Create worktrees in parallel to reduce startup latency for large -n values

[that-github-user]

Problem

In src/commands/run.ts, worktrees are created sequentially in a for loop:

for (let i = 1; i <= opts.attempts; i++) {
  const worktree = await git.createWorktree(repoRoot, `thinktank-${i}-...`);
  worktrees.push(worktree);
}

Each git worktree add call takes ~200-500ms. With -n 10, that's up to 5 seconds of setup before the first agent even starts.

Fix

Create all worktrees in parallel:

const worktrees = await Promise.all(
  Array.from({ length: opts.attempts }, (_, i) =>
    git.createWorktree(repoRoot, `thinktank-${i + 1}-${randomUUID().slice(0, 8)}`)
  )
);

Considerations

• Git itself serializes some worktree operations internally; parallelism gains are real but bounded
• Error handling: if one worktree creation fails, clean up all successfully created worktrees before throwing
• The existing cleanup path already handles partial lists

Benchmark target

With -n 5 on a mid-range machine, worktree setup time should drop from ~2s to ~600ms.

Acceptance criteria

• Worktrees are created with Promise.all in run.ts
• If any worktree creation fails, all already-created worktrees are cleaned up before the error is shown
• thinktank run -n 10 startup is measurably faster (documented in PR with before/after timing)
• Existing tests still pass

[that-github-user]

Fixed in #112. Worktrees created in parallel via Promise.all. Generated by thinktank Opus.