fix: add optimistic reset for transient 429 rate limit errors

Fixes issue #71 - 'No accounts available' error when API returns 429

The Google Cloud Code API can return 429 RESOURCE_EXHAUSTED errors even
when accounts have quota available due to:
- Temporary API load/throttling
- Per-minute request limits (not per-day quota)
- Transient backend issues

This fix adds:
1. A 500ms buffer after waiting for rate limits to expire
2. Optimistic rate limit reset when all accounts appear stuck
3. Retry logic that clears rate limits and tries again

The fix works in conjunction with the server-level optimistic reset
that already exists, providing multiple layers of protection against
false 'No accounts available' errors.

Co-Authored-By: Claude <noreply@anthropic.com>

src/cloudcode/message-handler.js

@@ -72,8 +72,19 @@ export async function sendMessage(anthropicRequest, accountManager, fallbackEnab
                 const accountCount = accountManager.getAccountCount();
                 logger.warn(`[CloudCode] All ${accountCount} account(s) rate-limited. Waiting ${formatDuration(allWaitMs)}...`);
                 await sleep(allWaitMs);
+
+                // Add small buffer after waiting to ensure rate limits have truly expired
+                await sleep(500);
                 accountManager.clearExpiredLimits();
                 account = accountManager.pickNext(model);
+
+                // If still no account after waiting, try optimistic reset
+                // This handles cases where the API rate limit is transient
+                if (!account) {
+                    logger.warn('[CloudCode] No account available after wait, attempting optimistic reset...');
+                    accountManager.resetAllRateLimits();
+                    account = accountManager.pickNext(model);
+                }
             }
 
             if (!account) {

src/cloudcode/streaming-handler.js

@@ -71,8 +71,19 @@ export async function* sendMessageStream(anthropicRequest, accountManager, fallb
                 const accountCount = accountManager.getAccountCount();
                 logger.warn(`[CloudCode] All ${accountCount} account(s) rate-limited. Waiting ${formatDuration(allWaitMs)}...`);
                 await sleep(allWaitMs);
+
+                // Add small buffer after waiting to ensure rate limits have truly expired
+                await sleep(500);
                 accountManager.clearExpiredLimits();
                 account = accountManager.pickNext(model);
+
+                // If still no account after waiting, try optimistic reset
+                // This handles cases where the API rate limit is transient
+                if (!account) {
+                    logger.warn('[CloudCode] No account available after wait, attempting optimistic reset...');
+                    accountManager.resetAllRateLimits();
+                    account = accountManager.pickNext(model);
+                }
             }
 
             if (!account) {