[Bug]: Data race in debug key capture (DebugKeysCommand.CaptureSequence)

[ben-ranford]

Bug Description

Concurrent calls to DebugKeysCommand.CaptureSequence() can race on dkc.sequences appends/writes, causing non-deterministic behaviour and race detector failures.

Steps to Reproduce

Steps to reproduce the behaviour:

1. Check out branch main before PR [bug] debug-keys-capture-sequence-race #341.
2. Run command go test -race ./internal/keybindings -run TestDebugKeysCommand_ConcurrentAccess -count=1.
3. See WARNING: DATA RACE with stack traces pointing to CaptureSequence() in internal/keybindings/parser.go.

Expected Behavior

Concurrent key capture should be thread-safe and deterministic, with no race detector warnings.

Screenshots

N/A

Environment

• OS: Darwin 25.2.0
• Go Version: go1.25.7 darwin/arm64
• ggc Version: v7 (source build)
• git Version (run git --version): git version 2.39.5 (Apple Git-154)

Additional Context

• Root cause: shared mutable fields (capturing, sequences) were read/written across StartCapture, CaptureSequence, StopCapture, and IsCapturing without synchronisation.
• Fix is in PR [bug] debug-keys-capture-sequence-race #341, which adds mutex protection, snapshots sequences in StopCapture(), and updates save/read paths accordingly.
• Validation after fix:
  • go test -race ./internal/keybindings -run TestDebugKeysCommand_ConcurrentAccess -count=1
  • go test ./internal/keybindings