feat(agy): Google Antigravity CLI hook integration

[thelok1s]

Summary

• Adds rtk hook antigravity — a PreToolUse hook for the Google Antigravity CLI (agy) that rewrites bare shell commands to their rtk-prefixed equivalents before the model executes them
• rtk init --agent agy configures ~/.gemini/antigravity-cli/settings.json with the hook and grants command(rtk) permission so retries are auto-approved
• Handles both simple (tool_name/tool_input) and rich (toolCall.name/toolCall.args) agy payload formats
• RTK_HOOK_DEBUG=1 logs full request/response pairs to ~/.local/share/rtk/agy-hook-debug.log

How it works

agy's overwrite field in PreToolHookResult is silently ignored (confirmed via debug logging — correct payload sent, original command executed). The hook therefore uses the denyReason strategy:

1. Hook intercepts run_command / Bash tool calls
2. If the command has an RTK equivalent, hook returns {"denyReason": "RTK: use 'rtk git log' instead of 'git log' (60-90% token savings)"}
3. Model reads the reason and retries with the rtk-prefixed command
4. command(rtk) in the allow list auto-approves the retry — no user prompt

Commands already prefixed with rtk or in the passthrough list pass through with {"allowTool": true}.

Test plan

• cargo test --all — 1924 tests pass, zero clippy warnings
• rtk init --agent agy writes correct ~/.gemini/antigravity-cli/settings.json
• Hook rejects bare git log with denyReason naming rtk git log
• Hook passes through rtk git log with allowTool: true
• Hook passes through non-shell tools (e.g. read_file) with allowTool: true
• RTK_HOOK_DEBUG=1 writes input/output to debug log

Known limitation

agy does not honour the overwrite field in PreToolHookResult — only allowTool and denyReason are implemented. The deny-and-retry pattern produces a ⚠ Tool call denied notice in the agy UI before the model retries with the RTK command. Transparent rewriting will be possible once agy implements overwrite support.

This issue reported in this topic on discuss.ai.google.dev. More visibility on this bug report required.

Tested in Antigravity CLI v1.0.2

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds first-class support for Google Antigravity CLI (agy) by introducing a dedicated hook command and installer, while also hardening UTF-8 boundary handling in a couple of string-slicing utilities.

Changes:

• Add a new Agy agent target and rtk hook antigravity hook command path.
• Implement agy CLI install/uninstall logic that patches ~/.gemini/config/hooks.json and updates agy permissions in settings.json.
• Replace floor_char_boundary usages with manual UTF-8 boundary adjustment loops to avoid panics.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/main.rs	Adds Agy agent + hook subcommand wiring and uninstall dispatch updates.
src/hooks/init.rs	Implements agy CLI init/uninstall, hooks.json patching, and permission allow-list updates.
src/hooks/hook_cmd.rs	Adds run_antigravity hook handler and extends Gemini hook to detect a “rich” payload shape.
src/hooks/constants.rs	Introduces new constants for agy CLI subdir/layout.
src/cmds/system/pipe_cmd.rs	Avoids UTF-8 slicing panic by adjusting to char boundaries manually.
src/cmds/system/json_cmd.rs	Avoids UTF-8 slicing panic when truncating long strings.
hooks/antigravity/README.md	Updates documentation to describe Antigravity IDE vs agy CLI integration.

[thelok1s]

Resolves #1975

[webermaster]

This would be very useful. any idea on when it might be resolved?

[KuSh]

Closing in favour of #3711, which adds the same native Antigravity PreToolUse hook on the canonical antigravity target. Both of the current Antigravity pull requests rewrite the command through the overwrite field, with a live capture from a recent agy build showing it is honoured, so the deny-with-reason strategy here is no longer needed. If you have newer evidence that overwrite is still ignored, or you meant the separate agy target to stay its own integration, please say so on #3711 or reply here.