fix(model-fallback): enable by default and add missing error patterns for usage limits (#2393)

src/plugin/hooks/create-session-hooks.ts

@@ -153,7 +153,7 @@ export function createSessionHooks(args: {
 
   // Model fallback hook (configurable via model_fallback config + disabled_hooks)
   // This handles automatic model switching when model errors occur
-  const isModelFallbackConfigEnabled = pluginConfig.model_fallback ?? false
+  const isModelFallbackConfigEnabled = pluginConfig.model_fallback ?? true
   const modelFallback = isModelFallbackConfigEnabled && isHookEnabled("model-fallback")
     ? safeHook("model-fallback", () =>
       createModelFallbackHook({

src/shared/model-error-classifier.ts

@@ -55,9 +55,17 @@ const RETRYABLE_MESSAGE_PATTERNS = [
   "timeout",
   "service unavailable",
   "internal_server_error",
+  "free usage",
+  "usage exceeded",
+  "credit",
+  "balance",
+  "temporarily unavailable",
+  "try again",
   "503",
   "502",
   "504",
+  "429",
+  "529",
 ]
 
 const AUTO_RETRY_GATE_PATTERNS = [