fix(core): avoid duplicate tool response turns when resuming sessions by diegogodinezr · Pull Request #29618 · google-gemini/gemini-cli

diegogodinezr · 2026-10-02T21:33:10Z

Summary

Prevent duplicate tool response turn deserialization in convertSessionToClientHistory when resuming recorded sessions.

Details

When reconstructing client history during session resume, convertSessionToClientHistory previously replayed recorded user functionResponse turns while also synthesizing ${msg.id}_response turns from toolCalls[].result on the preceding model message. This resulted in redundant history synthesis and mismatched pairing alignment between functionCall and functionResponse entries.

This change:

Checks whether subsequent user messages before the next model turn already supply functionResponse entries for the model turn's toolCalls, skipping redundant synthesis while retaining fallback synthesis from toolCalls[].result for legacy session recordings.
Filters out duplicate functionResponse entries with the same id within a single tool exchange round so existing recordings with duplicated entries deserialize cleanly.
Adds unit test coverage in packages/core/src/utils/sessionUtils.test.ts for modern session recordings, legacy session recordings, parallel tool calls, and duplicate entry filtering.

Related Issues

Fixes #29365

How to Validate

Run the unit test suite for sessionUtils:

npm test -w @google/gemini-cli-core -- src/utils/sessionUtils.test.ts

Pre-Merge Checklist

When reconstructing client history during session resume, convertSessionToClientHistory replays recorded user response turns while also re-synthesizing response turns from toolCalls[].result on preceding model turns. This change: - Checks whether recorded user response turns are already present before synthesizing from toolCalls[].result, retaining fallback synthesis for legacy recordings. - Filters out duplicate functionResponse entries matching the same callId within a single turn. - Adds test coverage for single tool calls, parallel tool calls, legacy formats, and deduplication.

gemini-code-assist · 2026-10-02T21:33:21Z

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue where resuming recorded sessions caused duplicate tool response turns. By intelligently checking for existing user-provided responses before synthesizing them from model tool calls and implementing deduplication logic, the history reconstruction process is now more robust and prevents redundant entries.

Highlights

Duplicate Tool Response Prevention: Updated convertSessionToClientHistory to detect and skip redundant synthesis of tool responses when a recorded user message already contains the corresponding functionResponse.
Response Deduplication: Implemented a seenFunctionResponseIds tracker to filter out duplicate functionResponse entries within a single tool exchange round, ensuring cleaner deserialization.
Enhanced Test Coverage: Added comprehensive unit tests in packages/core/src/utils/sessionUtils.test.ts covering modern and legacy session recordings, parallel tool calls, and corrupted history scenarios.

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github-actions · 2026-10-02T21:33:28Z

📊 PR Size: size/L

Lines changed: 547
Additions: +527
Deletions: -20
Files changed: 2

gemini-code-assist

Code Review

This pull request updates the convertSessionToClientHistory function in sessionUtils.ts to prevent duplicate tool response turns and deduplicate functionResponse parts in the conversation history. It tracks processed function response IDs using a set and looks ahead at subsequent user messages to avoid synthesizing duplicate tool responses. Unit tests have been updated and added to verify these deduplication behaviors. I have no feedback to provide.

diegogodinezr · 2026-10-02T21:36:16Z

/gemini review

gemini-code-assist

Code Review

This pull request enhances convertSessionToClientHistory in packages/core/src/utils/sessionUtils.ts to deduplicate function response IDs and avoid synthesizing duplicate tool response turns when they are already recorded in subsequent user messages. It also adds unit tests to verify these deduplication scenarios. The review feedback suggests utilizing a pendingPartsToAppend map to merge synthesized tool responses into the correct subsequent user turns, preventing consecutive user turns and keeping parallel tool responses grouped together.

…ser turn

diegogodinezr · 2026-10-02T21:46:52Z

/gemini review

gemini-code-assist

Code Review

This pull request refactors convertSessionToClientHistory in sessionUtils.ts to deduplicate tool response turns and prevent duplicate tool responses when a recorded user functionResponse turn follows. It also adds comprehensive test cases to verify these behaviors. However, a potential runtime error was identified where msg.content can be undefined or null, which would cause a crash when processing user messages. A fix is recommended to safely handle optional properties.

…sionToClientHistory

diegogodinezr · 2026-10-02T21:54:11Z

/gemini review

gemini-code-assist

Code Review

This pull request updates the convertSessionToClientHistory function in packages/core/src/utils/sessionUtils.ts to improve the handling of tool responses and prevent duplication. The changes introduce logic to track and deduplicate function responses, ensuring that tool calls are correctly merged into subsequent user turns instead of creating redundant response turns. Additionally, the test suite in packages/core/src/utils/sessionUtils.test.ts has been expanded with several new test cases to verify these deduplication and merging behaviors, as well as to ensure robust handling of user messages with undefined content. I have no feedback to provide as there were no review comments.

DavidAPierce · 2026-10-06T19:27:11Z

Findings

🔴 Critical / High Priority

None identified. The fix directly solves the duplicate response problem, gracefully repairs already-corrupted historical session files, and preserves full backwards compatibility for legacy recordings.

🟡 Improvements

JSDoc Documentation for convertSessionToClientHistory Behavior
- File: packages/core/src/utils/sessionUtils.ts (lines 107–112)
- Observation: The behavior of convertSessionToClientHistory now incorporates sophisticated lookahead and merge logic to reconcile modern vs. legacy tool response recordings. Adding a brief JSDoc note explaining the forward-scan and merge strategy will help future contributors understand how tool call results are reconciled with recorded user turns.

🟢 Nitpicks

Map Cleanup Lifecycle
- File: packages/core/src/utils/sessionUtils.ts (lines 115, 122)
- Observation: Once extraParts are retrieved from pendingPartsToAppend.get(msg.id), calling pendingPartsToAppend.delete(msg.id) allows the buffered parts to be garbage collected immediately during large session reconstruction.

… clean up pending map

diegogodinezr requested a review from a team as a code owner October 2, 2026 21:33

github-actions Bot added the size/l A large sized PR label Oct 2, 2026

gemini-code-assist Bot reviewed Oct 2, 2026

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Comment thread packages/core/src/utils/sessionUtils.ts

Comment thread packages/core/src/utils/sessionUtils.ts

gemini-cli Bot added priority/p1 Important and should be addressed in the near term. area/core Issues related to User Interface, OS Support, Core Functionality labels Oct 2, 2026

fix(core): merge pending synthesized tool responses into subsequent u…

64bd7fc

…ser turn

gemini-code-assist Bot reviewed Oct 2, 2026

View reviewed changes

Comment thread packages/core/src/utils/sessionUtils.ts Outdated

fix(core): safely handle undefined user message content in convertSes…

6c79f20

…sionToClientHistory

gemini-code-assist Bot reviewed Oct 2, 2026

View reviewed changes

This was referenced Oct 2, 2026

📊 AI CLI 工具社区动态日报 2026-10-03 litang9/big_model_radar#488

Open

📊 AI CLI 工具社区动态日报 2026-10-03 96loveslife/big_model_radar#580

Open

docs(core): document convertSessionToClientHistory merge strategy and…

b08d8a9

… clean up pending map

DavidAPierce approved these changes Oct 6, 2026

View reviewed changes

DavidAPierce enabled auto-merge October 6, 2026 20:19

DavidAPierce added this pull request to the merge queue Oct 6, 2026

Merged via the queue into google-gemini:main with commit 486ae2c Oct 6, 2026
33 checks passed

github-actions Bot mentioned this pull request Oct 6, 2026

📊 AI CLI 工具社区动态日报 2026-10-07 litang9/big_model_radar#508

Open

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fix(core): avoid duplicate tool response turns when resuming sessions - #29618

fix(core): avoid duplicate tool response turns when resuming sessions#29618
DavidAPierce merged 4 commits into
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diegogodinezr:GH-29365

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