feat(agy): Google Antigravity CLI hook integration

README.md

@@ -106,10 +106,11 @@ rtk init -g                     # Claude Code / Copilot (default)
 rtk init -g --gemini            # Gemini CLI
 rtk init -g --codex             # Codex (OpenAI)
 rtk init -g --agent cursor      # Cursor
+rtk init -g --agent agy         # Google Antigravity CLI (agy)
 rtk init --agent windsurf       # Windsurf
 rtk init --agent cline          # Cline / Roo Code
 rtk init --agent kilocode       # Kilo Code
-rtk init --agent antigravity    # Google Antigravity
+rtk init --agent antigravity    # Google Antigravity IDE (rules-based)
 rtk init --agent hermes         # Hermes
 
 # 2. Restart your AI tool, then test
@@ -351,7 +352,7 @@ rtk git status
 
 ## Supported AI Tools
 
-RTK supports 13 AI coding tools. Each integration rewrites shell commands to `rtk` equivalents for 60-90% token savings where the agent supports command interception.
+RTK supports 14 AI coding tools. Each integration rewrites shell commands to `rtk` equivalents for 60-90% token savings where the agent supports command interception.
 
 | Tool | Install | Method |
 |------|---------|--------|
@@ -360,6 +361,7 @@ RTK supports 13 AI coding tools. Each integration rewrites shell commands to `rt
 | **GitHub Copilot CLI** | `rtk init -g --copilot` | PreToolUse deny-with-suggestion (CLI limitation) |
 | **Cursor** | `rtk init -g --agent cursor` | preToolUse hook (hooks.json) |
 | **Gemini CLI** | `rtk init -g --gemini` | BeforeTool hook |
+| **Google Antigravity CLI (`agy`)** | `rtk init -g --agent agy` | PreToolUse hook — deny-with-reason (global) |
 | **Codex** | `rtk init -g --codex` | AGENTS.md + RTK.md instructions |
 | **Windsurf** | `rtk init --agent windsurf` | .windsurfrules (project-scoped) |
 | **Cline / Roo Code** | `rtk init --agent cline` | .clinerules (project-scoped) |
@@ -368,7 +370,7 @@ RTK supports 13 AI coding tools. Each integration rewrites shell commands to `rt
 | **Hermes** | `rtk init --agent hermes` | Python plugin adapter (terminal command mutation via `rtk rewrite`) |
 | **Mistral Vibe** | Planned ([#800](https://github.com/rtk-ai/rtk/issues/800)) | Blocked on upstream |
 | **Kilo Code** | `rtk init --agent kilocode` | .kilocode/rules/rtk-rules.md (project-scoped) |
-| **Google Antigravity** | `rtk init --agent antigravity` | .agents/rules/antigravity-rtk-rules.md (project-scoped) |
+| **Google Antigravity IDE** | `rtk init --agent antigravity` | .agents/rules/antigravity-rtk-rules.md (project-scoped) |
 
 For per-agent setup details, override controls, and graceful degradation, see the [Supported Agents guide](https://www.rtk-ai.app/guide/getting-started/supported-agents). The Hermes plugin source and tests live in `hooks/hermes/`; installed Hermes runtime files still live under `~/.hermes/plugins/rtk-rewrite/`.
 

hooks/antigravity/README.md

@@ -2,8 +2,85 @@
 
 > Part of [`hooks/`](../README.md) — see also [`src/hooks/`](../../src/hooks/README.md) for installation code
 
-## Specifics
+## Supported Modes
 
-- Prompt-level guidance only (no programmatic hook) -- relies on Antigravity reading custom instructions
-- `rules.md` contains the instruction to prefix all shell commands with `rtk`, usage examples, and meta commands
-- Installed to `.agents/rules/antigravity-rtk-rules.md` (project-local) by `rtk init --agent antigravity`
+RTK supports two separate Google Antigravity integrations:
+
+### 1. Antigravity CLI (`agy`) — Programmatic Hook
+
+The `agy` CLI (successor to Gemini CLI) supports a JSON hook protocol.  RTK registers as a `PreToolUse` hook that rewrites shell commands before execution.
+
+**Install (global only):**
+```bash
+rtk init -g --agent agy
+```
+
+agy CLI hook support is **global-only** — there is no project-local install. The hook runner is registered system-wide so it intercepts all agy sessions.
+
+**Files written:**
+- `~/.gemini/config/hooks.json` — registers the `PreToolUse` hook
+- `~/.gemini/antigravity-cli/settings.json` — grants `command(rtk)` permission
+
+**Hook entry written to `~/.gemini/config/hooks.json`:**
+```json
+{
+  "rtk-antigravity": {
+    "enabled": true,
+    "PreToolUse": [
+      {
+        "toolNameMatcher": "^(run_command|Bash|bash)$",
+        "hooks": [{"type": "command", "command": "/path/to/rtk hook antigravity"}]
+      }
+    ]
+  }
+}
+```
+
+**Hook protocol:**
+
+agy sends a JSON payload to stdin; the hook replies to stdout.
+
+Input (`run_command` tool):
+```json
+{"toolCall": {"name": "run_command", "args": {"CommandLine": "git status"}}}
+```
+
+Output — deny with replacement name (model retries with `rtk git status`, auto-approved via `command(rtk)` allow entry):
+```json
+{"denyReason": "RTK: use 'rtk git status' instead of 'git status' (60-90% token savings)"}
+```
+
+Input (`Bash` tool):
+```json
+{"toolCall": {"name": "Bash", "args": {"command": "cargo test"}}}
+```
+
+Non-shell tools and commands already prefixed with `rtk` receive `{"allowTool": true}` and pass through unchanged.
+
+> **Note:** agy's `overwrite` field in `PreToolHookResult` is silently ignored regardless of `toolPermission` mode. RTK uses the deny-and-retry pattern as a workaround until `overwrite` is implemented by agy.
+
+**Uninstall:**
+```bash
+rtk init -g --uninstall --agent agy
+```
+
+### 2. Antigravity IDE — Prompt-Level Guidance
+
+The Antigravity IDE (formerly "Antigravity") reads project rules files.  RTK installs its awareness instructions as a rules file.
+
+**Install (project-local only):**
+```bash
+rtk init --agent antigravity
+```
+
+- Installs `.agents/rules/antigravity-rtk-rules.md` in the project root
+- Instructs Antigravity to prefix shell commands with `rtk`
+- No programmatic hook — relies on the model following the rules
+
+## Gemini CLI (Legacy)
+
+The Gemini CLI is still supported but is now considered **legacy**.  New users should use `agy`.
+
+```bash
+rtk init -g --gemini    # Gemini CLI (legacy)
+```

src/cmds/system/json_cmd.rs

@@ -106,7 +106,8 @@ fn compact_json(value: &Value, depth: usize, max_depth: usize) -> String {
         Value::Number(n) => format!("{}{}", indent, n),
         Value::String(s) => {
             if s.len() > 80 {
-                let end = s.floor_char_boundary(77);
+                let mut end = 77.min(s.len());
+                while !s.is_char_boundary(end) { end -= 1; }
                 format!("{}\"{}...\"", indent, &s[..end])
             } else {
                 format!("{}\"{}\"", indent, s)

src/cmds/system/pipe_cmd.rs

@@ -140,9 +140,9 @@ fn find_wrapper(input: &str) -> String {
 }
 
 pub fn auto_detect_filter(input: &str) -> fn(&str) -> String {
-    let end = input.len().min(1024);
+    let mut end = input.len().min(1024);
     // Avoid panic: byte 1024 may fall inside a multi-byte UTF-8 char
-    let end = input.floor_char_boundary(end);
+    while !input.is_char_boundary(end) { end -= 1; }
     let first_1k = &input[..end];
 
     if first_1k.contains("test result:") && first_1k.contains("passed;") {

src/hooks/constants.rs

@@ -21,6 +21,13 @@ pub const OPENCODE_PLUGIN_FILE: &str = "rtk.ts";
 pub const CURSOR_DIR: &str = ".cursor";
 pub const CODEX_DIR: &str = ".codex";
 pub const GEMINI_DIR: &str = ".gemini";
+
+#[allow(dead_code)]
+pub const ANTIGRAVITY_DIR: &str = ".agents";
+
+/// Config subdirectory for the Antigravity CLI (agy) under ~/.gemini/
+pub const AGY_CLI_SUBDIR: &str = "antigravity-cli";
+
 pub const HERMES_DIR: &str = ".hermes";
 pub const HERMES_PLUGINS_SUBDIR: &str = "plugins";
 pub const HERMES_PLUGIN_NAME: &str = "rtk-rewrite";