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+# Adding Antigravity as an agent — research notes (not ready to merge)
+
+Status: **stub / research capture only**. No catalogue entry has been added to
+`agents.ts` yet. This file exists so the investigation isn't lost while we wait
+on input from whoever requested this — see "Open questions" below.
+
+## Why this might be worth doing
+
+`agents.ts`'s own doc comment says adding an agent is meant to be cheap:
+
+> Adding an eighth agent should be one entry here and nothing else.
+
+"Antigravity" is Google's agentic coding IDE (built by the ex-Windsurf team,
+now at Google; GA'd ~Nov 2025). It isn't in the catalogue today. It's plausibly
+in scope for the same reason Gemini CLI is.
+
+## The complication: "Antigravity" names two different things
+
+### 1. Antigravity CLI — looks straightforward
+
+Per its docs (`antigravity.google/docs/cli/install`):
+
+- `GOOGLE_GEMINI_BASE_URL` redirects model traffic to a custom endpoint — the
+  **same env var already used** by this tool's existing `gemini` → `api-key`
+  provider.
+- API-key auth is selected via `~/.gemini/antigravity-cli/settings.json`
+  (`modelProvider: gemini`), with the credential in `GEMINI_API_KEY`.
+  `GOOGLE_API_KEY` and `.env` are explicitly ignored.
+- Account-based login is a separate mode (session-based, `/logout` clears it);
+  unclear whether it honors the same base URL override.
+
+If this holds up under a real test, adding it is close to copy-pasting the
+existing `gemini` → `api-key` provider entry with a new host/label.
+
+### 2. Antigravity IDE — unverified, possibly not proxyable at all
+
+Community reverse-engineering (an archived, non-functional proxy project,
+`elad12390/antigravity-proxy`) reports:
+
+- Real traffic goes to an *internal* Cloud Code endpoint, e.g.
+  `https://daily-cloudcode-pa.sandbox.googleapis.com/v1internal:streamGenerateContent?alt=sse`
+  — architecturally the same family as the existing Gemini CLI "Google login"
+  route (`cloudcode-pa.googleapis.com`), which suggests the existing `gemini`
+  renderer in `render.ts` would likely parse the payload shape correctly
+  *if* we could see it.
+- But the author reports that plain env-var / MITM / DNS-based redirection did
+  **not** work — they describe "a complex handshake followed by socket/TLS-based
+  communication" that resisted interception, and archived the project as
+  non-functional.
+- This is second-hand, from one archived repo, and could be stale by the time
+  anyone reads this. It has not been independently verified against a live
+  install.
+- The IDE also lets the user pick the underlying model (Gemini 3 Pro or Claude
+  Sonnet 4.5 have both been reported). A Claude-backed session would need a
+  second provider row using the `anthropic` renderer, the same way Pi and
+  OpenCode already have multiple provider entries per backend.
+
+If the IDE genuinely can't be redirected, the right shape is a `reason`-only
+refusal entry next to Cursor and Amp — but with an honest, distinct reason
+(connection-level lock, not "prompt built server-side"), since the underlying
+cause looks different even though the practical outcome (nothing to log) is
+the same.
+
+## What confirming this needs
+
+Nobody on this has hands-on access to a live Antigravity install yet. To turn
+this from research into a real catalogue entry, someone needs to:
+
+1. Set `GOOGLE_GEMINI_BASE_URL=http://localhost:8787` (CLI) and/or
+   `CODE_ASSIST_ENDPOINT=http://localhost:8787` (IDE, by analogy with the
+   Gemini CLI login route) against a running `npm run request-logger`, and
+   report whether anything lands in `request-logger/logs/`.
+2. If something lands: paste one captured `.md` in this PR (or attach the raw
+   `.request.txt`) so the renderer/host/suffix can be pinned down for real,
+   the way every other entry in `agents.ts` has a test backing its suffix.
+3. If nothing lands: confirm which redirection knobs were tried, so the
+   refusal reason can be written accurately instead of guessed.
+
+## Open questions for the reporter
+
+- Did you mean the **Antigravity IDE** (the editor) or the **Antigravity
+  CLI**? They behave very differently for this tool's purposes.
+- Have you gotten Antigravity to route through *any* custom base URL or local
+  proxy successfully? If so, which setting worked, and what host/path did the
+  traffic actually hit?
+- Which model were you running it against (Gemini 3 Pro, Claude Sonnet 4.5,
+  something else)? That decides whether one provider row is enough or two are
+  needed.
+- Do you already have a captured request (even a manual curl/mitmproxy dump)
+  we could use as a fixture, instead of reverse-engineering from scratch?
+
+## Sources
+
+- https://antigravity.google/docs/cli/install
+- https://github.com/elad12390/antigravity-proxy (archived, reports interception failure against the IDE)
+- https://github.com/frieser/antigravity-proxy
+- https://github.com/alii13/Antigravity-cursor-proxy (different direction — bridges Antigravity's session *into* Cursor, not useful here directly)
+- https://www.datacamp.com/tutorial/antigravity-cli