feat(ai-claude-code): stream tool-call arguments (+ fix processor id-rename orphaning tool results)

[ozolcar]

What

Two related changes, surfaced while wiring structured output through a tool call on the @tanstack/ai-claude-code harness adapter.

1. @tanstack/ai-claude-code: stream tool-call arguments (feat, patch)

The stream translator only forwarded text_delta and thinking_delta partial events, so a tool_use block surfaced as a single completed TOOL_CALL_START/ARGS/END at the end of the message. It now also translates the SDK's partial tool input (content_block_start for tool_use into TOOL_CALL_START, input_json_delta into incremental TOOL_CALL_ARGS, content_block_stop into TOOL_CALL_END), matching how the @tanstack/ai-anthropic and @tanstack/ai-openai adapters already stream tool args. The complete assistant message dedupes anything already streamed via partials (tracked by tool-call id, mirroring the existing text/thinking message-id dedup). With streamPartials: false, tool calls still emit whole from the complete message.

This lets structured output routed through a tool call paint incrementally as the model writes it, instead of arriving all at once at run end.

Also in this commit:

• The partial TOOL_CALL_START carries parentMessageId (mirroring the partial text path and every other adapter), so a tool-first stream groups the call under the correct message.
• On abort mid-tool-args, the catch flushes the in-flight partial tool call (mirroring handleResult) so its TOOL_CALL_START is still paired with a TOOL_CALL_END and an interrupted TOOL_CALL_RESULT, upholding the module's documented invariant.

2. @tanstack/ai: atomic message-id rename (fix, patch)

Independently reachable from any adapter that omits parentMessageId (optional per the AG-UI spec; Mistral omits it today). When a tool call streams before any text, the StreamProcessor creates a placeholder assistant message and renames it to the real provider id on TEXT_MESSAGE_START. That rename updated messages, messageStates, and activeMessageIds but not toolCallToMessage, structuredMessageIds, or structuredOutputUpdateBatches, so a TOOL_CALL_RESULT arriving after the rename resolved to the vanished placeholder id and was silently dropped. The rename now goes through a single renameMessageId() seam that remaps every id-keyed structure (the same set already enumerated by pruneToMessages() and reset()). Complements the adapter-side fix in #480.

Why

Routing structured output through a tool call is the sanctioned way to stream it on this harness (native structured_output only appears in the final result, not as deltas). Getting there surfaced (1) the translator dropping input_json_delta, and (2) the processor's rename orphaning a tool result when parentMessageId is absent.

Test plan

• @tanstack/ai-claude-code: new translate tests covering partial tool-arg streaming plus dedup, abort mid-tool-args pairing an interrupted result, parentMessageId grouping, sequential tool blocks, and zero-arg START/END. 6 files, 39 tests pass.
• @tanstack/ai: new stream-processor regression test (tool-first without parentMessageId, then rename, then the tool result attaches, which was silently dropped); the existing provided-parentMessageId test still passes because renameMessageId no-ops when ids match. 63 files, 1133 tests pass.
• Both: test:types, test:eslint (0 errors), build clean.
• Two changesets (@tanstack/ai-claude-code patch, @tanstack/ai patch).

Closes #901.

Summary by CodeRabbit

• New Features

  • Tool calls can now stream arguments incrementally as they arrive, instead of waiting until the end.
  • Claude tool-use streams are handled more smoothly, including cases where tools start before text.

• Bug Fixes

  • Fixed a case where tool results could be lost when a temporary message was replaced by the final one.
  • Improved handling for interrupted tool calls so partial activity still closes cleanly.

• Tests

  • Added coverage for incremental tool-call streaming, deduplication, message grouping, and interrupted streams.

[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: 654e77aa-ee65-4e8d-9221-c2ece217ba19

📥 Commits

Reviewing files that changed from the base of the PR and between e3de949 and 984a601.

📒 Files selected for processing (7)

• .changeset/processor-message-id-rename.md
• .changeset/stream-tool-call-args.md
• packages/ai-claude-code/src/stream/sdk-types.ts
• packages/ai-claude-code/src/stream/translate.ts
• packages/ai-claude-code/tests/translate.test.ts
• packages/ai/src/activities/chat/stream/processor.ts
• packages/ai/tests/stream-processor.test.ts

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📝 Walkthrough

Walkthrough

This PR fixes two issues: StreamProcessor now uses a centralized renameMessageId helper to remap placeholder-to-provider message IDs across all id-keyed structures (previously only partially updated, causing dropped tool results), and Claude Code's stream translator now emits incremental TOOL_CALL_ARGS from partial JSON deltas with deduplication against complete-message tool calls and abort flushing.

Changes

StreamProcessor Message-ID Rename Fix

Layer / File(s)	Summary
Centralized rename helper and wiring packages/ai/src/activities/chat/stream/processor.ts, packages/ai/tests/stream-processor.test.ts, .changeset/processor-message-id-rename.md	Adds renameMessageId(oldId, newId) to consistently rekey messages, messageStates, activeMessageIds, toolCallToMessage, and structured-output maps; wires it into handleTextMessageStartEvent replacing partial inline remapping; adds a regression test and changeset.

Claude Code Partial Tool-Call Argument Streaming

Layer / File(s)	Summary
SDK event type updates packages/ai-claude-code/src/stream/sdk-types.ts	Broadens content_block_start/content_block_delta payload types with optional id, name, partial_json fields.
Partial tool-use accumulation and dedup packages/ai-claude-code/src/stream/translate.ts, .changeset/stream-tool-call-args.md	Adds dedup tracking, partial tool-use state, closePartialToolUse(), and event handling for content_block_start/delta/stop and abort paths to emit incremental TOOL_CALL_ARGS/TOOL_CALL_END.
Translator tests packages/ai-claude-code/tests/translate.test.ts	Adds tests for incremental args, dedup, abort/interrupted results, message grouping, no arg bleed, and zero-argument tool calls.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant SDK as Claude Agent SDK
  participant Translator as translateSdkStream
  participant Consumer as AG-UI Event Stream
  SDK->>Translator: content_block_start (tool_use)
  Translator->>Translator: set partial tool-use state
  Translator-->>Consumer: TOOL_CALL_START (parentMessageId)
  SDK->>Translator: content_block_delta (input_json_delta)
  Translator->>Translator: accumulate partial args
  Translator-->>Consumer: TOOL_CALL_ARGS (delta)
  SDK->>Translator: content_block_stop
  Translator->>Translator: closePartialToolUse() parses JSON
  Translator-->>Consumer: TOOL_CALL_END (input)
  SDK->>Translator: complete assistant message (tool_use block)
  Translator->>Translator: skip duplicate via streamedToolCallIds

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sequenceDiagram
  participant Stream as AG-UI Stream
  participant Processor as StreamProcessor
  Stream->>Processor: TOOL_CALL_START (no parentMessageId)
  Processor->>Processor: create placeholder assistant message
  Stream->>Processor: TEXT_MESSAGE_START (real messageId)
  Processor->>Processor: renameMessageId(placeholder, real id)
  Processor->>Processor: update messages, toolCallToMessage, structured maps
  Stream->>Processor: TOOL_CALL_RESULT
  Processor-->>Stream: attach result to renamed message

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Possibly related PRs

• TanStack/ai#480: Both PRs address tool-first streaming message-id stability by routing TOOL_CALL_* events to the correct assistant message id.

Suggested reviewers: AlemTuzlak, tombeckenham

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description is informative, but it does not follow the required template and omits the checklist and release-impact sections.	Add the required Changes, checklist, and release impact sections, including the contributing/test steps and whether a changeset is needed.
Out of Scope Changes check	⚠️ Warning	The StreamProcessor message-id rename fix is a second change not requested by #901, so the PR includes extra scope beyond the linked issue.	Split the message-id rename fix into a separate PR or link an issue that explicitly requests it.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the two related changes: streaming tool-call arguments and fixing message-id renaming.
Linked Issues check	✅ Passed	The PR implements #901 by forwarding input_json_delta as incremental TOOL_CALL_ARGS and deduping partial tool calls.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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