diff --git a/apps/server/src/provider/AntigravityInstallation.test.ts b/apps/server/src/provider/AntigravityInstallation.test.ts
index 0528cb4972c9..8d56f1980580 100644
--- a/apps/server/src/provider/AntigravityInstallation.test.ts
+++ b/apps/server/src/provider/AntigravityInstallation.test.ts
@@ -761,6 +761,34 @@ it.layer(NodeServices.layer)("Antigravity installation", (it) => {
       }),
   );
 
+  it.effect.skipIf(HostProcessPlatform.defaultValue() === "win32")(
+    "names the Antigravity CLI when only the CLI is on PATH",
+    () =>
+      Effect.gen(function* () {
+        const fs = yield* FileSystem.FileSystem;
+        const path = yield* Path.Path;
+        const baseDir = yield* fs.makeTempDirectoryScoped({ prefix: "t3-agy-cli-test-" });
+        const cliDirectory = path.join(baseDir, "cli");
+        const emptyDirectory = path.join(baseDir, "empty");
+        yield* fs.makeDirectory(cliDirectory);
+        yield* fs.makeDirectory(emptyDirectory);
+        yield* fs.writeFileString(path.join(cliDirectory, "agy"), "cli", { mode: 0o755 });
+        const { installation } = yield* makeHarness({ baseDir });
+        expect(
+          yield* installation.resolve(undefined, { PATH: emptyDirectory }).pipe(Effect.flip),
+        ).toMatchObject({
+          detail:
+            "Antigravity is not installed. Install it in this environment or set a custom executable path.",
+        });
+        expect(
+          yield* installation.resolve(undefined, { PATH: cliDirectory }).pipe(Effect.flip),
+        ).toMatchObject({
+          detail:
+            "The Antigravity CLI is installed, but T3 Code runs the separate Antigravity ACP agent. Install it in this environment or set a custom executable path.",
+        });
+      }),
+  );
+
   it.effect("keeps leased releases available while new sessions resolve the new release", () =>
     Effect.gen(function* () {
       const { installation, fs, stagingReleased } = yield* makeHarness({ previous: true });
diff --git a/apps/server/src/provider/AntigravityInstallation.ts b/apps/server/src/provider/AntigravityInstallation.ts
index ebcbd496ee3e..c40b2ffa49bd 100644
--- a/apps/server/src/provider/AntigravityInstallation.ts
+++ b/apps/server/src/provider/AntigravityInstallation.ts
@@ -6,6 +6,7 @@ import {
   HostProcessEnvironment,
   HostProcessPlatform,
 } from "@t3tools/shared/hostProcess";
+import { isCommandAvailable } from "@t3tools/shared/shell";
 import * as Clock from "effect/Clock";
 import * as Cause from "effect/Cause";
 import * as Context from "effect/Context";
@@ -400,6 +401,13 @@ export const makeAntigravityInstallation = Effect.fn("AntigravityInstallation.ma
       .map((directory) => path.resolve(directory, binary));
   };
 
+  const cliOnPath = (processEnvironment = environment) =>
+    isCommandAvailable("agy", { env: processEnvironment }).pipe(
+      Effect.provideService(HostProcessPlatform, platform),
+      Effect.provideService(FileSystem.FileSystem, fs),
+      Effect.provideService(Path.Path, path),
+    );
+
   const resolve: AntigravityInstallationService["resolve"] = Effect.fn(
     "AntigravityInstallation.resolve",
   )(
@@ -427,6 +435,12 @@ export const makeAntigravityInstallation = Effect.fn("AntigravityInstallation.ma
         const selected = yield* fromExternal(candidate, "path");
         if (selected) return selected;
       }
+      if (releaseAsset && (yield* cliOnPath(processEnvironment))) {
+        return yield* installationError(
+          "resolve",
+          "The Antigravity CLI is installed, but T3 Code runs the separate Antigravity ACP agent. Install it in this environment or set a custom executable path.",
+        );
+      }
       return yield* installationError(
         "resolve",
         releaseAsset