fix(key_codes): add Function key arm so macOS fn can be bound to a chord

[sridhar-3009]

Fixes #941.

Problem

key_from_str() in tauri/src-tauri/src/key_codes.rs had no arm for "Function", so it fell through to None. build_chord propagates that None as a hard Err via ?, so any chord containing fn made build_chord_bindings fail entirely — HotkeyMonitor was never spawned, silently disabling both push-to-talk and toggle-to-talk until the chord was changed back to a mapped key. No error is logged either, since the failure happens before the "ChordMatcher build failed" log line would run.

Every other layer already supports it:

• keytap::Key::Function exists (confirmed in jamiepine/keytap's src/key.rs)
• keytap's macOS key tap already observes it (kVK_Function → Key::Function)
• the frontend's canonicalKeyFromEvent/displayLabelForKey already allowlist/label 'Function' → 'fn'

Only this string→Key bridge was missing the arm.

Fix

One arm, exactly as suggested in the issue:

"Function" => Key::Function,

Testing

There's no existing test suite for key_codes.rs (no #[test] module in the file), so I didn't add test scaffolding beyond the scope of this one-line fix. I don't have a Mac to verify the chord end-to-end, but the fix is a direct, mechanical addition matching the pattern of every other key arm in the same match block.

Summary by CodeRabbit

• Bug Fixes
  • Improved keyboard shortcut handling by recognizing the canonical “Function” key name when restoring saved key combinations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: e2ce18af-50c8-44f5-8fd4-d462f07eb18b

📥 Commits

Reviewing files that changed from the base of the PR and between 52f8d8d and 2b8cd19.

📒 Files selected for processing (1)

• tauri/src-tauri/src/key_codes.rs

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📝 Walkthrough

Walkthrough

Changes

Function key support

Layer / File(s)	Summary
Function key string mapping tauri/src-tauri/src/key_codes.rs	key_from_str now maps "Function" to keytap::Key::Function for chord persistence and reconstruction.

Estimated code review effort: 1 (Trivial) | ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the key change: adding Function key support for macOS chord binding.
Linked Issues check	✅ Passed	The change restores the missing Function-to-Key mapping required to let macOS fn chords build successfully.
Out of Scope Changes check	✅ Passed	The PR is narrowly scoped to the missing Function key arm and introduces no unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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