Three tightenings on the surface introduced in the round-1 fix:
* **``/voice tts`` reset custom bindings to Ctrl+B.** The ``tts`` branch
of ``voice.toggle`` omitted ``record_key`` from its response, so the
frontend's ``r.record_key ?? 'ctrl+b'`` coerced a user's custom
binding back to the default on every TTS toggle. Two-sided fix:
the backend now includes ``record_key`` on the ``tts`` branch (parity
with ``status``/``on``/``off``), and the slash handler only pushes
frontend state when the response actually carries ``record_key`` —
belt-and-suspenders against any future branch forgetting to include
it.
* **``super+b`` / ``win+b`` / ``cmd+b`` displayed "Cmd+B" on Linux and
Windows.** ``formatVoiceRecordKey`` rendered ``mod === 'super'`` as
``Cmd`` universally, which told non-mac users the wrong modifier to
press even though ``isVoiceToggleKey`` matched the right event bits.
Gate the label to ``isMac`` so non-mac renders ``Super+B``.
* **``control+b`` / ``ctrl + b`` lost the macOS Cmd+B fallback.**
``_isDefaultVoiceKey`` keyed off ``parsed.raw`` — so
semantically-equal aliases of the documented default dropped into
the strict branch even though they bind Ctrl+B. Compare on the
parsed spec (mod + ch + named) instead.
Coverage added: Linux ``Super+B`` rendering (and macOS ``Cmd+B``),
``control+b`` / ``ctrl + b`` accepting the Cmd+B fallback on darwin,
``/voice tts`` without ``record_key`` not clobbering cached binding,
and a backend regression asserting every ``voice.toggle`` branch
carries the configured key.
Suite: 579/579 TUI vitest green, 2/2 backend voice tests green,
tsc --noEmit clean.