fix(ai-gemini): dedupe functionResponse parts by id, not name

[citizen204]

Summary

When Gemini fires two or more parallel calls to the same tool in one turn, mergeConsecutiveSameRoleMessages deduped functionResponse parts by name, so the second (and any further) response to a repeated same-tool call was silently dropped. Gemini requires exactly one response part per call part in a turn, so the next request 400s:

INVALID_ARGUMENT: Please ensure that the number of function response parts is equal to the number of function call parts of the function call turn.

Every functionResponse already carries a unique id (msg.toolCallId, set at both construction sites) — keying the dedup on id instead keeps both parallel responses while still collapsing a genuine duplicate tool result (same id sent twice).

Fixes #894

Changes

• packages/ai-gemini/src/adapters/text.ts: dedupe functionResponse parts by id instead of name in mergeConsecutiveSameRoleMessages.
• packages/ai-gemini/tests/gemini-adapter.test.ts: regression test with two parallel calls to the same tool (distinct ids) — asserts both functionResponse parts survive.
• .changeset/gemini-parallel-tool-dedup.md: patch changeset.

Ran the full ai-gemini suite (vitest run in packages/ai-gemini, after building its @tanstack/ai, @tanstack/ai-event-client, @tanstack/ai-utils workspace deps) — 325 passed, 18 files.

Note: an earlier PR (#960) attempted this exact fix and was self-closed by its author for unrelated reasons ("keeping open PRs lean") after CodeRabbit review raised no substantive objections — the bug is still present on main, so re-submitting with the same diagnosis plus a parallel-call regression test.

Summary by CodeRabbit

• Bug Fixes

  • Fixed an issue where responses from parallel calls to the same tool could be dropped.
  • Prevented request errors when multiple tool calls occur in the same turn.
  • Preserved distinct responses while still removing genuine duplicates.

• Tests

  • Added coverage for parallel tool calls with separate call identifiers.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Run ID: 2be3e0a8-860b-4252-92a5-e471c430e8b0

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Reviewing files that changed from the base of the PR and between 2544a39 and d9c99cd.

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• packages/ai-gemini/tests/gemini-adapter.test.ts

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📝 Walkthrough

Walkthrough

The Gemini adapter now deduplicates functionResponse parts by tool-call ID instead of tool name. A regression test verifies that parallel calls to the same tool preserve both responses. A patch changeset records the fix.

Changes

Gemini tool response fix

Layer / File(s)	Summary
Deduplicate responses by tool-call ID .changeset/gemini-parallel-tool-dedup.md, packages/ai-gemini/src/adapters/text.ts	functionResponse deduplication now uses id, so parallel calls with the same tool name retain separate responses.
Validate parallel same-tool responses packages/ai-gemini/tests/gemini-adapter.test.ts	The regression test verifies that responses with IDs call_1 and call_2 both remain in the Gemini payload.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to d9c99

This is a localized Gemini response-deduplication fix with a regression test for parallel same-tool calls; no actionable merge-blocking risk remains beyond normal checks and review.

Possibly related PRs

• TanStack/ai#960: Implements the same Gemini response deduplication fix and regression coverage.

Suggested reviewers: alemtuzlak, tombeckenham

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main fix: deduplicating Gemini functionResponse parts by ID instead of name.
Description check	✅ Passed	The description clearly explains the bug, fix, affected files, regression test, changeset, and test results, although it omits the template checklist and release-impact sections.
Linked Issues check	✅ Passed	The changes satisfy issue #894 by deduplicating functionResponse parts by unique tool-call ID and preserving parallel same-tool responses.
Out of Scope Changes check	✅ Passed	The implementation, regression test, and patch changeset are directly related to the linked issue and PR objectives.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2 files.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[github-actions]

Thanks for the PR, @citizen204! 🙌 @AlemTuzlak will take a look.

Automated pre-review checks

• ✅ CI passing
• ✅ No merge conflicts
• ✅ Changeset present
• ⚠️ No E2E test changes detected — behavior changes need coverage under testing/e2e/ (see CONTRIBUTING)

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