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

  • Ensure tool call events in streamed chats include the parent message ID so tool calls correctly link to their originating message.
  • Improve handling of tool-first streaming flows where tool data arrives before text content.

• 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: a878a9c9-5acc-4ea7-aae7-e748dddd919e

📥 Commits

Reviewing files that changed from the base of the PR and between dc23cbf and 4884561.

📒 Files selected for processing (1)

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

🚧 Files skipped from review as they are similar to previous changes (1)

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

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📝 Walkthrough

Walkthrough

Anthropic adapter now attaches parentMessageId (the originating messageId) to emitted TOOL_CALL_START events in tool-first streaming flows; two new tests verify that adapter emission and downstream stream processing preserve and use this server-provided message id.

Changes

Cohort / File(s)	Summary
Anthropic Text Adapter packages/typescript/ai-anthropic/src/adapters/text.ts	Adds parentMessageId: messageId to the TOOL_CALL_START event payload in two code paths: on first input_json_delta for streaming tool_use, and on content_block_stop when a tool_use block ends before args streaming begins.
Anthropic Adapter Tests packages/typescript/ai-anthropic/tests/anthropic-adapter.test.ts	New stream-processing test mocking a tool-first Anthropic response; asserts the emitted TOOL_CALL_START chunk contains parentMessageId equal to the TEXT_MESSAGE_START messageId.
Stream Processor Tests packages/typescript/ai/tests/stream-processor.test.ts	New test ensures that when TOOL_CALL_START includes parentMessageId, the resulting assistant UIMessage uses that server-provided id and that parts are ordered and populated correctly (tool-call then text).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐇 I hop through streams where messages start,
I stitch IDs so no parts drift apart,
Tools jump first, then text will flow,
Parent IDs keep the message whole — hooray, let's go! 🥕

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Description check	❓ Inconclusive	The description includes clear summary of changes and references the linked issue (#477), but is missing the required 🎯 Changes section structure and checklist items from the template.	Complete the PR description using the provided template: add structured 🎯 Changes section, check off the checklist items, and confirm changeset generation for release impact.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: adding parentMessageId preservation to Anthropic tool-first streams, which directly addresses the linked issue about message id instability.
Linked Issues check	✅ Passed	The code changes directly address issue #477 by adding parentMessageId to TOOL_CALL_START chunks, enabling tool-first streams to bind to the eventual assistant message id, and include regression tests validating the fix.
Out of Scope Changes check	✅ Passed	All changes are focused and scoped: modifications to the Anthropic adapter to emit parentMessageId, plus two targeted regression tests validating the fix—no extraneous changes detected.
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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