fix: race conditions

[joshribakoff]

Before Submitting This PR

Please confirm you have done the following:

• I have searched existing issues and pull requests (including closed ones) to ensure this isn't a duplicate
• I have read CONTRIBUTING.md

Human Written Description

Implements state machine, single source of truth, declarative UI pattern, testing pattern, fixes race conditions at multiple layers. Trades off concurrency for simplicity, laying the foundation for future extensibility (and concurrency). Replaces jQuery style imperative UI management with React style declarative updates.

I am new to Rust and tried to do my best with AI, open to feedback / feel free to close and "steal" the idea but I would love feedback and/or credit!

Related Issues/Discussions

Fixes #641, #462

How to Reproduce

Three ways to trigger / different issue(s):

1. During transcription: Record something, release hotkey, then while transcribing trigger the hotkey again., global lock solves it
2. Rapid toggle: Quickly press and release the hotkey multiple times in succession capturing small empty audio packets rapidly, causes "deadlock" (not responding), global lock solves it.
3. Hold and spam: Hold down the hotkey key rapidly (same as 2) but UI panel disappears but audio cues indicates its still recording (which it is). Global lock does not solve it, required declarative UI.

Testing

Tested locally by triggering all three reproduction scenarios above.

AI Assistance

• AI was used (please describe below)

If AI was used:

• Tools used: Claude Code
• How extensively: Pair programming to implement the global lock and declarative UI sync

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The app has multiple sources of state that can get out of sync - different mutex locks at different layers, imperative UI updates with delays that don't get cancelled. This PR demonstrates a pattern that fixes the UI overlay and tray icon: a single source of truth state machine where UI syncs declaratively when the phase changes (similar to React's model).

This also fixes the "Not Responding" freeze by adding a global lock that prevents concurrent operations.

Intentionally pragmatic: I've kept this PR minimal to avoid overwhelming reviewers with huge changes. It focuses on fixing the immediate issue and demonstrating a pattern that could be extended to other parts of the app in future PRs.

Other state could be consolidated into this pattern in follow-up PRs:

• Audio feedback timing (stop playing one sound, play the latest sound instead, etc)
• The functionality that mutes the sound on the users system also feels like declarative "UI" state, but is out of scope for this PR too.

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In “Rust way” terms: I made state transitions explicit, serialized with a single lock, and made UI a pure projection of state.
That’s consistent with correctness-first design.

I’d pitch it as:

• The previous decentralized approach lacked a single source of truth for phase, which caused races.
• The controller is a minimal, scoped state machine with clear transitions.
• If we want “Rustier” later, we can evolve it into a channel-driven state machine without changing call sites (hopefully with tests and mock services, or something).

[cjpais]

Thanks for this, this is one of the higher priority issues for me. Will try and review in about a week