fix(oauth+errors): OAuth silent refresh, quota STOP patterns, compaction loop cap

Bug fixes:
1. OAuth token refresh (#3149): buildHttpRequestInit() now attempts silent refresh
   via refresh_token before triggering full browser re-auth. Added refresh() method
   to McpOAuthProvider. Includes test isolation fix for discovery mock.

2. Quota error STOP (#3126): Added STOP_MESSAGE_PATTERNS in model-error-classifier
   that take precedence over RETRYABLE_MESSAGE_PATTERNS. Message-only quota errors
   now non-retryable. Runtime-fallback: quota_exceeded with 'retrying in' signal
   still triggers fallback (provider-managed auto-retry). Restored removed patterns.

3. Compaction loop (#3127): MAX_RECOVERY_ATTEMPTS=3 cap + additional suppression
   guard from opencode session in degradation monitor.

Also: refactored extractAutoRetrySignal to auto-retry-signal.ts, new regression
tests for quota classifier and compaction degradation monitor.

src/shared/model-error-classifier.ts

@@ -84,23 +84,25 @@ const STOP_MESSAGE_PATTERNS = [
   "usage limit has been reached",
   "free usage limit",
   "billing limit",
+  "billing hard limit",
   "monthly limit",
   "plan limit",
+  "subscription quota",
   "subscription limit",
+  "payment required",
   "out of credits",
   "credits exhausted",
   "insufficient credits",
   "insufficient balance",
+  "credit balance",
+  "usage limit for this month",
+  "exhausted your capacity",
 ]
 
 const AUTO_RETRY_GATE_PATTERNS = [
   "rate limit",
-  "quota",
-  "usage limit",
-  "limit reached",
   "cooling down",
   "credentials for model",
-  "exhausted your capacity",
 ]
 
 function hasProviderAutoRetrySignal(message: string): boolean {