fix(antigravity): passthrough tab-autocomplete + mark default agent slot mandatory

MODEL_NO_MAP guard never re-routes Antigravity tab-autocomplete (tab_* models)
so latency-critical inline completion stays native. Flags gemini-3.5-flash-low
(agent/Default) as mandatory in the dashboard.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/unit/antigravity-mitm.test.js

@@ -0,0 +1,40 @@
+import { describe, expect, it } from "vitest";
+import { createRequire } from "module";
+import { MITM_TOOLS } from "../../src/shared/constants/cliTools.js";
+
+// config.js is the CJS MITM bundle module (dependency-isolated for the runtime copy).
+const require = createRequire(import.meta.url);
+const { MODEL_NO_MAP } = require("../../src/mitm/config.js");
+
+// All assertions below are grounded in a live MITM dump capture of Antigravity's
+// streamGenerateContent requests (see AI_JOURNAL): the agent loop sends
+// `gemini-3.5-flash-low`, tab-autocomplete sends `tab_jump_flash_lite_preview` /
+// `tab_flash_lite_preview`.
+describe("Antigravity MITM model handling", () => {
+  const ag = MITM_TOOLS.antigravity;
+
+  it("flags the out-of-box agent/Default model mandatory", () => {
+    expect(ag.defaultModels.find((m) => m.id === "gemini-3.5-flash-low")?.mandatory).toBe(true);
+  });
+
+  it("leaves models not proven auto-sent optional", () => {
+    for (const id of ["gemini-3-flash-agent", "gemini-3.1-pro-low", "claude-sonnet-4-6", "gpt-oss-120b-medium"]) {
+      expect(ag.defaultModels.find((m) => m.id === id)?.mandatory).toBeFalsy();
+    }
+  });
+
+  // Tab-autocomplete is latency-critical inline completion — it must passthrough natively,
+  // never get re-routed onto a chat-model mapping by the broad `flash` pattern.
+  it.each(["tab_jump_flash_lite_preview", "tab_flash_lite_preview"])(
+    "excludes tab-autocomplete model '%s' from re-routing",
+    (id) => {
+      expect((MODEL_NO_MAP.antigravity || []).some((re) => re.test(id))).toBe(true);
+    }
+  );
+
+  it("does not exclude real agent models from re-routing", () => {
+    for (const id of ["gemini-3.5-flash-low", "gemini-3-flash-agent", "claude-sonnet-4-6"]) {
+      expect((MODEL_NO_MAP.antigravity || []).some((re) => re.test(id))).toBe(false);
+    }
+  });
+});