@@ -61,7 +61,7 @@ const makeHarness = Effect.fn("makeAuthTestHarness")(function* (
   } = {},
 ) {
   const authenticated = yield* Deferred.make<void, AcpErrors.AcpError>();
-  const discovered = yield* Deferred.make<void>();
+  const discovered = yield* Deferred.make<void, AcpErrors.AcpError>();
   const closed = yield* Deferred.make<void>();
   const events: string[] = [];
   let receiveAuthorizationUrl:
@@ -224,6 +224,33 @@ it.layer(NodeServices.layer)("AntigravityAuth", (it) => {
     }),
   );
 
+  it.effect(
+    "distinguishes a post-authentication session failure without exposing its payload",
+    () =>
+      Effect.gen(function* () {
+        const harness = yield* makeHarness();
+        yield* harness.auth.controller.start(owner);
+        yield* phase(harness.auth, "waiting");
+        yield* Deferred.succeed(harness.authenticated, undefined);
+        yield* Deferred.fail(
+          harness.discovered,
+          new AcpErrors.AcpRequestError({
+            code: -32603,
+            errorMessage: `Internal error ${callbackUrl}`,
+            method: "session/new",
+          }),
+        );
+        const failed = yield* phase(harness.auth, "failed");
+        assert.equal(
+          failed.message,
+          "Antigravity authenticated, but could not initialize a session or load models.",
+        );
+        assert.isNull(failed.authorizationUrl);
+        assert.deepEqual(harness.catalog(), ["previous-account-model"]);
+        yield* Deferred.await(harness.closed);
+      }),
+  );
+
   it.effect("does not call callback HTTP success a successful Google sign-in", () =>
     Effect.gen(function* () {
       const harness = yield* makeHarness();
 
@@ -114,6 +114,9 @@ function safeAuthFailure(cause: Cause.Cause<unknown>, usesBrowser: boolean): str
       if (/access_denied|denied access|cancelled/i.test(error.value.errorMessage)) {
         return "Google sign-in was not approved. Start sign-in again.";
       }
+      if (error.value.method === "session/new" && error.value.code === -32603) {
+        return "Antigravity authenticated, but could not initialize a session or load models.";
+      }
       if (!usesBrowser && error.value.code === -32602) {
         return "Antigravity rejected the configured credentials. Check the provider settings.";
       }
Original file line number	Diff line number	Diff line change
`@@ -114,6 +114,9 @@ function safeAuthFailure(cause: Cause.Cause<unknown>, usesBrowser: boolean): str`
`114`	`114`	`if (/access_denied\|denied access\|cancelled/i.test(error.value.errorMessage)) {`
`115`	`115`	`return "Google sign-in was not approved. Start sign-in again.";`
`116`	`116`	`}`
	`117`	`+ if (error.value.method === "session/new" && error.value.code === -32603) {`
	`118`	`+ return "Antigravity authenticated, but could not initialize a session or load models.";`
	`119`	`+ }`
`117`	`120`	`if (!usesBrowser && error.value.code === -32602) {`
`118`	`121`	`return "Antigravity rejected the configured credentials. Check the provider settings.";`
`119`	`122`	`}`