fix: preserve providerMetadata on reasoning chunks in applyChunkToParts#1301
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threepointone merged 2 commits intomainfrom Apr 13, 2026
Merged
fix: preserve providerMetadata on reasoning chunks in applyChunkToParts#1301threepointone merged 2 commits intomainfrom
threepointone merged 2 commits intomainfrom
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The reasoning-end and reasoning-delta handlers in message-builder.ts were not copying chunk.providerMetadata onto the persisted reasoning part. For Anthropic models with extended thinking, the signature arrives on reasoning-end.providerMetadata — dropping it means subsequent turns cannot round-trip the thinking block, silently breaking multi-turn extended thinking. Both handlers now merge chunk.providerMetadata onto the part, matching the behavior of source and tool chunk handlers. Fixes #1299. Made-with: Cursor
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Summary
applyChunkToPartsinmessage-builder.tswas silently droppingchunk.providerMetadataonreasoning-endandreasoning-deltachunks. For Anthropic models with extended/adaptive thinking, the thinking block signature arrives onreasoning-end.providerMetadata.anthropic.signature— without it,@ai-sdk/anthropiccannot reconstruct the thinking block on subsequent turns and silently drops it, making extended thinking effectively single-turn.chunk.providerMetadataonto the persisted part via a newmergeProviderMetadatahelper, matching the behavior of source and tool chunk handlers in the same file.reasoning-end, metadata onreasoning-delta, merge across delta+end, no-op when metadata is absent, and fallback part creation with metadata.Fixes #1299.
Test plan
npx nx run agents:test:workers)stream-accumulator.test.tscover the fixMade with Cursor