diff --git a/packages/server/src/server/agent/providers/claude/rewind-session-store.ts b/packages/server/src/server/agent/providers/claude/rewind-session-store.ts
new file mode 100644
index 0000000000..0b028cc927
--- /dev/null
+++ b/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"
+  );
+}
diff --git a/packages/server/src/server/agent/providers/claude/rewind-worker.ts b/packages/server/src/server/agent/providers/claude/rewind-worker.ts
new file mode 100644
index 0000000000..73c8d2b87a
--- /dev/null
+++ b/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);
+  }
+}
diff --git a/packages/server/src/server/agent/providers/claude/rewind.test.ts b/packages/server/src/server/agent/providers/claude/rewind.test.ts
index 226f41d39c..81d4ddcdb8 100644
--- a/packages/server/src/server/agent/providers/claude/rewind.test.ts
+++ b/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 () => {
diff --git a/packages/server/src/server/agent/providers/claude/rewind.ts b/packages/server/src/server/agent/providers/claude/rewind.ts
index 75607c184b..ebe192048a 100644
--- a/packages/server/src/server/agent/providers/claude/rewind.ts
+++ b/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})`)));
+  });
 }
 
 /**
diff --git a/packages/server/src/server/plugins/compiler.ts b/packages/server/src/server/plugins/compiler.ts
index b96c8ecd4e..183e5e754f 100644
--- a/packages/server/src/server/plugins/compiler.ts
+++ b/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.
diff --git a/packages/server/src/utils/test-fixtures/expand-tilde-worker.ts b/packages/server/src/utils/test-fixtures/expand-tilde-worker.ts
new file mode 100644
index 0000000000..2464dd4ac4
--- /dev/null
+++ b/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));
diff --git a/packages/server/src/utils/worker-entrypoint.test.ts b/packages/server/src/utils/worker-entrypoint.test.ts
new file mode 100644
index 0000000000..42e28b491a
--- /dev/null
+++ b/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"));
+  });
+});
diff --git a/packages/server/src/utils/worker-entrypoint.ts b/packages/server/src/utils/worker-entrypoint.ts
new file mode 100644
index 0000000000..a52343bc62
--- /dev/null
+++ b/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,
+  };
+}
diff --git a/scripts/trace-daemon-dist.test.mjs b/scripts/trace-daemon-dist.test.mjs
index a2c2149daa..5d086ae9e6 100644
--- a/scripts/trace-daemon-dist.test.mjs
+++ b/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 });
+  }
+});