[Bug]: @ file/folder picker shows no matching files or folders even with an open project

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. Open T3 Code nightly with a project/workspace loaded
2. In the composer, type @ to trigger the file/folder mention picker
3. Result: "No matching files or folders." appears immediately, even when the project has hundreds of files

Expected behavior

Typing @ should list the project files/folders for mention, matching what the composer placeholder promises ("@tag files/folders").

Actual behavior

The @ picker always shows "No matching files or folders." regardless of project size. Only $ (skills) and / (commands) work. Since the composer placeholder advertises @tag files/folders.

Impact

Blocks work completely

Version or commit

0.0.34-nightly.20260819.1133 (latest nightly)

Environment

macOS on Apple Silicon M4 Pro, T3 Code nightly 0.0.34-nightly.20260819.1133, Codex provider

Logs or stack traces

Screenshots, recordings, or supporting files

No response

Workaround

No workaround yet. Typing the full file path in plain text works as a mention substitute.

Start in apps/web and reproduce the issue in T3 Code nightly with a loaded project, then inspect the composer’s @ file/folder mention picker. Trace why it immediately shows "No matching files or folders" while $ skills and / commands work; done means @ lists matching project files and folders as promised by the composer placeholder.