@@ -920,6 +920,54 @@ it.effect("retries a fetch that lost a ref update to another Git process", () =>
   }).pipe(Effect.provide(layerServerConfig.pipe(Layer.provideMerge(NodeServices.layer)))),
 );
 
+it.effect("lets a worktree checkout that is still working run past five minutes", () =>
+  Effect.gen(function* () {
+    const checkoutStarted = yield* Deferred.make<void>();
+    const checkoutFinished = yield* Deferred.make<void>();
+    const spawner = ChildProcessSpawner.make((command) =>
+      Effect.gen(function* () {
+        if (!ChildProcess.isStandardCommand(command))
+          return yield* Effect.die("expected Git command");
+        if (!command.args.includes("worktree")) return makeSuccessfulHandle("");
+        yield* Deferred.succeed(checkoutStarted, undefined);
+        return ChildProcessSpawner.makeHandle({
+          ...makeSuccessfulHandle(""),
+          exitCode: Deferred.await(checkoutFinished).pipe(
+            Effect.as(ChildProcessSpawner.ExitCode(0)),
+          ),
+          stderr: Stream.encodeText(
+            Stream.concat(
+              Stream.make("Updating files:  40% (49052/122629)\n"),
+              Stream.fromEffect(
+                Deferred.await(checkoutFinished).pipe(
+                  Effect.as("Updating files: 100% (122629/122629), done.\n"),
+                ),
+              ),
+            ),
+          ),
+        });
+      }),
+    );
+    const driver = yield* makeGitVcsDriverCore().pipe(
+      Effect.provideService(ChildProcessSpawner.ChildProcessSpawner, spawner),
+    );
+    const path = yield* Path.Path;
+    const cwd = yield* makeTmpDir();
+    const worktreePath = path.join(cwd, "worktree");
+
+    const creation = yield* driver
+      .createWorktree({ cwd, refName: "main", newRefName: "t3/slow-checkout", path: worktreePath })
+      .pipe(Effect.forkChild);
+    yield* Deferred.await(checkoutStarted);
+    yield* TestClock.adjust("6 minutes");
+    yield* Deferred.succeed(checkoutFinished, undefined);
+
+    const result = yield* Fiber.join(creation);
+    assert.equal(result.worktree.path, worktreePath);
+    assert.equal(result.worktree.refName, "t3/slow-checkout");
+  }).pipe(Effect.provide(layerServerConfig.pipe(Layer.provideMerge(NodeServices.layer)))),
+);
+
 describe("rejected git refs", () => {
   const remoteUrl = "https://user:[email protected]/org/secret-repo.git";
   const failedPush = `error: failed to push some refs to '${remoteUrl}'`;
 
@@ -62,7 +62,6 @@ const branchBaseConfigKey = (branch: string) => `branch.${branch}.t3-merge-base`
  */
 const legacyBranchBaseConfigKey = (branch: string) => `branch.${branch}.gh-merge-base`;
 const gitProcesses = Semaphore.makeUnsafe(8);
-const WORKTREE_ADD_TIMEOUT_MS = 300_000;
 const WORKTREE_REMOVE_TIMEOUT_MS = Duration.toMillis(Duration.minutes(5));
 const DEFAULT_MAX_OUTPUT_BYTES = 1_000_000;
 const OUTPUT_TRUNCATED_MARKER = "\n\n[truncated]";
@@ -3877,7 +3876,9 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
       ["-c", `checkout.workers=${checkoutWorkers}`, ...args],
       {
         fallbackErrorDetail: "git worktree add failed",
-        timeoutMs: WORKTREE_ADD_TIMEOUT_MS,
+        // Large checkouts and post-checkout hooks can legitimately run for many
+        // minutes; a fixed deadline kills them and leaves an orphaned worktree.
+        timeoutMs: null,
         ...(onCheckoutProgress
           ? {
               // Git only prints checkout progress when stderr is a tty or the