feat(cli): defer devtools startup and integrate with F12

[SandyTao520]

TLDR

Refactor DevTools and Activity Logger to start intercepting events immediately but defer server startup until needed. If an existing DevTools server is already running, connect to it eagerly at startup. F12 opens the browser (starting a server first only if none exists).

Dive Deeper

• Immediate Interception, Deferred Start: If devtools: true is set, the CLI starts intercepting network and console logs immediately in a memory buffer. The DevTools server only starts when F12 is pressed — unless one is already running.
• Eager Probe at Startup: On launch, the CLI probes the default DevTools port. If a server is already running (e.g. from another CLI instance), it connects immediately and begins streaming logs — no F12 required.
• F12 Short-Circuit: If already connected to an existing server, F12 simply opens the browser. Otherwise it starts a new server, connects, then opens the browser.
• "Last 10" Buffering: A rolling buffer in ActivityLogger keeps only the last 10 network requests and last 10 console logs, preventing memory leaks while ensuring recent context is available when the UI opens.
• Race Handling & Promotion: If the CLI loses the default port race, it stops its own server and connects to the winner. If the winner dies, the CLI promotes itself to server via handlePromotion (capped at 3 attempts).
• Deduplication: Concurrent startDevToolsServer calls return the same promise.
• Strong Typing & Linting: Cleaned up many any usages and removed eslint-disable directives in activityLogger.ts.

Reviewer Test Plan

1. Set "devtools": true in your .gemini/settings.json.
2. Start the CLI and perform some actions (e.g., run a prompt).
3. Press F12.
4. Verify the browser opens to the DevTools UI (http://127.0.0.1:25417).
5. Verify the last 10 requests/logs are visible in the UI.
6. Verify the internal debug drawer did NOT open in the terminal.
7. Start a second CLI instance — it should connect to the existing server automatically (no F12 needed) and logs should appear in the same DevTools UI.
8. (Optional) Simulate a browser failure (e.g., set BROWSER=false) and verify the internal drawer opens with the URL message.

Testing Matrix

	🍏	🪟	🐧
npm run	✅	❓	❓
npx	✅	❓	❓
Docker	❓	❓	❓
Podman	❓	-	-
Seatbelt	❓	-	-

Linked issues / bugs

Progress on internal requests for better DevTools UX.

[gemini-cli]

Hi @SandyTao520, 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!

[gemini-cli]

Hi there! Thank you for your contribution to Gemini CLI.

To improve our contribution process and better track changes, we now require all pull requests to be associated with an existing issue, as announced in our recent discussion and as detailed in our CONTRIBUTING.md.

This pull request is being closed because it is not currently linked to an issue. Once you have updated the description of this PR to link an issue (e.g., by adding Fixes #123 or Related to #123), it will be automatically reopened.

How to link an issue:
Add a keyword followed by the issue number (e.g., Fixes #123) in the description of your pull request. For more details on supported keywords and how linking works, please refer to the GitHub Documentation on linking pull requests to issues.

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

[gemini-code-assist]

Summary of Changes

Hello @SandyTao520, 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 significantly refactors the DevTools and Activity Logger integration within the CLI to enhance user experience and performance. By deferring the DevTools server startup and UI opening until explicitly triggered, the CLI can initialize faster. Concurrently, an intelligent buffering mechanism ensures that critical recent activity is captured and available for inspection once DevTools are launched, providing a seamless debugging experience without unnecessary resource consumption.

Highlights

• Deferred DevTools Startup: The DevTools server and UI now only start when explicitly requested by the user (e.g., via F12), rather than immediately on CLI startup, improving initial performance.
• Activity Buffering: The ActivityLogger now buffers the last 10 network requests and console logs in memory, ensuring recent context is available when DevTools are opened without causing memory leaks.
• F12 Integration: Pressing F12 in the CLI will now attempt to open the DevTools UI in the default browser. If the browser fails to open, a fallback message with the DevTools URL is displayed in the terminal.
• Improved Type Safety: Numerous any type usages and eslint-disable comments were removed from activityLogger.ts, enhancing code quality and maintainability.
• Test Stability: Increased timeouts for several flaky tests in the core package to prevent preflight failures.

Changelog

• packages/cli/src/gemini.tsx
  • Updated the import and usage of registerActivityLogger to setupInitialActivityLogger to reflect the new deferred DevTools initialization.
• packages/cli/src/ui/AppContainer.tsx
  • Modified the F12 key handler to conditionally start the DevTools server and attempt to open the UI in the default browser if DevTools are enabled.
  • Implemented a fallback mechanism to display the DevTools URL in the terminal if browser opening fails.
  • Added historyManager and settings.merged.general.devtools to the useEffect dependency array for proper reactivity.
• packages/cli/src/ui/hooks/slashCommandProcessor.ts
  • Added setPendingItem to the useCallback dependency array.
• packages/cli/src/utils/activityLogger.test.ts
  • Added a new test file to verify the buffering behavior of ActivityLogger for network requests and console logs, ensuring only the last 10 items are retained and buffers are cleared after retrieval.
• packages/cli/src/utils/activityLogger.ts
  • Removed several eslint-disable comments and improved type annotations, including importing ConsoleLogPayload and introducing PartialNetworkLog.
  • Implemented networkBuffer, consoleBuffer, and bufferLimit properties to manage activity buffering.
  • Added getBufferedLogs() method to retrieve and clear the buffered network and console logs.
  • Updated sanitizeNetworkLog to correctly handle PartialNetworkLog and improved type checking for headers.
  • Modified safeEmitNetwork and logConsole methods to push events into their respective buffers.
  • Refactored patchNodeHttp to use ActivityLogger.getInstance() for consistent singleton access and improved type safety for request handling.
  • Renamed the internal buffer to transportBuffer within setupNetworkLogging to distinguish it from the new activity buffers.
  • Enhanced handleServerMessage and sendMessage with more specific type definitions.
  • Updated flushBuffer to first flush the newly introduced activity buffers (network and console) and then the transportBuffer when network logging is enabled.
• packages/cli/src/utils/devtoolsService.test.ts
  • Added a mock for ActivityLogger.getInstance to control its behavior in tests.
  • Updated imports to reflect the new setupInitialActivityLogger and startDevToolsServer functions.
  • Rewrote tests to validate the new DevTools initialization flow, including initial buffering and deferred server startup/connection logic.
  • Adjusted the extraction of the onReconnectFailed callback in promotion tests to match the updated addNetworkTransport signature.
• packages/cli/src/utils/devtoolsService.ts
  • Imported ActivityLogger for direct instance access.
  • Refactored the registerActivityLogger function into two distinct functions: setupInitialActivityLogger and startDevToolsServer.
  • setupInitialActivityLogger now initializes the ActivityLogger in a buffering-only mode and disables network logging, allowing immediate event interception without starting the server.
  • startDevToolsServer is responsible for probing for an existing DevTools server, starting a new one if none is found, adding the network transport, and enabling network logging.
  • The original registerActivityLogger now acts as a legacy wrapper, calling the new functions sequentially.
• packages/core/src/services/fileDiscoveryService.test.ts
  • Increased the timeout for several tests to 10000ms to prevent flakiness.
• packages/core/src/tools/read-file.test.ts
  • Increased the timeout for the 'should handle image file and return appropriate content' test to 10000ms.

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[gemini-code-assist]

Code Review

This pull request refactors the DevTools activity logger to defer server startup until explicitly requested, improving user experience, and introduces a rolling buffer for recent logs to manage memory. A security audit, however, identified two high-severity vulnerabilities: the CLI insecurely trusts any process listening on a specific local port as a legitimate DevTools server, which could lead to sensitive session data disclosure on multi-user systems. Furthermore, the activity logger fails to redact sensitive API keys when they are passed as query parameters in URLs, potentially leading to credential leakage in logs. Additionally, some network log events are missing timestamps, which will cause them to be displayed out of order. Please ensure this timestamp fix is applied to the modified code and similar calls in patchGlobalFetch.

[github-actions]

Size Change: +6.39 kB (+0.03%)

Total Size: 23.9 MB

Filename	Size	Change
./bundle/gemini.js	23.9 MB	+6.39 kB (+0.03%)

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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[gemini-cli]

Hi there! Thank you for your contribution to Gemini CLI.

To improve our contribution process and better track changes, we now require all pull requests to be associated with an existing issue, as announced in our recent discussion and as detailed in our CONTRIBUTING.md.

This pull request is being closed because it is not currently linked to an issue. Once you have updated the description of this PR to link an issue (e.g., by adding Fixes #123 or Related to #123), it will be automatically reopened.

How to link an issue:
Add a keyword followed by the issue number (e.g., Fixes #123) in the description of your pull request. For more details on supported keywords and how linking works, please refer to the GitHub Documentation on linking pull requests to issues.

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