Cursor-style Debug composer mode

Composer Debug is ACE’s Cursor-like debug loop: investigate with live session context, then Review & Apply a minimal fix. It is not silent Agent auto-apply, and it is not Ask-only.

What it does

1. Selecting Debug focuses the Debug sidebar and status tip.
2. AI requests attach context.debug_session when available:
   • console_tail, stack, paused_file / paused_line
   • breakpoints, variables, runtime, target_path
3. Server prompt (COMPOSER MODE: DEBUG) asks for hypotheses → root cause → minimal edits.
4. File tools allowed: read + single-file edits (edit_file, propose_edit, write_full_file, create_file). No create_multiple_files.
5. Client: Review & Apply enabled; auto-apply skipped in Debug.
6. Large scaffolds (“full ecommerce app”, “from scratch”) → switch-to-Agent CTA.

Ask ACE wiring

Manual test checklist

Use desktop-ide/samples/phase3-run-debug/ (debug-me.js, fail-on-purpose.js, hello.js).

1. Composer → Debug → Debug sidebar opens; tip mentions Review & Apply.
2. Open debug-me.js, set a breakpoint, Start, hit pause → Ask in Debug about the bug → reply uses console/pause context.
3. Open fail-on-purpose.js, Debug Start (or Run) until error → Ask ACE → mode stays Debug → Review card for a small fix → Apply → re-run.
4. Open hello.js, Run to exit 0 → Ask ACE → Ask mode, no disk writes.
5. In Debug, prompt “build a full ecommerce app from scratch” → Agent switch CTA (no scaffold actions).
6. Confirm Agent still auto-applies when that setting is on; Debug never auto-applies.

Related docs

• ask-vs-agent.md — mode gate table
• run-debug.md — Run/Debug panels + F5