feat: add compactToolOutputAllowlist setting

[dolphprefect]

feat: add compactToolOutputAllowlist setting

Introduces a new UI setting compactToolOutputAllowlist (string[]) that extends the built-in compact tool output list. When compactToolOutput is enabled, any tool whose name appears in this list is rendered using the compact DenseToolMessage instead of the full ToolResultDisplay.

This allows external tools (e.g. MCP servers) to opt in to compact rendering by adding their tool names during setup, without requiring changes to the built-in allowlist.

Summary

The existing compactToolOutput setting collapses verbose tool output into a single summary line, but only for a hardcoded set of built-in Gemini tools. MCP server tools — which can have any name and are user-defined — were always rendered verbosely regardless of this setting.

This PR adds a compactToolOutputAllowlist UI setting (string array, default empty) that extends the built-in list at runtime. Any tool name in the allowlist is treated as compact-eligible when compactToolOutput is enabled. MCP server setup scripts can populate this list in settings.json so their tools benefit from compact rendering without requiring upstream code changes.

Details

• compactToolOutputAllowlist is defined in settingsSchema.ts as an array of strings, not shown in the settings dialog (it's intended for programmatic population by tool setup scripts).
• isCompactTool() in ToolGroupMessage.tsx gains an optional extraAllowlist parameter (defaults to []) checked alongside the built-in COMPACT_OUTPUT_ALLOWLIST.
• All call sites in ToolGroupMessage.tsx and useGeminiStream.ts pass the allowlist read from settings. Hook dependency arrays updated accordingly.
• No behaviour change for existing users — the allowlist defaults to empty.

Related Issues

How to Validate

1. Add tool names to ~/.gemini/settings.json:

   {
     "ui": {
       "compactToolOutput": true,
       "compactToolOutputAllowlist": ["my_mcp_tool"]
     }
   }

2. Configure an MCP server that exposes a tool named my_mcp_tool.
3. Start Gemini CLI and trigger a call to my_mcp_tool.
4. Confirm the result renders as a single compact line (tool name + summary) rather than the full output block.
5. Set compactToolOutput: false and confirm the tool reverts to full output (allowlist has no effect when compact mode is off).
6. Remove the tool name from the allowlist and confirm it reverts to full output.

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, 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 flexible mechanism for users to control which tools are rendered in a compact format. By adding a configurable allowlist, users can now enable compact output for custom or external tools, such as those provided by MCP servers, without requiring changes to the core codebase. This improves the UI experience for users with custom tool integrations.

Highlights

• New Configuration Setting: Introduced compactToolOutputAllowlist in settingsSchema.ts to allow users to specify additional tools for compact rendering.
• Logic Update: Updated isCompactTool in ToolGroupMessage.tsx to accept an optional allowlist, enabling custom tools (like MCP servers) to be rendered compactly.
• Integration: Updated all call sites in ToolGroupMessage.tsx and useGeminiStream.ts to pass the new allowlist from settings, ensuring consistent behavior across the UI.

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[gemini-code-assist]

Code Review

This pull request introduces a compactToolOutputAllowlist setting to the CLI configuration, allowing users to specify additional tools for compact display. The changes update the settings schema and integrate the allowlist into the ToolGroupMessage component and useGeminiStream hook. Feedback suggests memoizing the allowlist as a Set to optimize lookup performance from O(N) to O(1) within frequently called rendering functions.

[dolphprefect]

Closed in favor of the much simpler proposal #25912