Add native tokenCount method to LanguageModelSession#12
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- Expose SystemLanguageModel.tokenCount(for:) via Nitro bridge (iOS 26.4+) - Add tokenCountError case to AppleAIErrors - Reject with UNSUPPORTED_PLATFORM on iOS < 26.4
- Expose SystemLanguageModel.contextSize (iOS 26.4+) via Nitro spec - Replace hardcoded 4096 context size with native value - Update example app to use session.tokenCount() with estimation fallback - Add `estimated` flag to TokenMetrics
- Add API reference for tokenCount() and wasContextReset - Update contextSize docs to reflect native bridging on iOS 26.4+ - Clarify contextSize returns undefined on iOS 26.0–26.3
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Summary
Bridges Apple's
SystemLanguageModeltoken and context APIs (iOS 26.4+), replaces the previously hardcoded 4,096-token estimate, and surfaces automatic context-reset signaling.Native APIs
LanguageModelSession.tokenCount(prompt)— returns the token count for a given string usingSystemLanguageModel.tokenCount(for:). Rejects withUNSUPPORTED_PLATFORMon iOS < 26.4.LanguageModelSessionFactory.contextSize— exposesSystemLanguageModel.contextSizeas a read-only property.getFoundationModelsContextSize()/FoundationModelsAvailability.contextSizenow return the native value on iOS 26.4+ andundefinedon 26.0–26.3 (previously always4096).LanguageModelSession.wasContextReset— readonly getter indicating whether the session's context was automatically summarized/reset after hitting the model's limit.TOKEN_COUNT_ERRORerror case and regenerates the Nitro bridge (C++/Swift) for the new method and property.Example app
example/utils/tokenMetrics.tsnow callssession.tokenCount()when available and falls back to character-based estimation on older iOS, flagged via a newestimated: booleanfield onTokenMetrics.getTokenMetricsand await the result, and displaywasContextResetto the user when a summarization occurs.Docs
tokenCount()andwasContextReset.getFoundationModelsContextSize()/availability.contextSizenotes updated to describe native bridging on iOS 26.4+ andundefinedon older versions.Testing
tokenCountresolves with a valid count on iOS 26.4+ device/simulator.tokenCountrejects withUNSUPPORTED_PLATFORMon iOS 26.0–26.3.getFoundationModelsContextSize()returns a number on 26.4+ andundefinedon earlier versions.estimatedflag flips correctly.wasContextResetand confirm the UI surfaces it.