feat(core): add LocalSubagentProtocol behind AgentProtocol

[adamfweidman]

Summary

• Introduces LocalSubagentProtocol which wraps LocalAgentExecutor behind the AgentProtocol interface, translating SubagentActivityEvent callbacks into AgentEvents
• Exposes LocalSubagentSession (extends AgentSession) as the public API with getResult() for obtaining the executor's OutputObject
• Supports multi-send: after agent_end, a new send({message}) starts a fresh stream with a new result promise
• Adds export from packages/core/src/index.ts

Design notes

• _resultPromise is created per-stream in _beginNewStream(), not in the constructor — enables multi-send semantics
• Buffered config (send({update})) is consumed and cleared on each message send to prevent config bleed across sends
• Activity translation maps THOUGHT_CHUNK, TOOL_CALL_START, TOOL_CALL_END, and ERROR to the corresponding AgentEvent types

Test plan

• 37 unit tests covering:
  • Stream lifecycle (agent_start → message → agent_end)
  • Activity event translation (thoughts, tool calls, errors)
  • Abort/cancellation propagation
  • Concurrent send guard
  • Buffered config via send({update})
  • Multi-send sequential sends, latest result tracking, config isolation, pre-send getResult guard, fresh events per stream
• npm run build --workspace=packages/core passes

[gemini-cli]

Hi @adamfweidman, thank you so much for your contribution to Gemini CLI! We really appreciate the time and effort you've put into this.

We're making some updates to our contribution process to improve how we track and review changes. Please take a moment to review our recent discussion post: Improving Our Contribution Process & Introducing New Guidelines.

Key Update: Starting January 26, 2026, the Gemini CLI project will require all pull requests to be associated with an existing issue. Any pull requests not linked to an issue by that date will be automatically closed.

Thank you for your understanding and for being a part of our community!

[github-actions]

🛑 Action Required: Evaluation Approval

Steering changes have been detected in this PR. To prevent regressions, a maintainer must approve the evaluation run before this PR can be merged.

Maintainers:

1. Go to the Workflow Run Summary.
2. Click the yellow 'Review deployments' button.
3. Select the 'eval-gate' environment and click 'Approve'.

Once approved, the evaluation results will be posted here automatically.

[gemini-code-assist]

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 introduces a new LocalSubagentProtocol that bridges the LocalAgentExecutor with the standard AgentProtocol interface. This enhancement allows local agents to seamlessly emit AgentEvents, providing a consistent event stream for their activities. It also enables robust multi-send functionality, where agents can handle sequential interactions, and includes mechanisms for buffering configuration updates and managing stream lifecycles, ultimately improving the flexibility and integration of local subagents within the system.

Highlights

• New Protocol Implementation: Introduced LocalSubagentProtocol to integrate LocalAgentExecutor with the AgentProtocol interface, translating SubagentActivityEvent callbacks into standard AgentEvents.
• Public API for Sessions: Exposed LocalSubagentSession (extending AgentSession) as the public API, providing a getResult() method to retrieve the executor's OutputObject.
• Multi-Send Capability: Implemented support for multi-send, allowing new streams to start with fresh result promises after an agent_end event.
• Configuration Buffering: Added logic to buffer configuration updates via send({update}) and apply them to subsequent send({message}) calls, ensuring config isolation across sends.
• Module Export: Exported LocalSubagentSession from the packages/core/src/index.ts file.

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[github-actions]

Size Change: -4 B (0%)

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[gemini-code-assist]

Code Review

This pull request introduces the LocalSubagentProtocol and LocalSubagentSession classes to wrap LocalAgentExecutor within the standard AgentProtocol interface. This implementation handles the translation of internal subagent activity events into standard agent events, manages session lifecycle (start, end, abort), and provides a mechanism to retrieve the final execution result. Additionally, a comprehensive test suite has been added to verify event sequencing, configuration buffering, and error handling. I have no feedback to provide as the implementation is robust and follows the project's architectural patterns.

[adamfweidman]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces the LocalSubagentProtocol and LocalSubagentSession classes to wrap the LocalAgentExecutor within the standard AgentProtocol interface. This allows local subagents to be used consistently with other protocol implementations by translating internal activity events into standard agent events. The accompanying test suite provides comprehensive coverage for lifecycle events, configuration buffering, activity translation, and concurrent execution guards. Feedback is provided regarding input sanitization to prevent prompt injection and ensuring string parameters from tools are properly trimmed and validated.

[gemini-cli]

Hi there! Thank you for your interest in contributing to Gemini CLI.

To ensure we maintain high code quality and focus on our prioritized roadmap, we have updated our contribution policy (see Discussion #17383).

We only guarantee review and consideration of pull requests for issues that are explicitly labeled as 'help wanted'. All other community pull requests are subject to closure after 14 days if they do not align with our current focus areas. For this reason, we strongly recommend that contributors only submit pull requests against issues explicitly labeled as 'help-wanted'.

This pull request is being closed as it has been open for 14 days without a 'help wanted' designation. We encourage you to find and contribute to existing 'help wanted' issues in our backlog! Thank you for your understanding and for being part of our community!

[gemini-cli]

This pull request is being closed as it has been open for 14 days without a 'help wanted' designation. We encourage you to find and contribute to existing 'help wanted' issues in our backlog! Thank you for your understanding.

[gemini-cli]

This pull request is being closed as it has been open for 14 days without a 'help wanted' designation. We encourage you to find and contribute to existing 'help wanted' issues in our backlog! Thank you for your understanding.

[jacob314]

[adamfweidman]

Part of #22700 work