Global key listener

Electron's globalShortcutcan't express hold-to-talk or reliably block a key from the focused app. VoiceFlow instead spawns a small Rust binary that uses rdev's grab API to intercept the macOS event stream, giving it press/release granularity and the ability to swallow matched keys.

The main process's shortcut-manager talks to the binary with newline-delimited JSON. It writes a register_hotkeys command listing the key combinations to watch; the binary streams back key events and periodic heartbeats.

{ "command": "register_hotkeys",
  "hotkeys": [ { "keys": ["ShiftLeft", "Space"] },
               { "keys": ["BackQuote"] } ] }

{ "type": "keydown", "key": "Space", "timestamp": "..." }
{ "type": "keyup",   "key": "Space", "timestamp": "..." }
{ "type": "heartbeat_ping", "id": "7", "timestamp": "..." }

The binary tracks the set of currently-pressed keys. On each press it checks whether the pressed set exactly equals any registered combo; if so, it returns None from the grab callback, which blocks the key from reaching other apps. The main process independently tracks pressed tokens to decide when to start and stop recording.

• Shortcuts are expanded into raw key variants so left/right modifiers both match.
• A special case blocks the Fn key (reported as Unknown(179)) when an Fn shortcut is registered.
• Matching requires an exact set — extra held keys mean no match, keeping toggle and hold from overlapping.

A key listener that dies or gets stuck would silently break every shortcut, so the manager supervises it aggressively.

In development the manager runs the Cargo build output for your architecture (e.g. aarch64-apple-darwin). In a packaged build it's bundled as an extra resource under resources/binaries. See Build & releasefor how it's compiled and packaged.