feat(gateway): recognise Antigravity CLI requests as antigravity-cli

[fylorn]

Requested by F · project thread

What this changes

Requests from Antigravity CLI (agy) now get client_hint = "antigravity-cli", the client id ThinkWatch Lite uses for it (ThinkWatch-Lite#213). Before, they got no hint, so Lite's "in use" indicator could never light up for agy.

Why

agy has no user agent of its own. Pointed at a custom Gemini endpoint, it sends the Go genai SDK default in both User-Agent and X-Goog-Api-Client:

google-genai-sdk/1.71.0 gl-go/go1.28-20260721-RC03 cl/951519500 +3ebc191975 X:fieldtrack,boringcrypto,simd,mapsplitgroup

Matching google-genai-sdk alone would label every Go program built on the SDK as agy, and hint.rs already prefers no guess to a wrong one. What sets agy apart is the Google-internal Go toolchain version after gl-go/ (it carries cl/<number>); a program built with a public Go release sends gl-go/go1.25.1. The hint matches all three: google-genai-sdk/ prefix, gl-go/, cl/.

How it was verified

• Downloaded agy 1.2.11 for linux-x64 from storage.googleapis.com/antigravity-public (the URL in Homebrew's antigravity-cli cask; sha256 matches the cask). Ran agy -p "say pong" with an isolated HOME, settings.json = {"modelProvider":"gemini"}, GOOGLE_GEMINI_BASE_URL=http://127.0.0.1:18999, GEMINI_API_KEY=<fake>, auto-update off and every proxy variable pointed at a dead port. No account was signed in. A local fake server logged two requests (gemini-3.1-flash-lite-preview for the title, gemini-3.1-pro-preview for the turn), both with the header above; nothing else distinguishing was sent (X-Goog-Api-Key, Content-Type, Accept-Encoding only).
• New test antigravity_cli_is_recognised_by_the_toolchain_in_its_user_agent uses the captured string verbatim, and asserts a public-toolchain Go SDK UA stays None. All 7 hint tests pass.
• cargo fmt --all -- --check, cargo clippy --workspace --all-targets -- -D warnings (rustc 1.98.1), cargo test --workspace: clean. ./scripts/smoke.sh: 60 passed, 0 failed.
• Only the display hint changes; it is never used for auth or routing, and no credential path is touched. CONTROL_API_VERSION is unchanged.

Notes for review

• The match depends on Google building agy with its internal toolchain. Only 1.2.11 could be checked (older builds were not reachable from here). If a future release switches to a public Go toolchain, the hint quietly goes back to None rather than guessing.
• Another Google-internal Go binary talking the Gemini API through the gateway (for example the Antigravity IDE's language server, if it ever supports a custom endpoint) would also be labelled antigravity-cli.

🤖 Generated with Claude Code

https://claude.ai/code/session_012JfMJSMbfEW5nzkn9vro9A

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Generated by Claude Code