feat(core): increase thought signature retry resilience

maxAttempts 2→3, initialDelayMs 500→1000 for "thought signature
chunk" errors to better handle transient API flakes.

packages/core/src/core/geminiChat.test.ts

@@ -1315,11 +1315,11 @@ describe('GeminiChat', () => {
         }
       }).rejects.toThrow(InvalidStreamError);
 
-      // Should be called 2 times (initial + 1 retry)
+      // Should be called 3 times (initial + 2 retries)
       expect(mockContentGenerator.generateContentStream).toHaveBeenCalledTimes(
-        2,
+        3,
       );
-      expect(mockLogContentRetry).toHaveBeenCalledTimes(1);
+      expect(mockLogContentRetry).toHaveBeenCalledTimes(2);
       expect(mockLogContentRetryFailure).toHaveBeenCalledTimes(1);
 
       // History should still contain the user message.

packages/core/src/core/geminiChat.ts

@@ -86,8 +86,8 @@ interface ContentRetryOptions {
 }
 
 const INVALID_CONTENT_RETRY_OPTIONS: ContentRetryOptions = {
-  maxAttempts: 2, // 1 initial call + 1 retry
-  initialDelayMs: 500,
+  maxAttempts: 3, // 1 initial call + 2 retries
+  initialDelayMs: 1000,
 };
 
 export const SYNTHETIC_THOUGHT_SIGNATURE = 'skip_thought_signature_validator';