Add local file picker API (codex)

[numnx]

🧩 Task: Add local file picker API

Automated task PR opened by Code UX for T01.

📋 Summary

Sprint: Sprint 139 · Settings mcp and & custom container · Task: T01

Improve Settings so operators can configure HTTP MCP servers with clear guidance and choose a custom container setup script through a file-picker field.

📝 Full Task Prompt

## Objective
Add a backend and dashboard API contract for browsing local files so settings can select a custom container setup script without free-typing every path.

## Scope
- `src/server/local-directory-routes.ts`
- `src/contracts/app-types.ts` `LocalDirectoryBrowserResponse` or a new adjacent response type
- `dashboard/src/types.ts` and `dashboard/src/v2/types.ts` re-exported local browser types
- `dashboard/src/v2/lib/project-api.ts`
- `tests/backend/server/local-directory-routes.test.ts`

## Implementation Requirements
1. Extend the local browser route surface with a file-capable endpoint, preferably `GET /api/local-files`, reusing the same allowed-root resolution, home/cwd/configured-root policy, path expansion, realpath containment checks, and sanitized error behavior as `/api/local-directories`.
2. Return directory navigation metadata plus sorted `directories` and sorted `files`, where each file entry includes at least `name` and absolute `path`; do not include file contents.
3. Add a typed dashboard API helper such as `fetchLocalFiles(directoryPath?: string)` in `dashboard/src/v2/lib/project-api.ts` and shared response types in the existing dashboard type re-export path.
4. Add backend tests covering directory and file listing, alphabetical sorting, access denial outside allowed roots, sanitized errors for missing paths, and the existing `/api/local-directories` behavior remaining unchanged.
5. Update `docs/settings/configuration-and-storage.md` to mention that the settings UI can browse allowed local roots for setup script paths and that the endpoint lists names/paths only.

## Constraints
- Do not expose arbitrary filesystem access outside home, current working directory, or `CODE_UX_DIRECTORY_BROWSER_ROOTS`.
- Do not return file contents, file sizes that are not needed, secrets, or unsanitized rejected paths.
- Preserve the existing `/api/local-directories` response shape for project directory picking.
- Keep the route cross-platform; do not assume POSIX path separators or executable extensions.

## Verification
- Run `pnpm exec vitest run tests/backend/server/local-directory-routes.test.ts`.
- Run `pnpm run lint`.
- Success means `/api/local-files` returns selectable files under allowed roots, denied paths return sanitized errors, and existing directory-picker tests still pass.

✅ QA Review

⏳ QA review runs after this PR is opened. Check the task card in the dashboard for the outcome once it lands.

🤖 Model & Provider

Provider	Codex CLI
Model	gpt-5.5

⏱️ Timing

Started	2026-07-06 09:48:48 UTC
Finished	2026-07-06 09:52:26 UTC
Duration	3m 38s

📊 Token Usage

Metric	Value
Input tokens	98,768
Cached input tokens	585,728
Output tokens	7,771
Total tokens	692,267
Invocations	1
Tool calls	33
Active time	3m 14s

Included usage estimate (subscription/local login): $1.02

🌿 Branch Info

Base: feature/CODUX-139-settings-mcp-and-custom-container
Head: task/feature-codux-139-settings-mcp-and-custom-contai-t01-codex-mr91ffpb

---

🤖 Generated by Code UX