fix(daemon): Antigravity adapter — stdin prompt, brand icon, form loop, empty-output guard

- Switch prompt delivery from argv to stdin (`agy -p -`) to avoid the
  30KB maxPromptArgBytes limit that blocked real-world composed prompts
- Add official Antigravity brand SVG icon to agent picker
- Fix repeated question-form loop for plain agents by injecting an
  OVERRIDE block when form answers are already present in the transcript
- Add empty-output guard for plain agents so expired auth or silent
  failures surface a user-visible error instead of a blank "Done" turn

apps/daemon/src/runtimes/defs/antigravity.ts

@@ -1,41 +1,16 @@
 import { DEFAULT_MODEL_OPTION } from './shared.js';
 import type { RuntimeAgentDef } from '../types.js';
 
-// Google Antigravity — agentic dev platform launched 2025-11 with Gemini 3.
-// `agy` is the terminal CLI surface; the IDE (Antigravity 2.0) shares the
-// same agent engine and OAuth credentials via the system keyring, so a
-// signed-in user is authenticated on first run with no extra work.
-//
-// As of v1.0.3 the CLI is TUI-first and minimally headless:
-//   - `agy -p "<prompt>"` runs a single non-interactive turn and prints
-//     the assistant reply as plain text to stdout, then exits.
-//   - There is no JSON / stream-json / ACP output mode yet (open upstream
-//     issues #119, #31), and no `--model` flag yet (open issue #35).
-//   - The prompt MUST go on argv as the value of `-p`; stdin piping is
-//     not supported (`-p` is a value flag, not a boolean).
-//
-// Until upstream ships a structured output mode, we expose Antigravity as
-// a `plain` runtime — single-turn text reply with no tool_use streaming
-// and no model picker. When `--output-format stream-json` lands we will
-// upgrade buildArgs + add a dedicated event parser.
 export const antigravityAgentDef = {
   id: 'antigravity',
   name: 'Antigravity',
   bin: 'agy',
   versionArgs: ['--version'],
-  // Only `default` for now: `agy` has no `--model` flag (upstream issue
-  // #35). Showing concrete model ids in the picker would mislead users
-  // into thinking the choice is wired through. Upgrade this list when
-  // upstream adds model selection.
   fallbackModels: [DEFAULT_MODEL_OPTION],
-  buildArgs: (prompt, _imagePaths, _extra = [], _options = {}) => {
-    return ['-p', prompt];
+  buildArgs: (_prompt, _imagePaths, _extra = [], _options = {}) => {
+    return ['-p', '-'];
   },
-  // Guard against prompts that would blow Windows' ~32 KB CreateProcess
-  // limit. Prompt rides on argv because `agy -p` is a value flag with
-  // no stdin sentinel; 30_000 bytes mirrors the deepseek budget and
-  // leaves ~2.7 KB of argv headroom for `-p` plus quoting.
-  maxPromptArgBytes: 30_000,
+  promptViaStdin: true,
   streamFormat: 'plain',
   installUrl: 'https://antigravity.google/cli',
   docsUrl: 'https://antigravity.google/docs/cli-overview',

apps/daemon/src/server.ts

@@ -2263,15 +2263,15 @@ function formAnswerTransitionForCurrentPrompt(currentPrompt) {
     '## Latest user turn - form answers submitted',
     trimmed,
     '',
-    `The user has answered the ${formId} form. Do not emit another ${formId} form.`,
+    `The user has answered the ${formId} form. Do NOT emit another <question-form> of any kind. The brief is locked.`,
   ];
-  if (formId.toLowerCase() === 'discovery') {
+  if (formId.toLowerCase() === 'discovery' || formId.toLowerCase() === 'task-type') {
     lines.push(
-      'Continue with RULE 2 / RULE 3 now. For Branch B answers, build now instead of asking another brief.',
+      'Continue with RULE 2 / RULE 3 now. For Branch B answers, build now instead of asking another brief. SKIP RULE 1 entirely — the form has already been answered.',
     );
   } else {
     lines.push(
-      'Treat these form answers as the active user turn instead of replaying the transcript as a fresh request.',
+      'Treat these form answers as the active user turn instead of replaying the transcript as a fresh request. Do NOT re-ask for information already provided.',
     );
   }
   return lines.join('\n');
@@ -10564,14 +10564,22 @@ export async function startServer({
     // instructions and request) — see server.ts:9920 composer notes.
     const ECHO_GUARD =
       '\n\n(Do not quote, restate, or echo the # Instructions block above in your reply. Begin your response with the answer to the # User request below.)';
+    const formAlreadyAnswered = FORM_ANSWERS_HEADER_RE.test(
+      typeof currentPrompt === 'string' ? currentPrompt : '',
+    );
+    const formOverride = formAlreadyAnswered
+      ? '## OVERRIDE — form already answered\nThe user has already submitted their form answers (see # User request below). Do NOT emit any `<question-form>` tag. RULE 1 does NOT apply — the discovery/task-type form is done. Proceed to RULE 2 / RULE 3 and build the artifact.\n\n'
+      : '';
     const composed = [
       instructionPrompt
-        ? `# Instructions (read first)\n\n${instructionPrompt}${cwdHint}${linkedDirsHint}${ECHO_GUARD}\n\n---\n`
+        ? `# Instructions (read first)\n\n${formOverride}${instructionPrompt}${cwdHint}${linkedDirsHint}${ECHO_GUARD}\n\n---\n`
         : cwdHint
-          ? `# Instructions${cwdHint}${linkedDirsHint}${ECHO_GUARD}\n\n---\n`
+          ? `# Instructions\n\n${formOverride}${cwdHint}${linkedDirsHint}${ECHO_GUARD}\n\n---\n`
           : linkedDirsHint
-            ? `# Instructions${linkedDirsHint}${ECHO_GUARD}\n\n---\n`
-            : '',
+            ? `# Instructions\n\n${formOverride}${linkedDirsHint}${ECHO_GUARD}\n\n---\n`
+            : formOverride
+              ? `# Instructions\n\n${formOverride}${ECHO_GUARD}\n\n---\n`
+              : '',
       `# User request\n\n${userRequestPrompt}${attachmentHint}${commentHint}`,
       safeImages.length
         ? `\n\n${safeImages.map((p) => `@${p}`).join(' ')}`
@@ -11538,15 +11546,9 @@ export async function startServer({
           return design.runs.finish(run, 'failed', code ?? 1, signal ?? null);
         }
       }
-      // Empty-output guard: a clean `code === 0` exit on a stream we are
-      // tracking, with no error frame and no substantive event, means the
-      // run silently finished without producing anything visible. That used
-      // to be marked `succeeded` and rendered as an empty assistant turn —
-      // see issue #691, where OpenCode runs were ending in ~3s with no
-      // chat content and no error banner. Surface an explicit failure
-      // instead so the chat shows a clear reason. ACP sessions and plain
-      // stdout streams are gated out via `trackingSubstantiveOutput`;
-      // their success/failure determination lives elsewhere.
+      // Empty-output guard: a clean `code === 0` exit with no visible
+      // output means the run silently finished without producing anything.
+      // Surface an explicit failure so the chat shows a clear reason.
       if (
         code === 0 &&
         !run.cancelRequested &&
@@ -11560,6 +11562,29 @@ export async function startServer({
         ));
         return design.runs.finish(run, 'failed', code, signal);
       }
+      // Plain-stream empty-output guard: plain agents send raw stdout
+      // chunks without structured event tracking. Detect auth failures
+      // or silent empty responses when exit 0 but no stdout was seen.
+      if (
+        code === 0 &&
+        !run.cancelRequested &&
+        !trackingSubstantiveOutput &&
+        !childStdoutSeen
+      ) {
+        const authFailure = classifyAgentAuthFailure(
+          agentId,
+          `${agentStderrTail}\n${agentStdoutTail}`,
+        );
+        const msg = authFailure
+          ? authFailure.message ?? `${def.name} authentication expired. Please re-authenticate and retry.`
+          : `${def.name} returned an empty response. This may indicate an expired session — try re-authenticating the agent.`;
+        send('error', createSseErrorPayload(
+          authFailure ? 'AGENT_AUTH_REQUIRED' : 'AGENT_EXECUTION_FAILED',
+          msg,
+          { retryable: true },
+        ));
+        return design.runs.finish(run, 'failed', 0, signal);
+      }
       // ACP agents that don't shut down on stdin.end() (e.g. Devin for
       // Terminal) are forced to exit via SIGTERM from attachAcpSession after
       // a clean prompt completion. Without an override, the chat run would

apps/daemon/tests/runtimes/agent-args.test.ts

@@ -451,40 +451,20 @@ test('qwen args check promptViaStdin, base args, model args and exclude `-` sent
 });
 
 // `agy` v1.0.3 takes the prompt as the value of `-p` (the flag is named
-// `--print` / `--prompt`, accepts a string, and rejects with `flag needs
-// an argument: -p` when omitted). There is no `--model` flag yet
-// (upstream issue #35), no stdin sentinel, and no JSON output mode
-// (issue #119) — the daemon ships antigravity as a `plain` runtime
-// until those land. Pin the argv shape so a future upstream redesign
-// (e.g. renaming `-p` back to a boolean, adding `--model`) surfaces
-// here and forces an explicit re-review of the integration.
-test('antigravity args put the prompt on argv as the value of -p', () => {
+test('antigravity pipes prompt via stdin with -p - sentinel', () => {
   assert.equal(antigravity.bin, 'agy');
   assert.equal(antigravity.streamFormat, 'plain');
-  assert.equal(antigravity.promptViaStdin, undefined);
+  assert.equal(antigravity.promptViaStdin, true);
 
   const args = antigravity.buildArgs('write hello world', [], [], {});
-  assert.deepEqual(args, ['-p', 'write hello world']);
+  assert.deepEqual(args, ['-p', '-']);
 
-  // No model flag — picking a model in the UI must not silently inject
-  // an unsupported `--model` arg that would fail with `flag provided
-  // but not defined`. Revisit when upstream ships issue #35.
   const withModel = antigravity.buildArgs('hi', [], [], { model: 'gemini-3-pro' });
   assert.equal(withModel.includes('--model'), false);
-  assert.deepEqual(withModel, ['-p', 'hi']);
+  assert.deepEqual(withModel, ['-p', '-']);
 
-  // Prompt rides on argv (no `-` stdin sentinel), so a maxPromptArgBytes
-  // budget must exist so the spawn pipeline can fail fast on oversized
-  // composed prompts before hitting CreateProcess/E2BIG.
-  assert.ok(
-    typeof antigravity.maxPromptArgBytes === 'number'
-      && antigravity.maxPromptArgBytes > 0
-      && antigravity.maxPromptArgBytes < 32_768,
-    `antigravity must declare maxPromptArgBytes under Windows' ~32 KB CreateProcess limit; got ${antigravity.maxPromptArgBytes}`,
-  );
+  assert.equal(antigravity.maxPromptArgBytes, undefined);
 
-  // Model picker must surface as "no real choice" until upstream wires
-  // `--model`. Only the synthetic default option ships.
   assert.deepEqual(
     antigravity.fallbackModels.map((m) => m.id),
     ['default'],

apps/web/public/agent-icons/antigravity.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="-2 -1 28 28"><path d="M21.751 22.607c1.34 1.005 3.35.335 1.508-1.508C17.73 15.74 18.904 1 12.037 1 5.17 1 6.342 15.74.815 21.1c-2.01 2.009.167 2.511 1.507 1.506 5.192-3.517 4.857-9.714 9.715-9.714 4.857 0 4.522 6.197 9.714 9.715z" fill="url(#ag)"/><defs><linearGradient id="ag" x1="2" y1="12" x2="22" y2="12" gradientUnits="userSpaceOnUse"><stop stop-color="#4285F4"/><stop offset=".33" stop-color="#EA4335"/><stop offset=".66" stop-color="#FBBC04"/><stop offset="1" stop-color="#34A853"/></linearGradient></defs></svg>

apps/web/src/components/AgentIcon.tsx

@@ -29,6 +29,7 @@ const ICON_EXT: Record<string, 'svg' | 'png'> = {
   kiro: 'svg',
   kilo: 'svg',
   vibe: 'svg',
+  antigravity: 'svg',
   aider: 'png',
   'trae-cli': 'png',
   devin: 'png',