feat: add maxDelayMs setting to cap server-requested retry delays

When a provider (e.g., Google Gemini CLI) requests a retry delay longer
than maxDelayMs (default: 60s), the request fails immediately with an
informative error instead of waiting silently for hours.

The error is then handled by agent-level auto-retry, which shows the
delay to the user and allows aborting with Escape.

- Add maxRetryDelayMs to StreamOptions (packages/ai)
- Add maxRetryDelayMs to AgentOptions (packages/agent)
- Add retry.maxDelayMs to settings (packages/coding-agent)
- Update _isRetryableError to match 'retry delay' errors

fixes #1123

packages/coding-agent/src/core/agent-session.ts

@@ -1901,8 +1901,8 @@ export class AgentSession {
 		if (isContextOverflow(message, contextWindow)) return false;
 
 		const err = message.errorMessage;
-		// Match: overloaded_error, rate limit, 429, 500, 502, 503, 504, service unavailable, connection errors, fetch failed, terminated
-		return /overloaded|rate.?limit|too many requests|429|500|502|503|504|service.?unavailable|server error|internal error|connection.?error|connection.?refused|other side closed|fetch failed|upstream.?connect|reset before headers|terminated/i.test(
+		// Match: overloaded_error, rate limit, 429, 500, 502, 503, 504, service unavailable, connection errors, fetch failed, terminated, retry delay exceeded
+		return /overloaded|rate.?limit|too many requests|429|500|502|503|504|service.?unavailable|server error|internal error|connection.?error|connection.?refused|other side closed|fetch failed|upstream.?connect|reset before headers|terminated|retry delay/i.test(
 			err,
 		);
 	}