feat(cli): implement event-driven tool execution scheduler

[abhipatel12]

Summary

Implement the event-driven tool execution scheduler and integrate it into the
CLI UI via a facade hook. This completes the "Bridge" phase of the ReAct loop
migration, allowing for seamless toggling between legacy and modern execution
engines.

Details

• Event-Driven Hook: Introduced useToolExecutionScheduler.ts, which
  utilizes the new Core Scheduler and MessageBus.
• Adapter Pattern: Implemented a robust adapter within the hook to inject
  MessageBus-proxying onConfirm callbacks into Core objects, maintaining
  compatibility with legacy UI components.
• Facade Hook: Created useToolScheduler.ts to act as a single entry point
  for useGeminiStream, switching implementations based on the experimental
  flag.
• Type Safety: Unified tool tracking types to ensure a stable data contract
  across both implementations.
• Verification:
  • Added useToolExecutionScheduler.test.ts (400+ lines of coverage).
  • Added useToolSchedulerFacade.test.ts to verify conditional delegation.
  • Updated useGeminiStream.test.tsx to reflect the new facade integration.

Related Issues

Related to #14306

How to Validate

1. Unit Tests:
   • npm test -w @google/gemini-cli -- src/ui/hooks/useToolExecutionScheduler.test.ts
   • npm test -w @google/gemini-cli -- src/ui/hooks/useToolSchedulerFacade.test.ts
   • npm test -w @google/gemini-cli -- src/ui/hooks/useGeminiStream.test.tsx
2. Manual Verification:
   • Enable the scheduler: "enableEventDrivenScheduler": true in settings.json
   • Execute tool-heavy prompts (e.g., replace or write_file) and verify:
     • Real-time execution status updates.
     • Confirmation dialogs correctly trigger execution upon approval.
     • Auto-approval (Shift+Tab) works as expected.

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any)
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker

[gemini-code-assist]

Summary of Changes

Hello @abhipatel12, 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 event-driven tool execution scheduler, marking a significant step in migrating the CLI's execution engine. By implementing a facade hook, the system can seamlessly toggle between the existing legacy scheduler and the new, more modern event-driven approach. This change enhances the underlying architecture by utilizing a MessageBus for communication and a dedicated Scheduler from the core, while an adapter layer ensures that the UI remains compatible with the new system without requiring extensive refactoring.

Highlights

• Event-Driven Scheduler Implementation: Introduced useToolExecutionScheduler.ts which leverages the new Core Scheduler and MessageBus for managing tool execution.
• Facade Integration: A new useToolScheduler.ts hook acts as a facade, dynamically switching between the legacy useReactToolScheduler and the new event-driven scheduler based on a configuration flag.
• Adapter Pattern for UI Compatibility: An adapter within useToolExecutionScheduler injects MessageBus-proxying onConfirm callbacks into Core objects, ensuring backward compatibility with existing UI components.
• Unified Type Safety: Tool tracking types have been unified to provide a consistent data contract across both legacy and modern implementations.
• Extensive Test Coverage: New unit tests (useToolExecutionScheduler.test.ts, useToolSchedulerFacade.test.ts) and updates to existing tests (useGeminiStream.test.tsx) ensure robust verification of the new scheduler and its integration.

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[gemini-code-assist]

Code Review

This pull request introduces a well-architected, event-driven tool execution scheduler. The use of a facade hook (useToolScheduler) to toggle between the legacy and new schedulers is an excellent approach for this migration. The adapter pattern in useToolExecutionScheduler is cleanly implemented to maintain compatibility with existing UI components by injecting onConfirm callbacks. The new code is accompanied by comprehensive tests, ensuring the new scheduler and the facade logic are robust. Overall, this is a high-quality contribution that modernizes the tool execution flow while ensuring a seamless transition.

[github-actions]

Size Change: +35.4 kB (+0.15%)

Total Size: 23.2 MB

Filename	Size	Change
./bundle/gemini.js	23.2 MB	+35.4 kB (+0.15%)

ℹ️ View Unchanged

Filename	Size
./bundle/sandbox-macos-permissive-closed.sb	1.03 kB
./bundle/sandbox-macos-permissive-open.sb	890 B
./bundle/sandbox-macos-permissive-proxied.sb	1.31 kB
./bundle/sandbox-macos-restrictive-closed.sb	3.29 kB
./bundle/sandbox-macos-restrictive-open.sb	3.36 kB
./bundle/sandbox-macos-restrictive-proxied.sb	3.56 kB

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