fix: resolve 5 deployment blockers (runtime-fallback race, hashline legacy, tmux spawn, db open)

- runtime-fallback: guard session.error with sessionRetryInFlight to prevent
  double-advance during active retry; expand session.stop abort to include
  sessionAwaitingFallbackResult; remove premature pendingFallbackModel clearing
  from auto-retry finally block
- hashline-edit: add HASHLINE_LEGACY_REF_PATTERN for backward-compatible
  LINE:HEX dual-parse in parseLineRef and normalizeLineRef
- tmux-subagent: defer session on null queryWindowState; unconditionally
  re-queue deferred session on spawn failure (not just close+spawn)
- ultrawork-db: wrap new Database(dbPath) in try/catch to handle corrupted DB
- event: add try/catch guards around model-fallback logic in message.updated,
  session.status, and session.error handlers

src/plugin/ultrawork-db-model-override.ts

@@ -120,7 +120,17 @@ export function scheduleDeferredModelOverride(
       return
     }
 
-    const db = new Database(dbPath)
+    let db: InstanceType<typeof Database>
+    try {
+      db = new Database(dbPath)
+    } catch (error) {
+      log("[ultrawork-db-override] Failed to open DB, skipping deferred override", {
+        messageId,
+        error: String(error),
+      })
+      return
+    }
+
     try {
       retryViaMicrotask(db, messageId, targetModel, variant, 0)
     } catch (error) {