fix(antigravity): add fail-fast on 429 rate limit

When Antigravity returns 429, throw immediately instead of waiting for the
server-provided retry delay (which can be 10+ minutes). This lets clawdbot
quickly rotate to another account.

This patch was previously in PR #454 but was accidentally removed in 0dbb569
when bumping to pi-ai 0.40.0. The upstream release did NOT include this fix.

Context: Antigravity rate limits cause pi-ai to sleep for the full retry
delay inside the request, blocking the thread. Clawdbot's timeout would
eventually fire, but waiting 10+ minutes is unacceptable UX.

Bundled with the empty error message filter since both handle 429 recovery.

patches/@mariozechner__pi-ai.patch

@@ -0,0 +1,18 @@
+diff --git a/dist/providers/google-gemini-cli.js b/dist/providers/google-gemini-cli.js
+index 0000000..1111111 100644
+--- a/dist/providers/google-gemini-cli.js
++++ b/dist/providers/google-gemini-cli.js
+@@ -248,6 +248,13 @@ async function* streamGeminiCli(model, context, credentials, options) {
+                         break; // Success, exit retry loop
+                     }
+                     const errorText = await response.text();
++                    // PATCH: Fail immediately on 429 to let caller rotate accounts
++                    // Antigravity rate limits can have very long retry delays (10+ minutes).
++                    // Instead of waiting, throw immediately so clawdbot can rotate to another account.
++                    if (response.status === 429) {
++                        console.log(`[pi-ai] 429 rate limit - failing fast to rotate account`);
++                        throw new Error(`Cloud Code Assist API error (${response.status}): ${errorText}`);
++                    }
+                     // Check if retryable
+                     if (attempt < MAX_RETRIES && isRetryableError(response.status, errorText)) {
+                         // Use server-provided delay or exponential backoff