fix(tui): route Ctrl+B to voice toggle, not composer input

When the user runs /voice and then presses Ctrl+B in the TUI, three
handlers collaborate to consume the chord and none of them dispatch
voice.record:

- isAction() is platform-aware — on macOS it requires Cmd (meta/super),
  so Ctrl+B fails the match in useInputHandlers and never triggers
  voiceStart/voiceStop.
- TextInput's Ctrl+B pass-through list doesn't include 'b', so the
  keystroke falls through to the wordMod backward-word branch on Linux
  and to the printable-char insertion branch on macOS — the latter is
  exactly what timmie reported ("enters a b into the tui").
- /voice emits "voice: on" with no hint, so the user has no way to
  know Ctrl+B is the recording toggle.

Introduces isVoiceToggleKey(key, ch) in lib/platform.ts that matches
raw Ctrl+B on every platform (mirrors tips.py and config.yaml's
voice.record_key default) and additionally accepts Cmd+B on macOS so
existing muscle memory keeps working. Wires it into useInputHandlers,
adds Ctrl+B to TextInput's pass-through list so the global handler
actually receives the chord, and appends "press Ctrl+B to record" to
the /voice on message.

Empirically verified with hermes --tui: Ctrl+B no longer leaks 'b'
into the composer and now dispatches the voice.record RPC (the
downstream ImportError for hermes_cli.voice is a separate upstream
bug — follow-up patch).

ui-tui/src/__tests__/platform.test.ts

@@ -31,6 +31,36 @@ describe('platform action modifier', () => {
   })
 })
 
+describe('isVoiceToggleKey', () => {
+  it('matches raw Ctrl+B on macOS (doc-default across platforms)', async () => {
+    const { isVoiceToggleKey } = await importPlatform('darwin')
+
+    expect(isVoiceToggleKey({ ctrl: true, meta: false, super: false }, 'b')).toBe(true)
+    expect(isVoiceToggleKey({ ctrl: true, meta: false, super: false }, 'B')).toBe(true)
+  })
+
+  it('matches Cmd+B on macOS (preserve platform muscle memory)', async () => {
+    const { isVoiceToggleKey } = await importPlatform('darwin')
+
+    expect(isVoiceToggleKey({ ctrl: false, meta: true, super: false }, 'b')).toBe(true)
+    expect(isVoiceToggleKey({ ctrl: false, meta: false, super: true }, 'b')).toBe(true)
+  })
+
+  it('matches Ctrl+B on non-macOS platforms', async () => {
+    const { isVoiceToggleKey } = await importPlatform('linux')
+
+    expect(isVoiceToggleKey({ ctrl: true, meta: false, super: false }, 'b')).toBe(true)
+  })
+
+  it('does not match unmodified b or other Ctrl combos', async () => {
+    const { isVoiceToggleKey } = await importPlatform('darwin')
+
+    expect(isVoiceToggleKey({ ctrl: false, meta: false, super: false }, 'b')).toBe(false)
+    expect(isVoiceToggleKey({ ctrl: true, meta: false, super: false }, 'a')).toBe(false)
+    expect(isVoiceToggleKey({ ctrl: true, meta: false, super: false }, 'c')).toBe(false)
+  })
+})
+
 describe('isMacActionFallback', () => {
   it('routes raw Ctrl+K and Ctrl+W to readline kill-to-end / delete-word on macOS', async () => {
     const { isMacActionFallback } = await importPlatform('darwin')

ui-tui/src/app/slash/commands/session.ts

@@ -192,7 +192,7 @@ export const sessionCommands: SlashCommand[] = [
       ctx.gateway.rpc<VoiceToggleResponse>('voice.toggle', { action }).then(
         ctx.guarded<VoiceToggleResponse>(r => {
           ctx.voice.setVoiceEnabled(!!r.enabled)
-          ctx.transcript.sys(`voice: ${r.enabled ? 'on' : 'off'}`)
+          ctx.transcript.sys(`voice: ${r.enabled ? 'on — press Ctrl+B to record' : 'off'}`)
         })
       )
     }

ui-tui/src/app/useInputHandlers.ts

@@ -8,7 +8,7 @@ import type {
   SudoRespondResponse,
   VoiceRecordResponse
 } from '../gatewayTypes.js'
-import { isAction, isMac } from '../lib/platform.js'
+import { isAction, isMac, isVoiceToggleKey } from '../lib/platform.js'
 
 import { getInputSelection } from './inputSelectionStore.js'
 import type { InputHandlerContext, InputHandlerResult } from './interfaces.js'
@@ -370,7 +370,7 @@ export function useInputHandlers(ctx: InputHandlerContext): InputHandlerResult {
       return actions.newSession()
     }
 
-    if (isAction(key, ch, 'b')) {
+    if (isVoiceToggleKey(key, ch)) {
       return voice.recording ? voiceStop() : voiceStart()
     }
 

ui-tui/src/components/textInput.tsx

@@ -623,7 +623,19 @@ export function TextInput({
         return
       }
 
-      if ((k.ctrl && inp === 'c') || k.tab || (k.shift && k.tab) || k.pageUp || k.pageDown || k.escape) {
+      // Ctrl+B is the documented voice-recording toggle (see platform.ts →
+      // isVoiceToggleKey). Pass it through so the app-level handler in
+      // useInputHandlers receives it instead of being swallowed here as
+      // either backward-word nav (line below) or a literal 'b' insertion.
+      if (
+        (k.ctrl && inp === 'c') ||
+        (k.ctrl && inp === 'b') ||
+        k.tab ||
+        (k.shift && k.tab) ||
+        k.pageUp ||
+        k.pageDown ||
+        k.escape
+      ) {
         return
       }
 

ui-tui/src/lib/platform.ts

@@ -33,3 +33,17 @@ export const isMacActionFallback = (
 /** Match action-modifier + a single character (case-insensitive). */
 export const isAction = (key: { ctrl: boolean; meta: boolean; super?: boolean }, ch: string, target: string): boolean =>
   isActionMod(key) && ch.toLowerCase() === target
+
+/**
+ * Voice recording toggle key (Ctrl+B).
+ *
+ * Documented as "Ctrl+B" everywhere: tips.py, config.yaml's voice.record_key
+ * default, and the Python CLI prompt_toolkit handler. We accept raw Ctrl+B on
+ * every platform so the TUI matches those docs. On macOS we additionally
+ * accept Cmd+B (the platform action modifier) so existing macOS muscle memory
+ * keeps working.
+ */
+export const isVoiceToggleKey = (
+  key: { ctrl: boolean; meta: boolean; super?: boolean },
+  ch: string
+): boolean => (key.ctrl || isActionMod(key)) && ch.toLowerCase() === 'b'