perf(asr): speed up local Flow dictation and land CLM/keyboard refactor
Reduce perceived latency from key release to final text: - Adaptive chunking: 2.5s first chunk + 5s follow-ups so short utterances start on-device recognition while still recording. - Session-level ASR warmup and audio-format cache reuse to remove per-utterance cold-start of SpeechAnalyzer. - Mirror live pipelined partials to the keyboard transcript line via a new flow.transcriptionPartial App Group key + Darwin ping. Also commits the accumulated custom language model, Flow session, keyboard extension restructure, and Xiaomi MiMo provider work in progress on this branch.
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@@ -47,6 +47,9 @@ public protocol ASRService: Sendable {
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/// Clears cancellation / cached session state before a new utterance.
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func resetForNewUtterance()
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/// Pre-load locale assets and analyzer format for lower first-chunk latency.
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func warmup(locale: Locale) async
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/// Transcribe one PCM chunk (Flow pipelined path). Default wraps `transcribe(stream:)`.
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func transcribeChunk(samples: [Float], locale: Locale) async -> ASRChunkResult
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}
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@@ -60,6 +63,8 @@ public enum ASRChunkResult: Sendable, Equatable {
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extension ASRService {
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public func resetForNewUtterance() {}
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public func warmup(locale: Locale) async {}
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public func transcribeChunk(samples: [Float], locale: Locale) async -> ASRChunkResult {
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guard !samples.isEmpty else { return .success("") }
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if Task.isCancelled { return .cancelled }
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@@ -116,27 +121,7 @@ public enum ASREvent: Sendable, Equatable {
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// MARK: - Factory
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public enum ASRServiceFactory {
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/// Returns the on-device ASR backend. As of v0.2.0 the only
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/// supported `LocalASRBackend` is iOS 26 `SpeechAnalyzer` +
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/// `DictationTranscriber` (always on-device, no asset download),
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/// so the factory collapses to a single concrete type. We keep the
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/// `localBackend` parameter on the signature so the next non-iOS
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/// backend can slot in without touching every call site.
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///
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/// The cloud engine also routes through `SpeechAnalyzerASR`: the
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/// user expectation is that ASR is the local half of the pipeline
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/// regardless of where the LLM polish happens.
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public static func make(
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engineMode: String,
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localBackend: LocalASRBackend = .speechAnalyzer
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) -> ASRService {
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SpeechAnalyzerASR()
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}
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/// Back-compat overload for callers that only ever want the
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/// SpeechAnalyzer path. The previous single-backend build used
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/// this signature; new code should pass the engine mode explicitly
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/// so any future non-iOS backend is honoured.
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/// Returns the on-device `SpeechAnalyzer` + `DictationTranscriber` backend.
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public static func make() -> ASRService {
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SpeechAnalyzerASR()
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}
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@@ -197,12 +182,52 @@ final class SpeechAnalyzerASR: ASRService, @unchecked Sendable {
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private var chunkAnalyzerFormat: AVAudioFormat?
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func resetForNewUtterance() {
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// Keep chunk format / asset cache warm across utterances in one Flow session.
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}
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func invalidateChunkPreparationCache() {
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lock.withLock {
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chunkPreparedLocaleID = nil
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chunkAnalyzerFormat = nil
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}
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}
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func warmup(locale: Locale) async {
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guard let resolvedLocale = await DictationTranscriber.supportedLocale(equivalentTo: locale) else {
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return
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}
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let localeID = resolvedLocale.identifier(.bcp47)
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let cachedLocaleID = lock.withLock { chunkPreparedLocaleID }
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if cachedLocaleID == localeID, lock.withLock({ chunkAnalyzerFormat != nil }) {
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return
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}
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let lmConfiguration = CustomLanguageModelManager.shared.configurationForTranscription(
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locale: resolvedLocale
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)
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let transcriber = CustomLanguageModelManager.makeDictationTranscriber(
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locale: resolvedLocale,
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lmConfiguration: lmConfiguration
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)
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do {
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try await Self.prepareAssetsIfNeeded(for: transcriber, locale: resolvedLocale)
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guard let format = await SpeechAnalyzer.bestAvailableAudioFormat(
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compatibleWith: [transcriber],
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considering: Self.captureFormat
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) else {
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return
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}
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lock.withLock {
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chunkPreparedLocaleID = localeID
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chunkAnalyzerFormat = format
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}
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Self.debug("warmup ready locale=\(localeID)")
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} catch {
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Self.debug("warmup failed: \(error.localizedDescription)")
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}
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}
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func transcribeChunk(samples: [Float], locale: Locale) async -> ASRChunkResult {
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guard !samples.isEmpty else { return .success("") }
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if Task.isCancelled { return .cancelled }
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@@ -228,9 +253,12 @@ final class SpeechAnalyzerASR: ASRService, @unchecked Sendable {
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throw ASRChunkError.localeUnsupported
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}
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let localeID = resolvedLocale.identifier(.bcp47)
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let transcriber = DictationTranscriber(
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let lmConfiguration = CustomLanguageModelManager.shared.configurationForTranscription(
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locale: resolvedLocale
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)
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let transcriber = CustomLanguageModelManager.makeDictationTranscriber(
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locale: resolvedLocale,
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preset: .progressiveLongDictation
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lmConfiguration: lmConfiguration
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)
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let analyzerFormat: AVAudioFormat
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@@ -337,9 +365,12 @@ final class SpeechAnalyzerASR: ASRService, @unchecked Sendable {
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}
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// Each pipelined chunk is ≤ 30 s; long dictation preset keeps a
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// single chunk coherent (Flow utterances run up to 3 min).
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let transcriber = DictationTranscriber(
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let lmConfiguration = CustomLanguageModelManager.shared.configurationForTranscription(
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locale: resolvedLocale
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)
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let transcriber = CustomLanguageModelManager.makeDictationTranscriber(
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locale: resolvedLocale,
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preset: .progressiveLongDictation
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lmConfiguration: lmConfiguration
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)
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do {
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try await Self.prepareAssetsIfNeeded(for: transcriber, locale: resolvedLocale)
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