fix(core): support ask_user reason and system message in safety checkers

[dask-58]

Summary

Adds ask_user as a valid decision type for hooks, enabling hooks to prompt users for confirmation before proceeding with an action. This aligns the hook system with the safety checker protocol which already supports ASK_USER.

Details

Problem: The hook system only documented and supported "allow" and "deny" (alias "block") for the decision field, but users needed ask_user to prompt for user confirmation.

Solution:

• Added 'ask_user' to the HookDecision type in packages/core/src/hooks/types.ts.
• Updated documentation in docs/hooks/reference.md
• Added tests for ask_user decision handling

Behavior: When a hook returns { "decision": "ask_user", "reason": "explanation" }:

• The decision is not treated as blocking (unlike deny/block)
• The CLI will prompt the user for confirmation before proceeding
• Blocking decisions (deny/block) take precedence when aggregating

Related Issues

Fixes #17872

How to Validate

1. Run unit tests for hook types:

   npm test -w @google/gemini-cli-core -- src/hooks/types.test.ts

   • Verify ask_user tests pass for isBlockingDecision() returning false

2. Run hook aggregator tests:

   npm test -w @google/gemini-cli-core -- src/hooks/hookAggregator.test.ts

   • Verify ask_user aggregation tests pass

3. Run full test suite:

   npm run typecheck && npm test

   • All 4,363+ tests should pass

4. Create a hook that returns ask_user:

   { "decision": "ask_user", "reason": "Confirm before proceeding" }

   • Verify the CLI prompts for user confirmation

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any) - None
• 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 @dask-58, 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 enhances the hook system by introducing a new decision type, ask_user, which allows hooks to prompt users for confirmation. This change aligns the hook system's capabilities with existing safety checker protocols, providing more granular control over automated processes by enabling interactive decision-making. The update ensures that user-facing prompts can be integrated seamlessly into the workflow without inherently blocking operations.

Highlights

• New Hook Decision Type: The HookDecision type now includes 'ask_user', allowing hooks to explicitly request user confirmation before proceeding with an action.
• Documentation Update: The docs/hooks/reference.md file has been updated to reflect the new 'ask_user' decision type and its behavior, clarifying that the CLI will prompt the user for confirmation.
• Test Coverage for ask_user: New unit tests have been added to verify that 'ask_user' decisions are correctly identified as non-blocking and that the HookAggregator handles them appropriately, defaulting to 'allow' when no blocking decisions are present.

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[chrstnb]

Build failed: Build process failed (no specific link errors found). Check logs for details.

[gemini-code-assist]

Code Review

This pull request adds support for the ask_user decision in hooks, aligning it with the safety checker protocol. However, a critical security vulnerability has been identified: the hook aggregation logic incorrectly treats ask_user as a standard 'allow' decision, leading to a security bypass where safety-critical user confirmations are ignored and actions are automatically permitted. The HookAggregator needs to be updated to correctly preserve and prioritize the ask_user state. Additionally, feedback includes improving documentation for the reason field's usage with ask_user and completing a new test case with a missing assertion for aggregated reasons.

[chrstnb]

Build failed: Build process failed (no specific link errors found). Check logs for details.

[chrstnb]

Build failed: Build process failed (no specific link errors found). Check logs for details.

[chrstnb]

Build failed: Build process failed (no specific link errors found). Check logs for details.

[dask-58]

@chrstnb @bdmorgan I’ve run formatting, scoped ESLint, and doc generators locally. The docs-pr-check is still failing, but I don’t have access to Cloud Build logs. Could you take a look or rerun the check?