refactor(test): extract createTempDir shared test helper

[kelsonpw]

Summary

• Adds a single shared createTempDir(prefix?) helper at src/utils/__tests__/helpers/temp-dir.ts that consolidates ~75 inlined fs.mkdtempSync(path.join(os.tmpdir(), 'prefix-')) + fs.rmSync(dir, { recursive: true, force: true }) blocks scattered across src/**/__tests__/.
• Migrates 27 test files (utils, frameworks, lib/session-checkpoint, lib/agent-state) to use the helper. Each call site preserves its prior beforeEach/afterEach semantics and any test-specific env-var stubbing — the helper only owns the temp directory itself.
• Helper has its own 5-test suite (temp-dir.test.ts) covering uniqueness, prefix normalisation, cleanup idempotency, and default-prefix behaviour.

Helper shape

export interface TempDirHandle {
  readonly dir: string;
  readonly cleanup: () => void;
}

export function createTempDir(prefix: string = 'wizard-test-'): TempDirHandle {
  const normalisedPrefix = prefix.endsWith('-') ? prefix : `${prefix}-`;
  const dir = fs.mkdtempSync(path.join(os.tmpdir(), normalisedPrefix));
  return {
    dir,
    cleanup: () => fs.rmSync(dir, { recursive: true, force: true }),
  };
}

I chose the { dir, cleanup } shape over a useTempDir flavour that auto-registers vitest hooks because (a) it maps 1:1 to the existing inline patterns — same number of lines, same scoping — and (b) several call sites need the dir inside an it() block with their own try/finally, which the auto-hook flavour wouldn't support cleanly.

Files migrated (27)

• utils (16): api-key-store, apply-lock, atomic-write, cleanup-shell-rc, debug, file-utils, install-id, last-used-selection, orchestrator-context, package-json-light, package-manager, port-detection, project-marker, setup-utils, storage-migration, storage-migration-exdev, storage-paths, update-notifier
• frameworks (10): django/utils, fastapi/utils, flask/utils, javascript-web/utils, javascript-web-wizard-agent, nextjs/utils, python/utils, python/detect-ignores-node-modules, python/preflight, vue/vue-wizard-agent
• lib (3): agent-state, agent-state-hydrate, session-checkpoint

Follow-up

~48 more test files still inline mkdtempSync. They're a mechanical migration to this same helper but stayed out of this PR to keep it reviewable; opening a follow-up issue/PR is straightforward.

Patterns NOT touched

• src/utils/wizard-abort.ts — out of scope per spec.
• Non-test source code — untouched.
• Non-mkdtempSync patterns (mock setup, env-var stubbing, snapshot teardown) — kept inline.
• The handful of mkdtempSync call sites that use ad-hoc prefixes inside it() blocks were migrated to inline createTempDir(...) + try/finally cleanup() calls, matching the file's existing style.

Test plan

• pnpm test — 4474/4474 pass (same count as baseline f49da82d).
• pnpm exec tsc --noEmit — clean.
• pnpm exec eslint on changed files — clean.
• Spot-checked pnpm exec vitest run --pool=forks --maxWorkers=1 for each migrated file as I went.
• wizard-abort.ts untouched (verified via git diff).
• Worktree at /tmp/test-helpers to be removed after merge.

---

Note

Low Risk
Low risk because changes are confined to test code and primarily refactor temp-dir setup/teardown, with a small new helper covered by dedicated unit tests.

Overview
Introduces a shared createTempDir(prefix?) test helper returning { dir, cleanup }, standardizing temp-directory creation and idempotent cleanup under os.tmpdir().

Refactors a large set of existing tests across CLI/commands/frameworks/lib/ui/utils to replace inline mkdtempSync/rmSync patterns with the helper (including cases with multiple temp dirs and try/finally cleanup), and adds a focused test suite validating prefix normalization, uniqueness, and cleanup behavior.

^{Reviewed by Cursor Bugbot for commit 424da78. Bugbot is set up for automated code reviews on this repo. Configure here.}