport electron-builder#10172 to the pinned build tool only.
+      # Remove this step when app-builder-lib is upgraded to a release containing it.
+      - name: Repair temporary keychain password in signing tool
+        shell: bash
+        run: |
+          node <<'KEYCHAIN_FIX'
+          const fs = require('node:fs');
+          const path = require('node:path');
+          const manifestPath = require.resolve('app-builder-lib/package.json');
+          if (JSON.parse(fs.readFileSync(manifestPath, 'utf8')).version !== '26.8.1') {
+            throw new Error('Reassess/remove the signing backport for the new app-builder-lib version');
+          }
+          const sourcePath = path.join(path.dirname(manifestPath), 'out/codeSign/macCodeSign.js');
+          let source = fs.readFileSync(sourcePath, 'utf8');
+          const replacements = [
+            ['importCerts(keychainFile, certPaths, cscPasswords)', 'importCerts(keychainFile, certPaths, cscPasswords, keychainPassword)'],
+            ['importCerts(keychainFile, paths, keyPasswords)', 'importCerts(keychainFile, paths, keyPasswords, keychainPassword)'],
+            ['["set-key-partition-list", "-S", "apple-tool:,apple:", "-s", "-k", password, keychainFile]', '["set-key-partition-list", "-S", "apple-tool:,apple:", "-s", "-k", keychainPassword, keychainFile]'],
+          ];
+          for (const [before, after] of replacements) {
+            if (source.split(before).length !== 2) throw new Error('Unexpected signing tool source; refusing to patch');
+            source = source.replace(before, after);
+          }
+          fs.writeFileSync(sourcePath, source);
+          KEYCHAIN_FIX
+
       - name: Set desktop package version from tag
         shell: bash
         run: |

nix/desktop-package.nix

@@ -127,7 +127,7 @@ buildNpmPackage {
         # The Nix output is not a distributable DMG, so leave it unsigned and
         # disable the hardened runtime that requires a matching signature.
         CSC_IDENTITY_AUTO_DISCOVERY=false \
-          npm exec --offline -- electron-builder \
+          ../../node_modules/.bin/electron-builder \
             --config electron-builder.yml \
             --dir \
             --mac \

nix/npm-deps.hash

@@ -1 +1 @@
-sha256-KN/AVZV/o0TleLLpmggSrdJqjFDJ/NJYVHiC54xb4jQ=
+sha256-CeT2PtYIAFwvBC9LIku8VkTl0pvKxYzSCn0QW2ManfU=

packages/app/e2e/browser/composer-recall.spec.ts

@@ -3,7 +3,7 @@ import {
   composerLocator,
   expectComposerDraft,
   expectComposerVisible,
-  fillComposerDraft,
+  submitMessage,
   typeIntoFocusedComposer,
 } from "../support/helpers/composer";
 import { openAgentRoute, seedMockAgentWorkspace } from "../support/helpers/mock-agent";
@@ -12,14 +12,8 @@ function userMessages(page: Page) {
   return page.getByTestId("user-message");
 }
 
-async function sendDraftWhenReady(page: Page) {
-  await expect(page.getByRole("button", { name: "Send message", exact: true })).toBeEnabled();
-  await pressInComposer(page, "Enter");
-}
-
 async function sendAndWaitForMessage(page: Page, text: string, expectedCount: number) {
-  await fillComposerDraft(page, text);
-  await sendDraftWhenReady(page);
+  await submitMessage(page, text);
   await expect(userMessages(page)).toHaveCount(expectedCount, { timeout: 30_000 });
   await expectComposerDraft(page, "");
 }
@@ -55,7 +49,7 @@ test.describe("Composer recall", () => {
       await pressInComposer(page, "ArrowUp");
       await expectComposerDraft(page, "add tests for login");
 
-      await sendDraftWhenReady(page);
+      await pressInComposer(page, "Enter");
       await expect(userMessages(page)).toHaveCount(3, { timeout: 30_000 });
       await expect(userMessages(page).last()).toContainText("add tests for login");
     } finally {

packages/desktop/package.json

@@ -41,7 +41,7 @@
     "@types/node": "24.6.0",
     "@types/ws": "^8.5.14",
     "electron": "44.2.0",
-    "electron-builder": "26.18.0",
+    "electron-builder": "26.8.1",
     "typescript": "5.9.3",
     "unzip-crx-3": "^0.2.0",
     "vitest": "^4.1.6",

packages/server/src/server/agent/providers/claude/agent.import-titles.test.ts

@@ -1,4 +1,3 @@
-import { constants as bufferConstants } from "node:buffer";
 import * as fs from "node:fs/promises";
 import * as os from "node:os";
 import * as path from "node:path";
@@ -237,64 +236,4 @@ describe("importing a renamed Claude session", () => {
 
     await expect(importSession(sessionId)).rejects.toThrow();
   });
-
-  test("reads the rename from a transcript too large to hold as one string", async () => {
-    const sessionId = "oversized-transcript";
-    const projectDir = claudeProjectDirSync(SESSION_CWD, { configDir });
-    await fs.mkdir(projectDir, { recursive: true });
-    const transcript = path.join(projectDir, `${sessionId}.jsonl`);
-    // A hole stands in for the long session this used to fail on: the file only
-    // has to be longer than a string can be, and the rename sits at its end.
-    await fs.writeFile(transcript, "");
-    await fs.truncate(transcript, bufferConstants.MAX_STRING_LENGTH + 1);
-    await fs.appendFile(
-      transcript,
-      `\n${[
-        userRecord({ sessionId, content: "Trace the slow query" }),
-        { type: "custom-title", customTitle: "Slow query hunt", sessionId },
-      ]
-        .map((record) => JSON.stringify(record))
-        .join("\n")}\n`,
-    );
-
-    const imported = await importSession(sessionId);
-
-    expect(imported.config.title).toBe("Slow query hunt");
-  });
-
-  test("reads the rename from behind more records than one read covers", async () => {
-    const sessionId = "late-records-rename";
-    await writeSession({
-      sessionId,
-      records: [
-        userRecord({ sessionId, content: "Review this project" }),
-        { type: "custom-title", customTitle: "Scrollback review", sessionId },
-        // One record longer than a single read, then enough records to leave the
-        // rename several reads back from the end of the file.
-        userRecord({ sessionId, content: "x".repeat(128 * 1024) }),
-        ...Array.from({ length: 64 }, (_, index) =>
-          userRecord({ sessionId, content: `${"y".repeat(4 * 1024)} ${index}` }),
-        ),
-      ],
-    });
-
-    const imported = await importSession(sessionId);
-
-    expect(imported.config.title).toBe("Scrollback review");
-  });
-
-  test("imports a large record after the last rename without repeatedly copying it", async () => {
-    const sessionId = "large-record-after-rename";
-    await writeSession({
-      sessionId,
-      records: [
-        { type: "custom-title", customTitle: "Large attachment review", sessionId },
-        userRecord({ sessionId, content: "x".repeat(96 * 1024 * 1024) }),
-      ],
-    });
-
-    const imported = await importSession(sessionId);
-
-    expect(imported.config.title).toBe("Large attachment review");
-  });
 });

packages/server/src/server/agent/providers/claude/agent.ts

@@ -6853,79 +6853,40 @@ function normalizeClaudeSessionTitle(title: string | null): string | null {
 }
 
 const CLAUDE_CUSTOM_TITLE_TYPE = "custom-title";
-const CLAUDE_CUSTOM_TITLE_NEEDLE = Buffer.from(`"${CLAUDE_CUSTOM_TITLE_TYPE}"`);
-const CLAUDE_TITLE_SCAN_CHUNK_BYTES = 64 * 1024;
-
-function readClaudeCustomTitleFromRecord(record: Buffer): string | null {
-  // The needle also matches a prompt that quotes it, so a record still has to
-  // parse as a `custom-title` entry carrying a usable name. Records without the
-  // needle are never decoded, so a long one costs a byte search and nothing more.
-  if (!record.includes(CLAUDE_CUSTOM_TITLE_NEEDLE)) {
-    return null;
-  }
-  let parsed: unknown;
-  try {
-    parsed = JSON.parse(record.toString("utf8").trim());
-  } catch {
-    return null;
-  }
-  const entry = toObjectRecord(parsed);
-  if (!entry || entry.isSidechain || entry.type !== CLAUDE_CUSTOM_TITLE_TYPE) {
-    return null;
-  }
-  return normalizeClaudeSessionTitle(
-    typeof entry.customTitle === "string" ? entry.customTitle : null,
-  );
-}
 
 /**
  * The `custom-title` record is re-emitted every time the session is saved, so
- * the current name is the last usable one in the file. Reading backwards a chunk
- * at a time finds it without walking the transcript, which matters because
- * sessions reach tens of megabytes, and never holds the file as one string, so a
- * transcript past V8's maximum string length still imports.
+ * the current name is the last usable one in the file. Searching backwards finds it without
+ * walking the transcript, which matters because sessions reach tens of
+ * megabytes.
  */
-async function readLastClaudeCustomTitle(filePath: string): Promise<string | null> {
-  const handle = await fsPromises.open(filePath, "r");
-  try {
-    const stats = await handle.stat();
-    if (!stats.isFile()) {
-      // Opening a directory succeeds on Windows even though reading it does not,
-      // so reject the way reading the transcript as a file would.
-      throw Object.assign(
-        new Error(`EISDIR: illegal operation on a directory, read '${filePath}'`),
-        { code: "EISDIR", path: filePath },
+function readLastClaudeCustomTitle(content: string): string | null {
+  const needle = `"${CLAUDE_CUSTOM_TITLE_TYPE}"`;
+  let at = content.lastIndexOf(needle);
+  while (at >= 0) {
+    const lineStart = content.lastIndexOf("\n", at) + 1;
+    const lineEnd = content.indexOf("\n", at);
+    const line = lineEnd === -1 ? content.slice(lineStart) : content.slice(lineStart, lineEnd);
+    let parsed: unknown;
+    try {
+      parsed = JSON.parse(line.trim());
+    } catch {
+      parsed = undefined;
+    }
+    const entry = toObjectRecord(parsed);
+    if (entry && !entry.isSidechain && entry.type === CLAUDE_CUSTOM_TITLE_TYPE) {
+      const title = normalizeClaudeSessionTitle(
+        typeof entry.customTitle === "string" ? entry.customTitle : null,
       );
-    }
-    let end = stats.size;
-    // Retain unfinished record pieces in reverse file order. Assemble each
-    // complete record once, so a large tool/image record costs linear work.
-    let pieces: Buffer[] = [];
-    while (end > 0) {
-      const length = Math.min(CLAUDE_TITLE_SCAN_CHUNK_BYTES, end);
-      const chunk = Buffer.alloc(length);
-      await handle.read(chunk, 0, length, end - length);
-      let recordEnd = chunk.length;
-      for (
-        let at = chunk.lastIndexOf(10);
-        at >= 0;
-        at = at === 0 ? -1 : chunk.lastIndexOf(10, at - 1)
-      ) {
-        pieces.push(chunk.subarray(at + 1, recordEnd));
-        const record = Buffer.concat(pieces.toReversed());
-        const title = readClaudeCustomTitleFromRecord(record);
-        if (title) return title;
-        pieces = [];
-        recordEnd = at;
+      if (title) {
+        return title;
       }
-      if (recordEnd > 0) pieces.push(chunk.subarray(0, recordEnd));
-      end -= length;
     }
-    // The first record in the file has no newline in front of it.
-    return readClaudeCustomTitleFromRecord(Buffer.concat(pieces.toReversed()));
-  } finally {
-    await handle.close();
+    // The needle also matches a prompt that quotes it, and a record can carry no
+    // usable name, so keep looking backwards for one that does.
+    at = at <= 0 ? -1 : content.lastIndexOf(needle, at - 1);
   }
+  return null;
 }
 
 function isErrnoException(error: unknown): error is NodeJS.ErrnoException {
@@ -6937,8 +6898,9 @@ async function readClaudeRenamedSessionTitle(input: {
   sessionId: string;
   configDir: string;
 }): Promise<string | null> {
+  let content: string;
   try {
-    return await readLastClaudeCustomTitle(await claudeTranscriptPath(input));
+    content = await fsPromises.readFile(await claudeTranscriptPath(input), "utf8");
   } catch (error) {
     // A session with no transcript on disk has no rename to carry over. Every
     // other read failure is a real fault and stays explicit.
@@ -6947,6 +6909,7 @@ async function readClaudeRenamedSessionTitle(input: {
     }
     throw error;
   }
+  return readLastClaudeCustomTitle(content);
 }
 
 function normalizeImportablePromptPreview(text: string): string | null {

packages/server/src/server/agent/providers/claude/rewind-session-store.ts

@@ -0,0 +1,63 @@
+import { createReadStream } from "node:fs";
+import { appendFile } from "node:fs/promises";
+import path from "node:path";
+import { createInterface } from "node:readline";
+import type { SessionStore, SessionStoreEntry } from "@anthropic-ai/claude-agent-sdk";
+
+const APPEND_CHUNK_LENGTH = 1 << 20;
+
+export function projectFolderSessionStore(projectFolder: string): SessionStore {
+  const transcriptPath = (sessionId: string) => path.join(projectFolder, `${sessionId}.jsonl`);
+  return {
+    async load({ sessionId }) {
+      const input = createReadStream(transcriptPath(sessionId), { encoding: "utf8" });
+      const lines = createInterface({ input, crlfDelay: Infinity });
+      const entries: SessionStoreEntry[] = [];
+      try {
+        for await (const line of lines) {
+          const entry = parseTranscriptEntry(line);
+          if (entry) entries.push(entry);
+        }
+      } catch (error) {
+        if ((error as NodeJS.ErrnoException).code === "ENOENT") return null;
+        throw error;
+      } finally {
+        lines.close();
+        input.destroy();
+      }
+      return entries;
+    },
+    async append({ sessionId }, entries) {
+      let chunk = "";
+      for (const entry of entries) {
+        chunk += `${JSON.stringify(entry)}\n`;
+        if (chunk.length >= APPEND_CHUNK_LENGTH) {
+          await appendFile(transcriptPath(sessionId), chunk, "utf8");
+          chunk = "";
+        }
+      }
+      await appendFile(transcriptPath(sessionId), chunk, "utf8");
+    },
+  };
+}
+
+function parseTranscriptEntry(line: string): SessionStoreEntry | null {
+  if (!line.trim()) return null;
+  let parsed: unknown;
+  try {
+    parsed = JSON.parse(line);
+  } catch {
+    // Skip a line that is not JSON, as the SDK's own transcript reader does.
+    return null;
+  }
+  return isSessionStoreEntry(parsed) ? parsed : null;
+}
+
+function isSessionStoreEntry(value: unknown): value is SessionStoreEntry {
+  return (
+    typeof value === "object" &&
+    value !== null &&
+    !Array.isArray(value) &&
+    typeof (value as { type?: unknown }).type === "string"
+  );
+}

packages/server/src/server/agent/providers/claude/rewind-worker.ts

@@ -0,0 +1,43 @@
+import path from "node:path";
+import { parentPort, workerData } from "node:worker_threads";
+import { forkSession } from "@anthropic-ai/claude-agent-sdk";
+import { projectFolderSessionStore } from "./rewind-session-store.js";
+
+export interface ClaudeForkRequest {
+  sessionId: string;
+  upToMessageId: string;
+  transcriptPath: string;
+}
+
+export type ClaudeForkReply =
+  | { kind: "forked"; sessionId: string }
+  | {
+      kind: "failed";
+      message: string;
+      stack: string | undefined;
+      properties: Record<string, unknown>;
+    };
+
+const port = parentPort!;
+const request: ClaudeForkRequest = workerData;
+try {
+  // On its own, the SDK looks for the session under the daemon's CLAUDE_CONFIG_DIR, while a
+  // provider can point Claude Code at another one. Forking through a store rooted at the
+  // transcript's folder reads the session where Claude Code wrote it and writes the fork beside it.
+  const fork = await forkSession(request.sessionId, {
+    upToMessageId: request.upToMessageId,
+    sessionStore: projectFolderSessionStore(path.dirname(request.transcriptPath)),
+  });
+  port.postMessage({ kind: "forked", sessionId: fork.sessionId } satisfies ClaudeForkReply);
+} catch (cause) {
+  const error = cause instanceof Error ? cause : new Error(String(cause));
+  const failure = { kind: "failed", message: error.message, stack: error.stack } as const;
+  try {
+    port.postMessage({ ...failure, properties: { ...error } } satisfies ClaudeForkReply);
+  } catch (cloneError) {
+    if (!(cloneError instanceof DOMException) || cloneError.name !== "DataCloneError") {
+      throw cloneError;
+    }
+    port.postMessage({ ...failure, properties: {} } satisfies ClaudeForkReply);
+  }
+}

packages/server/src/server/agent/providers/claude/rewind.test.ts

@@ -1,4 +1,5 @@
 import { randomUUID } from "node:crypto";
+import { subscribe, unsubscribe } from "node:diagnostics_channel";
 import {
   mkdirSync,
   mkdtempSync,
@@ -10,9 +11,11 @@ import {
 } from "node:fs";
 import { tmpdir } from "node:os";
 import path from "node:path";
+import { Worker } from "node:worker_threads";
 import { afterEach, describe, expect, test } from "vitest";
-import type { Query } from "@anthropic-ai/claude-agent-sdk";
+import { forkSession, type Query } from "@anthropic-ai/claude-agent-sdk";
 
+import { measureMainThreadWork } from "../../../../test-utils/main-thread-work.js";
 import {
   findSteeredMessageParent,
   revertClaudeConversation,
@@ -20,6 +23,7 @@ import {
   revertClaudeFiles,
   realClaudeRewindSdk,
 } from "./rewind.js";
+import { projectFolderSessionStore } from "./rewind-session-store.js";
 import { FakeClaudeSdk } from "./test-rewind-claude-sdk.js";
 
 describe("Claude rewind", () => {
@@ -278,8 +282,196 @@ describe("Claude rewind against the Claude SDK", () => {
       "tool output",
     ]);
   });
+
+  test("writes the fork beside the original and leaves the original untouched", async () => {
+    tempRoot = mkdtempSync(path.join(tmpdir(), "claude-rewind-fork-"));
+    const projectDir = path.join(tempRoot, "projects", "-repo");
+    mkdirSync(projectDir, { recursive: true });
+    const sessionId = randomUUID();
+    const firstUser = randomUUID();
+    const firstReply = randomUUID();
+    const secondUser = randomUUID();
+    const transcriptPath = path.join(projectDir, `${sessionId}.jsonl`);
+    writeTranscript(transcriptPath, sessionId, [
+      { type: "user", uuid: firstUser, parentUuid: null, text: "first" },
+      { type: "assistant", uuid: firstReply, parentUuid: firstUser, text: "first reply" },
+      { type: "user", uuid: secondUser, parentUuid: firstReply, text: "second" },
+      { type: "assistant", uuid: randomUUID(), parentUuid: secondUser, text: "second reply" },
+    ]);
+    const original = readFileSync(transcriptPath, "utf8");
+
+    const fork = await realClaudeRewindSdk.forkSession(sessionId, {
+      upToMessageId: secondUser,
+      transcriptPath,
+    });
+
+    const forkPath = path.join(projectDir, `${fork.sessionId}.jsonl`);
+    expect(readdirSync(projectDir).sort()).toEqual(
+      [`${sessionId}.jsonl`, `${fork.sessionId}.jsonl`].sort(),
+    );
+    expect(readMessageTexts(forkPath)).toEqual(["first", "first reply", "second"]);
+    const forkSessionIds = readFileSync(forkPath, "utf8")
+      .trim()
+      .split("\n")
+      .map((line) => (JSON.parse(line) as { sessionId: string }).sessionId);
+    expect(forkSessionIds).toEqual([
+      fork.sessionId,
+      fork.sessionId,
+      fork.sessionId,
+      fork.sessionId,
+    ]);
+    expect(readFileSync(transcriptPath, "utf8")).toBe(original);
+  });
+
+  test("rejects with the SDK's own error when the transcript is missing", async () => {
+    tempRoot = mkdtempSync(path.join(tmpdir(), "claude-rewind-missing-"));
+    const sessionId = randomUUID();
+
+    await expect(
+      realClaudeRewindSdk.forkSession(sessionId, {
+        upToMessageId: randomUUID(),
+        transcriptPath: path.join(tempRoot, `${sessionId}.jsonl`),
+      }),
+    ).rejects.toThrow(new Error(`Session ${sessionId} not found`));
+  });
+
+  test("rejects with the name and message of the error the SDK raises", async () => {
+    tempRoot = mkdtempSync(path.join(tmpdir(), "claude-rewind-invalid-"));
+    const sessionId = randomUUID();
+    const sdkError = await forkSession(sessionId, { upToMessageId: "not-a-uuid" }).then(
+      () => null,
+      (error: Error) => error,
+    );
+    expect(sdkError).toBeInstanceOf(Error);
+
+    await expect(
+      realClaudeRewindSdk.forkSession(sessionId, {
+        upToMessageId: "not-a-uuid",
+        transcriptPath: path.join(tempRoot, `${sessionId}.jsonl`),
+      }),
+    ).rejects.toMatchObject({ name: sdkError?.name, message: sdkError?.message });
+  });
+
+  test("keeps a filesystem error's code when the fork fails in the worker", async () => {
+    tempRoot = mkdtempSync(path.join(tmpdir(), "claude-rewind-eisdir-"));
+    const sessionId = randomUUID();
+    const transcriptPath = path.join(tempRoot, `${sessionId}.jsonl`);
+    mkdirSync(transcriptPath);
+
+    await expect(
+      realClaudeRewindSdk.forkSession(sessionId, { upToMessageId: randomUUID(), transcriptPath }),
+    ).rejects.toMatchObject({ name: "Error", code: "EISDIR" });
+  });
+
+  test("forks one conversation at a time", async () => {
+    tempRoot = mkdtempSync(path.join(tmpdir(), "claude-rewind-queue-"));
+    const projectDir = path.join(tempRoot, "projects", "-repo");
+    mkdirSync(projectDir, { recursive: true });
+    const forks = [randomUUID(), randomUUID()].map((sessionId) => {
+      const user = randomUUID();
+      const transcriptPath = path.join(projectDir, `${sessionId}.jsonl`);
+      writeTranscript(transcriptPath, sessionId, [
+        { type: "user", uuid: user, parentUuid: null, text: "first" },
+        { type: "assistant", uuid: randomUUID(), parentUuid: user, text: "first reply" },
+      ]);
+      return { sessionId, upToMessageId: user, transcriptPath };
+    });
+    const events: string[] = [];
+    let started = 0;
+    function recordWorker(message: unknown): void {
+      if (typeof message !== "object" || message === null || !("worker" in message)) return;
+      if (!(message.worker instanceof Worker)) return;
+      const fork = ++started;
+      events.push(`start ${fork}`);
+      message.worker.once("message", () => events.push(`reply ${fork}`));
+    }
+
+    subscribe("worker_threads", recordWorker);
+    try {
+      await Promise.all(
+        forks.map(({ sessionId, upToMessageId, transcriptPath }) =>
+          realClaudeRewindSdk.forkSession(sessionId, { upToMessageId, transcriptPath }),
+        ),
+      );
+    } finally {
+      unsubscribe("worker_threads", recordWorker);
+    }
+
+    expect(events).toEqual(["start 1", "reply 1", "start 2", "reply 2"]);
+  });
+
+  test("forks a long transcript without blocking the daemon's event loop", async () => {
+    tempRoot = mkdtempSync(path.join(tmpdir(), "claude-rewind-long-"));
+    const projectDir = path.join(tempRoot, "projects", "-repo");
+    mkdirSync(projectDir, { recursive: true });
+    const sessionId = randomUUID();
+    const transcriptPath = path.join(projectDir, `${sessionId}.jsonl`);
+    const turns = 43_000;
+    const lastUser = writeLongTranscript(transcriptPath, sessionId, turns);
+
+    const { result: fork, blockingMs } = await measureMainThreadWork(
+      "claude fork main-thread work",
+      () => realClaudeRewindSdk.forkSession(sessionId, { upToMessageId: lastUser, transcriptPath }),
+    );
+
+    expect(blockingMs).toBeLessThan(50);
+    const forkLines = readFileSync(path.join(projectDir, `${fork.sessionId}.jsonl`), "utf8")
+      .trim()
+      .split("\n");
+    expect(forkLines).toHaveLength(turns * 2);
+    expect(JSON.parse(forkLines[turns * 2 - 2]!).forkedFrom).toEqual({
+      sessionId,
+      messageUuid: lastUser,
+    });
+  });
 });
 
+describe("Claude project folder session store", () => {
+  let root: string | null = null;
+
+  afterEach(() => {
+    if (root) rmSync(root, { recursive: true, force: true });
+    root = null;
+  });
+
+  test("appends entries after existing ones, byte for byte, and loads them back", async () => {
+    root = mkdtempSync(path.join(tmpdir(), "claude-rewind-store-"));
+    const store = projectFolderSessionStore(root);
+    const key = { projectKey: "-repo", sessionId: randomUUID() };
+    const transcriptPath = path.join(root, `${key.sessionId}.jsonl`);
+    const existing = { type: "user", uuid: randomUUID(), message: { content: "already there" } };
+    writeFileSync(transcriptPath, `${JSON.stringify(existing)}\n`);
+    const entries = Array.from({ length: 4_000 }, (_, index) => ({
+      type: "assistant",
+      uuid: randomUUID(),
+      message: { content: `reply ${index} ✓ ${"x".repeat(1_000)}` },
+    }));
+
+    await store.append(key, entries);
+
+    expect(readFileSync(transcriptPath, "utf8")).toBe(
+      [existing, ...entries].map((entry) => `${JSON.stringify(entry)}\n`).join(""),
+    );
+    expect(await store.load(key)).toEqual([existing, ...entries]);
+  });
+});
+
+function writeLongTranscript(transcriptPath: string, sessionId: string, turns: number): string {
+  const toolOutput = 'line 1: "quoted" output\twith\\escapes\n'.repeat(4);
+  const lines: TranscriptLine[] = [];
+  let parentUuid: string | null = null;
+  let lastUser = "";
+  for (let turn = 0; turn < turns; turn++) {
+    lastUser = randomUUID();
+    const reply = randomUUID();
+    lines.push({ type: "user", uuid: lastUser, parentUuid, text: `question ${turn}` });
+    lines.push({ type: "assistant", uuid: reply, parentUuid: lastUser, text: toolOutput });
+    parentUuid = reply;
+  }
+  writeTranscript(transcriptPath, sessionId, lines);
+  return lastUser;
+}
+
 test.runIf(process.platform === "linux")(
   "releases the transcript descriptor after an early steer match",
   async () => {

packages/server/src/server/agent/providers/claude/rewind.ts

@@ -1,13 +1,10 @@
 import { createReadStream } from "node:fs";
-import { appendFile, readFile } from "node:fs/promises";
-import path from "node:path";
 import { createInterface } from "node:readline";
-import {
-  forkSession as claudeForkSession,
-  type Query,
-  type SessionStore,
-  type SessionStoreEntry,
-} from "@anthropic-ai/claude-agent-sdk";
+import { Worker } from "node:worker_threads";
+import type { Query } from "@anthropic-ai/claude-agent-sdk";
+import pLimit from "p-limit";
+import { resolveWorkerEntrypoint } from "../../../../utils/worker-entrypoint.js";
+import type { ClaudeForkReply, ClaudeForkRequest } from "./rewind-worker.js";
 
 export interface ClaudeRewindSdk {
   forkSession(
@@ -16,60 +13,42 @@ export interface ClaudeRewindSdk {
   ): Promise<{ sessionId: string }>;
 }
 
-// On its own, the SDK looks for the session under the daemon's CLAUDE_CONFIG_DIR, while a
-// provider can point Claude Code at another one. Forking through a store rooted at the
-// transcript's folder reads the session where Claude Code wrote it and writes the fork beside it.
+const source = import.meta.url.endsWith(".ts");
+const workerUrl = new URL(source ? "./rewind-worker.ts" : "./rewind-worker.js", import.meta.url);
+const rewindWorker = resolveWorkerEntrypoint(workerUrl);
+const forks = pLimit(1);
+
 export const realClaudeRewindSdk: ClaudeRewindSdk = {
   forkSession: (sessionId, options) =>
-    claudeForkSession(sessionId, {
-      upToMessageId: options.upToMessageId,
-      sessionStore: projectFolderSessionStore(path.dirname(options.transcriptPath)),
-    }),
+    forks(() =>
+      forkInWorker({
+        sessionId,
+        upToMessageId: options.upToMessageId,
+        transcriptPath: options.transcriptPath,
+      }),
+    ),
 };
 
-function projectFolderSessionStore(projectFolder: string): SessionStore {
-  const transcriptPath = (sessionId: string) => path.join(projectFolder, `${sessionId}.jsonl`);
-  return {
-    async load({ sessionId }) {
-      let text: string;
-      try {
-        text = await readFile(transcriptPath(sessionId), "utf8");
-      } catch (error) {
-        if ((error as NodeJS.ErrnoException).code === "ENOENT") return null;
-        throw error;
+function forkInWorker(request: ClaudeForkRequest): Promise<{ sessionId: string }> {
+  return new Promise((resolve, reject) => {
+    const worker = new Worker(rewindWorker.entrypoint, {
+      eval: rewindWorker.eval,
+      execArgv: [],
+      workerData: request,
+    });
+    worker.once("message", (reply: ClaudeForkReply) => {
+      void worker.terminate();
+      if (reply.kind === "forked") {
+        resolve({ sessionId: reply.sessionId });
+        return;
       }
-      return parseTranscriptEntries(text);
-    },
-    async append({ sessionId }, entries) {
-      const lines = entries.map((entry) => `${JSON.stringify(entry)}\n`).join("");
-      await appendFile(transcriptPath(sessionId), lines, "utf8");
-    },
-  };
-}
-
-function parseTranscriptEntries(text: string): SessionStoreEntry[] {
-  const entries: SessionStoreEntry[] = [];
-  for (const line of text.split("\n")) {
-    if (!line.trim()) continue;
-    let parsed: unknown;
-    try {
-      parsed = JSON.parse(line);
-    } catch {
-      // Skip a line that is not JSON, as the SDK's own transcript reader does.
-      continue;
-    }
-    if (isSessionStoreEntry(parsed)) entries.push(parsed);
-  }
-  return entries;
-}
-
-function isSessionStoreEntry(value: unknown): value is SessionStoreEntry {
-  return (
-    typeof value === "object" &&
-    value !== null &&
-    !Array.isArray(value) &&
-    typeof (value as { type?: unknown }).type === "string"
-  );
+      const error = new Error(reply.message);
+      error.stack = reply.stack;
+      reject(Object.assign(error, reply.properties));
+    });
+    worker.once("error", reject);
+    worker.once("exit", (code) => reject(new Error(`Claude rewind worker exited (code ${code})`)));
+  });
 }
 
 /**

packages/server/src/server/plugins/compiler.ts

@@ -1,8 +1,7 @@
-import { createRequire } from "node:module";
-import { pathToFileURL } from "node:url";
 import { Worker } from "node:worker_threads";
 import pLimit from "p-limit";
 import { ZodError } from "zod";
+import { resolveWorkerEntrypoint } from "../../utils/worker-entrypoint.js";
 import type * as build from "./compiler-build.js";
 import type { PluginManifest } from "./manifest.js";
 import type { CompilerReply } from "./compiler-worker.js";
@@ -37,9 +36,7 @@ const workerUrl = new URL(
 );
 // Resolve the development loader once at module initialization, never during a
 // compile request. Packaged workers execute ordinary JavaScript without tsx.
-const workerEntrypoint = source
-  ? `import(${JSON.stringify(pathToFileURL(createRequire(import.meta.url).resolve("tsx/esm/api")).href)}).then(({ register }) => { register(); return import(${JSON.stringify(workerUrl.href)}); });`
-  : workerUrl;
+const compilerWorker = resolveWorkerEntrypoint(workerUrl);
 
 // Reuse the isolate during a build batch (notably daemon bootstrap), then release
 // TypeScript's heap when idle. Only this owner admits work or stops the worker.
@@ -74,7 +71,10 @@ class PluginCompiler {
   }
 
   private startWorker(): Worker {
-    const worker = new Worker(workerEntrypoint, { eval: source, execArgv: [] });
+    const worker = new Worker(compilerWorker.entrypoint, {
+      eval: compilerWorker.eval,
+      execArgv: [],
+    });
     this.worker = worker;
     // Keep error/exit ownership while idle too. The next caller gets a fresh
     // isolate after a crash; author build commands are never retried.

packages/server/src/utils/test-fixtures/expand-tilde-worker.ts

@@ -0,0 +1,6 @@
+import { parentPort, workerData } from "node:worker_threads";
+import { expandTilde } from "../path.js";
+
+const port = parentPort!;
+const input: string = workerData;
+port.postMessage(expandTilde(input));

packages/server/src/utils/worker-entrypoint.test.ts

@@ -0,0 +1,34 @@
+import { once } from "node:events";
+import { Worker } from "node:worker_threads";
+import { describe, expect, test } from "vitest";
+
+import { expandTilde } from "./path.js";
+import { resolveWorkerEntrypoint } from "./worker-entrypoint.js";
+
+describe("worker entrypoint", () => {
+  test("starts a compiled worker from its own URL", () => {
+    const entry = resolveWorkerEntrypoint(
+      new URL("file:///app/dist/server/server/plugins/compiler-worker.js"),
+    );
+
+    expect({ ...entry, entrypoint: String(entry.entrypoint) }).toEqual({
+      entrypoint: "file:///app/dist/server/server/plugins/compiler-worker.js",
+      eval: false,
+    });
+  });
+
+  test("runs a TypeScript worker, with its .js imports, through tsx", async () => {
+    const entry = resolveWorkerEntrypoint(
+      new URL("./test-fixtures/expand-tilde-worker.ts", import.meta.url),
+    );
+    const worker = new Worker(entry.entrypoint, {
+      eval: entry.eval,
+      execArgv: [],
+      workerData: "~/project",
+    });
+
+    const [expanded] = await once(worker, "message");
+
+    expect(expanded).toBe(expandTilde("~/project"));
+  });
+});

packages/server/src/utils/worker-entrypoint.ts

@@ -0,0 +1,16 @@
+import { createRequire } from "node:module";
+import { pathToFileURL } from "node:url";
+
+export interface WorkerEntrypoint {
+  entrypoint: string | URL;
+  eval: boolean;
+}
+
+export function resolveWorkerEntrypoint(workerUrl: URL): WorkerEntrypoint {
+  if (!workerUrl.pathname.endsWith(".ts")) return { entrypoint: workerUrl, eval: false };
+  const tsxUrl = pathToFileURL(createRequire(import.meta.url).resolve("tsx/esm/api")).href;
+  return {
+    entrypoint: `import(${JSON.stringify(tsxUrl)}).then(({ register }) => { register(); return import(${JSON.stringify(workerUrl.href)}); });`,
+    eval: true,
+  };
+}

scripts/ci-workflow.test.mjs

@@ -680,46 +680,51 @@ test("macOS jobs use latest runners while preserving release architectures", ()
   assert.match(release, /runner: macos-26-intel\n\s+electron_arch: x64/);
 });
 
-test("Nix desktop packaging resolves the workspace-local builder", () => {
-  const source = readFileSync(new URL("nix/desktop-package.nix", repoRoot), "utf8");
-  const invocation = source.match(/^\s+([^\n]*electron-builder) \\\n/m)?.[1];
-  assert.ok(invocation, "Nix invokes the desktop packaging tool");
-  const directory = mkdtempSync(join(tmpdir(), "nix-builder-resolution-"));
+test("macOS signing repair keeps certificate and keychain passwords separate", () => {
+  const workflow = readFileSync(new URL(".github/workflows/desktop-release.yml", repoRoot), "utf8");
+  const match = workflow.match(/<<'KEYCHAIN_FIX'\n([\s\S]*?)\n          KEYCHAIN_FIX/);
+  assert.ok(match, "the release workflow repairs the pinned signing tool");
+  const script = match[1].replace(/^          /gm, "");
+  const original = [
+    "return await importCerts(keychainFile, certPaths, cscPasswords);",
+    "async function importCerts(keychainFile, paths, keyPasswords) {",
+    '["import", paths[i], "-P", password]',
+    '["set-key-partition-list", "-S", "apple-tool:,apple:", "-s", "-k", password, keychainFile]',
+    "}",
+  ].join("\n");
+  const directory = mkdtempSync(join(tmpdir(), "signing-repair-"));
   try {
-    const desktop = join(directory, "packages/desktop");
-    mkdirSync(join(desktop, "node_modules/.bin"), { recursive: true });
-    mkdirSync(join(desktop, "node_modules/electron-builder"));
-    writeFileSync(
-      join(desktop, "node_modules/electron-builder/package.json"),
-      JSON.stringify({
-        name: "electron-builder",
-        version: "1.0.0",
-        bin: { "electron-builder": "../.bin/electron-builder" },
-      }),
-    );
-    writeFileSync(
-      join(directory, "package.json"),
-      JSON.stringify({ private: true, workspaces: ["packages/desktop"] }),
-    );
-    writeFileSync(
-      join(desktop, "package.json"),
-      JSON.stringify({
-        name: "desktop-fixture",
-        private: true,
-        devDependencies: { "electron-builder": "1.0.0" },
-      }),
-    );
-    writeFileSync(
-      join(desktop, "node_modules/.bin/electron-builder"),
-      '#!/bin/sh\nprintf "workspace-builder\\n"\n',
-      { mode: 0o755 },
-    );
-    const result = spawnSync("sh", ["-c", `${invocation} --version`], {
-      cwd: desktop,
-      encoding: "utf8",
-    });
-    assert.equal(result.status, 0, result.stderr);
-    assert.equal(result.stdout.trim(), "workspace-builder");
+    const packageDirectory = join(directory, "node_modules/app-builder-lib");
+    mkdirSync(join(packageDirectory, "out/codeSign"), { recursive: true });
+    const manifest = join(packageDirectory, "package.json");
+    const sourcePath = join(packageDirectory, "out/codeSign/macCodeSign.js");
+    for (const [version, source, succeeds] of [
+      ["26.8.1", original, true],
+      ["26.8.1", original.replace("cscPasswords);", "differentArguments);"), false],
+      ["26.18.0", original, false],
+    ]) {
+      writeFileSync(manifest, JSON.stringify({ name: "app-builder-lib", version }));
+      writeFileSync(sourcePath, source);
+      const result = spawnSync(process.execPath, ["-e", script], {
+        cwd: directory,
+        encoding: "utf8",
+      });
+      const actual = readFileSync(sourcePath, "utf8");
+      if (succeeds) {
+        assert.equal(result.status, 0, result.stderr);
+        assert.ok(
+          actual.includes("importCerts(keychainFile, certPaths, cscPasswords, keychainPassword)"),
+        );
+        assert.ok(
+          actual.includes("importCerts(keychainFile, paths, keyPasswords, keychainPassword)"),
+        );
+        assert.ok(actual.includes('["import", paths[i], "-P", password]'));
+        assert.ok(actual.includes('"-k", keychainPassword, keychainFile]'));
+      } else {
+        assert.notEqual(result.status, 0);
+        assert.equal(actual, source, "unexpected tool inputs must fail without a partial write");
+      }
+    }
   } finally {
     rmSync(directory, { recursive: true, force: true });
   }

scripts/trace-daemon-dist.test.mjs

@@ -1,6 +1,7 @@
 import assert from "node:assert/strict";
 import { execFile } from "node:child_process";
-import { cp, mkdtemp, rm } from "node:fs/promises";
+import { randomUUID } from "node:crypto";
+import { cp, mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
 import test from "node:test";
@@ -9,6 +10,12 @@ import { promisify } from "node:util";
 
 const repoRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
 const bridgeModule = "packages/server/dist/server/server/agent/providers/opencode/bridge.js";
+const claudeDist = "packages/server/dist/server/server/agent/providers/claude";
+const workerThreadEntrypoints = [
+  "packages/server/dist/server/server/plugins/compiler-worker.js",
+  `${claudeDist}/rewind-worker.js`,
+  `${claudeDist}/rewind-session-store.js`,
+];
 
 // Mirrors nix/package.nix's installPhase: copy every traced path into $out.
 async function installTracedDaemon(outRoot) {
@@ -17,12 +24,14 @@ async function installTracedDaemon(outRoot) {
     [path.join(repoRoot, "scripts/trace-daemon.mjs")],
     { cwd: repoRoot, maxBuffer: 64 * 1024 * 1024 },
   );
-  for (const file of stdout.split("\n").filter(Boolean)) {
+  const files = stdout.split("\n").filter(Boolean);
+  for (const file of files) {
     await cp(path.join(repoRoot, file), path.join(outRoot, file), {
       recursive: true,
       verbatimSymlinks: true,
     });
   }
+  return files;
 }
 
 test("traced daemon closure ships the OpenCode bridge plugin for every OpenCode version", async () => {
@@ -44,3 +53,32 @@ test("traced daemon closure ships the OpenCode bridge plugin for every OpenCode
     await rm(outRoot, { recursive: true, force: true });
   }
 });
+
+test("traced daemon closure ships the worker-thread entrypoints and what they load", async () => {
+  const outRoot = await mkdtemp(path.join(os.tmpdir(), "trace-daemon-dist-"));
+  try {
+    const files = await installTracedDaemon(outRoot);
+    for (const file of workerThreadEntrypoints) {
+      assert.ok(files.includes(file), `${file} is missing from the traced closure`);
+    }
+
+    const { realClaudeRewindSdk } = await import(
+      pathToFileURL(path.join(outRoot, claudeDist, "rewind.js")).href
+    );
+    const sessionId = randomUUID();
+    const user = randomUUID();
+    const transcriptPath = path.join(outRoot, `${sessionId}.jsonl`);
+    await writeFile(
+      transcriptPath,
+      `${JSON.stringify({ type: "user", uuid: user, parentUuid: null, sessionId, message: { role: "user", content: "first" } })}\n`,
+    );
+    const fork = await realClaudeRewindSdk.forkSession(sessionId, {
+      upToMessageId: user,
+      transcriptPath,
+    });
+    const forked = await readFile(path.join(outRoot, `${fork.sessionId}.jsonl`), "utf8");
+    assert.equal(JSON.parse(forked.split("\n")[0]).forkedFrom.messageUuid, user);
+  } finally {
+    await rm(outRoot, { recursive: true, force: true });
+  }
+});