Add SpeechTranscriber as STT option to Assist

[Copilot]

Summary

Adds opt-in local audio transcription using the SpeechTranscriber SPM package as an alternative to the assist websocket API for speech-to-text.

SPM Integration:

• Added bgoncal/SpeechTranscriber v1.0.0 as an Xcode SPM package dependency
• SpeechTranscriberAdapter wraps the SPM class, conforming to SpeechTranscriberProtocol for DI/testability
• The SPM package manages its own audio engine—no AudioRecorder or buffer forwarding needed for on-device STT

iOS 17+ Availability:

• Protocols (SpeechTranscriberProtocol, SpeechTranscriberDelegate) are in a separate SpeechTranscriberProtocol.swift file with no SPM import, available on all iOS versions
• SpeechTranscriberAdapter is gated with @available(iOS 17, *) since the SPM package requires iOS 17+
• NoOpSpeechTranscriber provides a fallback for pre-iOS 17 devices
• Construction site in AssistView+Build.swift uses #available(iOS 17, *) to conditionally select the implementation
• All new files are registered in the Xcode project (pbxproj) for proper compilation

Settings & Configuration:

• AssistConfiguration gains sttLanguage field (persisted in GRDB with auto-migration)
• AssistSettingsView adds on-device STT toggle + language picker from SFSpeechRecognizer.supportedLocales(), with unsupported-language warning
• Feature is off by default (opt-in)

AssistViewModel Flow:

• assistWithAudio() branches: on-device STT bypasses AudioRecorder entirely, server STT unchanged
• On transcription finish, text is sent via .text() source to the assist pipeline
• On failure, graceful fallback to server STT with info message in chat

// When on-device STT is enabled, audio capture is handled by the SPM package
if configuration.enableOnDeviceSTT {
    isRecording = true
    startOnDeviceTranscription() // SpeechTranscriberAdapter → SPM SpeechTranscriber
} else {
    audioRecorder.startRecording() // existing websocket STT path
}

Tests: 10 test cases covering enable/disable, language routing, text completion, empty input, failure fallback, and stop streaming.

Screenshots

Link to pull request in Documentation repository

Documentation: home-assistant/companion.home-assistant#

Any other notes

The adapter uses nonisolated protocol conformance with Task { @MainActor in } bridging to satisfy the SPM package's @MainActor requirement. Active tasks are tracked and cancelled to prevent race conditions on rapid start/stop.

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[bgoncal]

@copilot Build is failing, code needs to also be restricted to iOS17+ which is what SPM supports

[Copilot]

@copilot Build is failing, code needs to also be restricted to iOS17+ which is what SPM supports

Fixed in 0d69f31. Split the protocols into a separate SpeechTranscriberProtocol.swift (no SPM import, always available), gated SpeechTranscriberAdapter with @available(iOS 17, *), added NoOpSpeechTranscriber fallback for pre-iOS 17, and use #available(iOS 17, *) at the construction site in AssistView+Build.swift. Also registered all new files in the Xcode project (they were missing from the pbxproj which caused the "cannot find type" errors).