Add constrained generation protocol and pipelined strategy (3/4) - #146
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stikves merged 5 commits intoAug 14, 2026
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…rategy Introduce the abstraction layer for GPU-accelerated grammar-constrained decoding, independent of the engine implementation: - ConstrainedGenerationCapable: protocol for engines that support GPU-side bitmask application during sampling - ConstrainedSessionHandle: thread-safe wrapper around ConstrainedGenerationSession with checkout/checkin cache pattern - PipelinedConstrainedDecodingStrategy: AsyncSequence-based strategy that drives constrained token generation through a capable engine - Integration tests with MockConstrainedEngine covering session lifecycle, cache reuse, stop sequences, and error paths
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Nice work, please consider comments before merging
- ConstrainedSessionHandle: clarify it is single-owner, not thread-safe - Remove misleading warning about multi-token stops (handled by iterator) - Add consecutive decode-failure guard (maxConsecutiveDecodeFailures=10) - Document conformer obligations on ConstrainedGenerationCapable protocol - Note that AsyncThrowingStream.AsyncIterator copy is safe (class-backed)
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Summary
Introduces the abstraction layer for GPU-accelerated grammar-constrained decoding, split out from #114 for independent review:
ConstrainedGenerationCapableprotocol: capability signal for engines that support GPU-side bitmask application during samplingConstrainedSessionHandle: thread-safe wrapper aroundConstrainedGenerationSessionwith checkout/checkin cache pattern for reuse across callsPipelinedConstrainedDecodingStrategy:AsyncSequence-based strategy that drives constrained token generation through a capable engine, with single-use iteration guardMockConstrainedEnginecovering session lifecycle, cache reuse, schema invalidation, stop sequences, and error pathsThis PR contains no engine implementation — a follow-up PR (4/4) will add the
CoreAIPipelinedEngineconformance and CLI wiring.Dependencies
Builds on top of:
Test plan
xcodebuild build-for-testing -scheme CoreAILMpassesPipelinedConstrainedIntegrationTestssuite passes (mock-only, no GPU required)