refactor(decoders): per-instance cache replaces module lru_cache#42
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Move TypeAdapter / msgspec.json.Decoder caching from `@functools.lru_cache` module-level functions onto per-instance dicts on each decoder. No public API change; tied to decoder/client lifecycle; removes the autouse cache-clear test fixtures and the implicit cross-test pollution risk they were guarding against.
Three-task TDD sequence: PydanticDecoder per-instance _adapters dict, then MsgspecDecoder per-instance _msgspec_decoders dict, then the engineering.md Seam B description update.
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Summary
PydanticDecoder._adaptersandMsgspecDecoder._msgspec_decodersinstance dicts replace module-level@functools.lru_cachefactories. Cache lifetime now matches the decoder/client, not the process._clear_adapter_cache(test_decoders_pydantic.py) and_clear_msgspec_cache(test_decoders_msgspec.py, added one PR ago in PR feat!: multi-decoder routing (decoders=[...]) #41).No public API change. Folded into 0.9.0 (untagged).
Spec:
planning/specs/2026-06-10-decoder-instance-cache-design.mdPlan:
planning/plans/2026-06-10-decoder-instance-cache-plan.mdTest plan
just lintclean (ruff format + ruff check + ty)just testgreen — 485 passed, 100% coveragedecode()preserved; tests usepatch.object(PydanticDecoder, '_get_adapter', ...)andpatch.object(MsgspecDecoder, '_get_msgspec_decoder', ...)instead of patching module-level functionscan_decode_uses_cacheassertions shifted from_get_adapter.cache_info()to introspectingdecoder._adapters/decoder._msgspec_decodersdicts directlyMsgspecDecoder.can_decode'smsgspec.inspect.type_info+CustomTypefilter preserved verbatim (orthogonal to cache mechanics)planning/engineering.mdSeam B description updated to reflect per-instance ownership