feat: add Gemini CLI support via rtk init --gemini

[ousamabenyounes]

Summary

Replaces #174 (too many conflicts after upstream restructuring). Clean implementation on latest develop.

• rtk hook gemini: Native Rust hook processor for Gemini CLI BeforeTool hooks. Reads JSON from stdin, delegates to rewrite_command() (single source of truth — no duplicate rewrite logic), outputs Gemini-format JSON response.
• rtk init -g --gemini: Installs hook wrapper (~/.gemini/hooks/rtk-hook-gemini.sh), GEMINI.md, and patches ~/.gemini/settings.json.
• rtk init -g --gemini --uninstall: Clean removal of all Gemini artifacts.

Key design decisions

1. Reuses rewrite_command() from discover/registry.rs instead of duplicating rewrite rules (unlike the old PR). One source of truth for all hook engines.
2. Thin shell wrapper (exec rtk hook gemini) keeps the hook script minimal and testable — all logic is in Rust.
3. Additive only — no changes to existing Claude Code or OpenCode hooks. --gemini is a new opt-in flag.

Files changed

File	Change
src/hook_cmd.rs	New module — Gemini BeforeTool hook processor
src/main.rs	--gemini flag, Hook subcommand routing
src/init.rs	run_gemini(), patch_gemini_settings(), uninstall_gemini()
README.md	Gemini CLI section

Test plan

• cargo fmt --all --check — OK
• cargo clippy --all-targets — 0 new warnings
• cargo test — 905 passed, 3 ignored
• 6 unit tests in hook_cmd.rs covering hook format, rewrite delegation, env prefix, exclusions
• Manual: rtk init -g --gemini on a machine with Gemini CLI installed
• Manual: verify git status is rewritten in Gemini CLI session

Closes #174

🤖 Generated with Claude Code

[ousamabenyounes]

Live testing on Gemini CLI ✅

Tested on Gemini CLI 0.32.1 (Linux) — hook works end-to-end:

Setup:

rtk init -g --gemini --auto-patch
# → Hook: ~/.gemini/hooks/rtk-hook-gemini.sh
# → GEMINI.md installed
# → settings.json patched with BeforeTool hook

Result: Gemini types git status, hook rewrites to rtk git status — compact output returned:

┌─ Shell: rtk git status ──────────────────────────────────┐
│ 📌 feat-live-translate...origin/feat-live-translate      │
│ 📝 Modified: 1 files                                    │
│    Caddyfile                                             │
└──────────────────────────────────────────────────────────┘

3 lines instead of ~15 — standard RTK compression.

Hook processor verified with all command families:

Input	Rewritten	Status
git status	rtk git status	✅
cargo test	rtk cargo test	✅
RUST_LOG=debug cargo build	RUST_LOG=debug rtk cargo build	✅ env prefix preserved
rtk git log	passthrough (no double rewrite)	✅
echo hello	{"decision":"allow"} (no rewrite)	✅
non-shell tool (read_file)	{"decision":"allow"} (ignored)	✅

Install/uninstall cycle:

• rtk init -g --gemini --auto-patch → creates hook + GEMINI.md + patches settings.json ✅
• Re-run → idempotent (no duplicate hook entry) ✅
• rtk init -g --gemini --uninstall → removes all 3 artifacts cleanly ✅
• Re-install after uninstall → works correctly ✅