fix: add universal billing error detection for router mode

- Add HTTP 402 and 'insufficient credits' patterns to error classification
- Detect provider billing errors in both exception and message content paths

src/ai/message-handlers.ts

@@ -60,12 +60,15 @@ export function detectApiError(content: string): ApiErrorDetection {
   // When Claude Code hits its spending cap, it returns a short message like
   // "Spending cap reached resets 8am" instead of throwing an error.
   // These should retry with 5-30 min backoff so workflows can recover when cap resets.
+  // Also catches provider billing errors (OpenRouter 402, etc.) that appear in message content.
   const BILLING_PATTERNS = [
     'spending cap',
     'spending limit',
     'cap reached',
     'budget exceeded',
     'usage limit',
+    '402',                  // HTTP Payment Required (universal)
+    'insufficient credits', // OpenRouter
   ];
 
   const isBillingError = BILLING_PATTERNS.some((pattern) =>

src/error-handling.ts

@@ -211,7 +211,9 @@ export function classifyErrorForTemporal(error: unknown): TemporalErrorClassific
   // === BILLING ERRORS (Retryable with long backoff) ===
   // Anthropic returns billing as 400 invalid_request_error
   // Human can add credits OR wait for spending cap to reset (5-30 min backoff)
+  // 402 is HTTP "Payment Required" - universal across providers (OpenRouter, etc.)
   if (
+    message.includes('402') ||
     message.includes('billing_error') ||
     message.includes('credit balance is too low') ||
     message.includes('insufficient credits') ||