fix(voice-agent): prevent conversation history race and dangling pointers during LLM generation

[Adityakk9031]

Description

In core/src/features/voice_agent/voice_agent_d7_abi.cpp, d7_process_utterance creates raw string pointers (const char*) from handle->conversation_history into llm_opts.history.

To ensure safe string lifetimes during LLM generation and prevent data races with concurrent turn completion or session cleanup/destruction:

1. history_snapshot copies handle->conversation_history into local stack storage under the outer handle->mutex, guaranteeing valid string pointers for llm_opts.history throughout the full duration of rac_llm_generate.
2. Redundant nested locks on non-recursive handle->mutex were eliminated to prevent potential deadlocks.
3. Added full Doxygen docstring documentation to d7_process_utterance.

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactoring

Testing

• Lint passes locally
• Added/updated tests for changes

Platform-Specific Testing (check all that apply)

Swift SDK / iOS Sample:

• Tested on Mac (macOS target)

Kotlin SDK / Android Sample:

• Tested on Android Phone (Emulator or Device)

Flutter SDK / Flutter Sample:

• Tested on Android

React Native SDK / React Native Sample:

• Tested on Android

Web SDK / Web Sample:

• Tested in Chrome (Desktop)

Labels

Please add the appropriate label(s):

SDKs:

• Swift SDK - Changes to Swift SDK (bindings/swift)
• Kotlin SDK - Changes to Kotlin SDK (bindings/kotlin)
• Flutter SDK - Changes to Flutter SDK (bindings/flutter)
• React Native SDK - Changes to React Native SDK (bindings/react-native)
• Web SDK - Changes to Web SDK (bindings/web)
• Commons - Changes to shared native code (core)

Sample Apps:

• Flutter Sample - Changes to Flutter example app (bindings/flutter/example)
• React Native Sample - Changes to React Native example app (bindings/react-native/example)
• Minimal Examples - Changes to an in-repo SDK harness (bindings/{swift,kotlin,web}/example)

Checklist

• Code follows project style guidelines
• Self-review completed
• Documentation updated (if needed)

Screenshots

N/A - C++ Core Engine & Audio Pipeline synchronization fix.

Summary by CodeRabbit

• Bug Fixes
  • Improved voice agent reliability during concurrent conversation processing.
  • Improved consistency when updating conversation history while responses are being generated.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Team

Run ID: d539cfcf-cd4f-4ab9-96ff-8676df1f6cd9

📥 Commits

Reviewing files that changed from the base of the PR and between a1a0212 and 403341c.

📒 Files selected for processing (1)

• core/src/features/voice_agent/voice_agent_d7_abi.cpp

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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📝 Walkthrough

Walkthrough

d7_process_utterance now documents its processing pipeline and uses the existing handle->mutex lock when it snapshots conversation history for LLM generation.

Changes

Voice history synchronization

Layer / File(s)	Summary
Document and synchronize utterance processing core/src/features/voice_agent/voice_agent_d7_abi.cpp	Documentation describes d7_process_utterance, including synchronization and return values. History snapshot construction uses the existing function-level mutex without nested locking.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to 40334

This change synchronizes conversation-history snapshots and updates during voice generation, preventing concurrent history access races. No current merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The description is complete and follows the repository template. It explains the race and dangling-pointer fix, identifies the change as a bug fix, records testing, selects the Commons label, and comp…
Title check	✅ Passed	The title clearly summarizes the primary change: preventing conversation-history races and dangling pointers during LLM generation in the voice agent.

Full details: Description check

Explanation

The description is complete and follows the repository template. It explains the race and dangling-pointer fix, identifies the change as a bug fix, records testing, selects the Commons label, and completes the checklist and screenshots section.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Actionable comments posted: 1

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Inline comments:
In `@core/src/features/voice_agent/voice_agent_d7_abi.cpp`:
- Line 770: Remove the nested handle->mutex lock guards in d7_process_utterance
at both the pre-generation block and the post-response block, relying on the
function’s existing outer lock; alternatively, narrow the outer lock scope so
neither acquisition overlaps it while preserving synchronization.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Team

Run ID: 00bc58df-eae2-4c17-ad7a-d82944580227

📥 Commits

Reviewing files that changed from the base of the PR and between 45e9127 and a1a0212.

📒 Files selected for processing (1)

• core/src/features/voice_agent/voice_agent_d7_abi.cpp

Included review availability: Your plan provides up to 10 included reviews per hour; 8 remain after this review.

[Adityakk9031]

@sanchitmonga22 have a look

[sanchitmonga22]

Replying to this comment

Thanks for the ping, @Adityakk9031! Took a full look -- approving and merging now. Appreciate you tightening up the mutex handling here.

Reviewed with help from Claude Code and Codex.

[sanchitmonga22]

Thanks a lot for this, @Adityakk9031! This snapshots handle->conversation_history into a local vector before building the LLM's history options for a turn, so the string pointers handed into LLM generation are guaranteed to stay valid for the call, and it removes a mutex double-lock that an earlier commit on this branch had introduced along the way.

Checked: CodeRabbit reviewed the latest commit · CI green · built and linted locally merged into main (C++ commons and engines) · two independent code reviews.

One optional note for later, not blocking: handle->mutex already covers the whole VAD→STT→LLM→TTS turn today, so there wasn't an active race on main -- this lands as forward-looking hardening rather than a fix for a live bug. Worth keeping in mind if that locking is ever narrowed.

Merging now -- really appreciate the contribution!

Reviewed with help from Claude Code and Codex.