[L-06] Add a graceful Usage Dock quit request

[Arrangedgodly]

Behavior

Usage Dock recognizes the exact sole argument --quit-from-launchpad. If an instance is already open, the single-instance callback exits it. If no instance is open, the flagged invocation exits during setup before tray services start. This gives Launchpad a local graceful quit path without adding an HTTP shutdown endpoint.

Verification

• cargo fmt --all --check — passed.
• cargo test --manifest-path apps/desktop-tauri/src-tauri/Cargo.toml --bin codexbar-desktop-tauri launchpad_quit -- --nocapture — 2 passed.

The installed app needs a build containing this change. A Windows app session was not launched for runtime testing.

Summary by CodeRabbit

• New Features
  • The desktop app now exits immediately when launched with the dedicated quit request as its only argument. This also applies when the request is sent to an already-running instance, allowing the app to close without following its usual launch or reopen behavior. Other argument combinations continue to use the existing behavior.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 21b5b90c-006e-4562-af5e-f8c24a904338

📥 Commits

Reviewing files that changed from the base of the PR and between b585d48 and 321377e.

📒 Files selected for processing (1)

• apps/desktop-tauri/src-tauri/src/main.rs

Included review availability: This review used your included allowance. Your plan provides up to 4 included reviews per hour; 3 remain after this review.

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📝 Walkthrough

Walkthrough

The desktop process now recognizes --quit-from-launchpad only when it is the sole argument. Matching initial and single-instance launches exit with status 0. Other argument forms continue through existing launch and reopen behavior.

Changes

Launchpad quit handling

Layer / File(s)	Summary
Recognize and handle Launchpad quit requests apps/desktop-tauri/src-tauri/src/main.rs	A helper matches only the exact sole quit argument. Initial launches exit before normal setup, and matching single-instance invocations exit before the primary-window reopen check. Tests cover accepted and rejected argument forms.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature

Suggested reviewers: finesssee

Merge Risk: ⚪ Minimal · up to 32137

The Launchpad quit flag exits an existing Usage Dock instance or prevents a new invocation from completing startup. No actionable merge risk remains; the change is ready for normal checks.

Architecture Summary

Architecture risk: 🔵 Low · up to 32137

The change affects 1 system.

Changed systems: apps/desktop-tauri

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — apps/desktop-tauri (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in apps/desktop-tauri/src-tauri/src/main.rs: Adds is_launchpad_quit_request, which returns true only when the first argument is exactly --quit-from-launchpad and no additional arguments follow.
• observed — Modified behavior in apps/desktop-tauri/src-tauri/src/main.rs: The initial process arguments are checked for the Launchpad quit request and the result is retained for setup.
• observed — Modified behavior in apps/desktop-tauri/src-tauri/src/main.rs: The single-instance callback now exits with status 0 and returns immediately for an exact sole Launchpad quit argument; other invocations continue to the existing primary-window reopen check.
• observed — Modified behavior in apps/desktop-tauri/src-tauri/src/main.rs: Setup exits with status 0 before normal setup tasks when the initial process arguments matched the Launchpad quit request.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding a graceful quit request from the Usage Dock/Launchpad.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

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