Standalone override commands (/planmode, /model, /reasoning) discard unrelated chat prefs fields

[nathanschram]

Description

The standalone commands /planmode, /model, and /reasoning create EngineOverrides objects with only the fields they care about, discarding all other existing override fields. This means toggling one setting silently clears unrelated settings.

Reproduction

1. Open /config → toggle diff preview to ON → state shows diff_preview: true
2. Run /planmode auto (5 seconds later)
3. Check chat prefs state → diff_preview is now null

Confirmed via journalctl logs:

15:51:33 config.diff_preview.set chat_id=-5284581592 value=True
15:51:38 prefs.override.set chat_id=-5284581592 engine=claude model=None permission_mode=auto reasoning=None

The /planmode command at commands/planmode.py:68-72 created:

updated = EngineOverrides(
    model=current.model if current else None,
    reasoning=current.reasoning if current else None,
    permission_mode=mode,
)

This only preserved model and reasoning, discarding ask_questions, diff_preview, show_api_cost, and show_subscription_usage.

Affected commands (6 code paths)

Command	File	Lines	Fields preserved	Fields discarded
/planmode set	commands/planmode.py	68-72	model, reasoning	ask_questions, diff_preview, show_api_cost, show_subscription_usage
/planmode clear	commands/planmode.py	87-91	model, reasoning	ask_questions, diff_preview, show_api_cost, show_subscription_usage
/model set	commands/model.py	138-141	reasoning	permission_mode, ask_questions, diff_preview, show_api_cost, show_subscription_usage
/model clear	commands/model.py	213-216	reasoning	permission_mode, ask_questions, diff_preview, show_api_cost, show_subscription_usage
/reasoning set	commands/reasoning.py	156-158	model	permission_mode, ask_questions, diff_preview, show_api_cost, show_subscription_usage
/reasoning clear	commands/reasoning.py	236-238	model	permission_mode, ask_questions, diff_preview, show_api_cost, show_subscription_usage

Note: The /config sub-page handlers in config.py correctly preserve all fields — this bug was only in the standalone commands.

Impact

• Any setting toggled via /config (diff_preview, ask_questions, show_api_cost, show_subscription_usage) gets silently cleared when the user runs /planmode, /model, or /reasoning
• /model and /reasoning additionally discard permission_mode, so running /model set sonnet after /planmode on would clear plan mode
• Users have no indication their settings were lost
• This also caused the diff_preview gate in claude.py to appear broken — the gate code was correct but never saw diff_preview=True because /planmode had silently cleared it

Fix (applied on feature/github-hardening)

All 6 code paths now preserve all existing override fields when updating their own field. Example for /planmode:

updated = EngineOverrides(
    model=current.model if current else None,
    reasoning=current.reasoning if current else None,
    permission_mode=mode,
    ask_questions=current.ask_questions if current else None,
    diff_preview=current.diff_preview if current else None,
    show_api_cost=current.show_api_cost if current else None,
    show_subscription_usage=current.show_subscription_usage if current else None,
)

Also reverted temporary info-level debug logging in claude.py (diff_preview gate) back to debug level.

Tests

All 1563 tests pass (81% coverage). Existing tests for /config toggles, planmode, model, and reasoning commands all pass. Will verify end-to-end during staging dogfooding.