fix: preserve anthropic assistant ids in tool-first streams

[shaked-frame]

Summary

• add parentMessageId to Anthropic TOOL_CALL_START chunks so tool-first streams bind to the eventual assistant message id immediately
• add an Anthropic adapter regression covering tool-first streams and asserting the tool call chunk references the same assistant message id as TEXT_MESSAGE_START
• add a stream processor regression showing tool-first flows with parentMessageId preserve a single assistant message instead of creating a temporary local id

fixes #477

Verification

• pnpm exec vitest run packages/typescript/ai/tests/stream-processor.test.ts
• pnpm test:lib -- --runInBand in packages/typescript/ai
  • the new stream-processor regression passed
  • the package command still hits existing workspace resolution issues (@tanstack/ai-event-client, examples/ts-svelte-chat/.svelte-kit/tsconfig.json)
• pnpm test:lib -- --runInBand in packages/typescript/ai-anthropic
  • blocked by an existing @tanstack/ai package-entry resolution issue before the adapter test file runs

Summary by CodeRabbit

• Bug Fixes

  • Tool call events in streamed chats now include the parent message ID so tool calls correctly link to their originating message, improving tool-first and mixed streaming flows.

• Tests

  • Added tests covering tool-first flows and verifying message identity, ordering, and parent/child relationships.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 3fc3f0e4-ccfd-4d81-a5b8-d00c637e6003

📥 Commits

Reviewing files that changed from the base of the PR and between 4884561 and f07aad7.

📒 Files selected for processing (1)

• packages/typescript/ai-anthropic/src/adapters/text.ts

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📝 Walkthrough

Walkthrough

Anthropic text adapter now includes parentMessageId (the originating messageId) on emitted TOOL_CALL_START events in tool-first streaming flows; two new tests validate emission and downstream preservation of that server-provided message id.

Changes

Cohort / File(s)	Summary
Anthropic Text Adapter packages/typescript/ai-anthropic/src/adapters/text.ts	Adds parentMessageId: messageId to TOOL_CALL_START payload in both places that emit that event (first input_json_delta during streaming tool_use, and content_block_stop when tool_use ends without streaming args).
Anthropic Adapter Tests packages/typescript/ai-anthropic/tests/anthropic-adapter.test.ts	New stream-processing test that mocks a tool-first Anthropic response and asserts the emitted TOOL_CALL_START chunk contains parentMessageId matching the TEXT_MESSAGE_START messageId.
Stream Processor Tests packages/typescript/ai/tests/stream-processor.test.ts	New test ensuring when TOOL_CALL_START includes parentMessageId, the resulting assistant UIMessage preserves that server-provided id and that message parts (tool-call then text) are ordered and populated correctly.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐇 I hop through streams with careful cheer,
I carry IDs so messages stay near.
Tools leap first, then text follows through,
One stable id keeps the parts true. 🥕

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	Title clearly summarizes the main change: adding parentMessageId preservation in Anthropic tool-first streams to stabilize assistant message IDs.
Description check	✅ Passed	Description covers key changes with summary, verification steps, and issue reference, but lacks detailed checklist completion and changeset confirmation.
Linked Issues check	✅ Passed	Code changes fully address issue #477: parentMessageId is added to TOOL_CALL_START events, with tests verifying tool-first streams preserve a single assistant message ID.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the linked issue: adapter changes emit parentMessageId, and test regressions validate the fix. No unrelated modifications present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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