Harden conversation replies and prioritize newest candidates

tests/database.test.ts

@@ -160,7 +160,7 @@ describe('Database Client', () => {
         DROP TABLE conversation_automation_claims;
         DROP TABLE ai_usage;
       `);
-      db.pragma(`user_version = ${latestVersion - 5}`);
+      db.pragma(`user_version = ${latestVersion - 6}`);
       runMigrations(db);
 
       expect(db.prepare('SELECT recipient, reason FROM recipient_suppressions ORDER BY recipient COLLATE NOCASE').all())
@@ -170,6 +170,46 @@ describe('Database Client', () => {
         ]);
     });
 
+    it('preserves pending reply claims when adding auditable superseded status', () => {
+      runMigrations(db);
+      const latestVersion = db.pragma('user_version', { simple: true }) as number;
+      db.exec(`
+        DROP TABLE conversation_automation_claims;
+        CREATE TABLE conversation_automation_claims (
+          account_id TEXT NOT NULL,
+          conversation_id TEXT NOT NULL,
+          incoming_key TEXT NOT NULL,
+          status TEXT NOT NULL CHECK(status IN ('pending', 'sent')),
+          claimed_at INTEGER NOT NULL,
+          sent_at INTEGER,
+          reply_text TEXT,
+          incoming_at INTEGER,
+          last_attempt_at INTEGER,
+          attempt_count INTEGER NOT NULL DEFAULT 0,
+          PRIMARY KEY (account_id, conversation_id, incoming_key),
+          FOREIGN KEY (account_id) REFERENCES reddit_accounts(account_id) ON DELETE CASCADE
+        );
+        INSERT INTO conversation_automation_claims (
+          account_id, conversation_id, incoming_key, status, claimed_at,
+          reply_text, incoming_at, last_attempt_at, attempt_count
+        ) VALUES (
+          '__legacy_unassigned__', 'room', 'event', 'pending', 10,
+          'durable reply', 5, 11, 1
+        );
+      `);
+      db.pragma(`user_version = ${latestVersion - 1}`);
+
+      runMigrations(db);
+
+      expect(db.prepare(`
+        SELECT status, reply_text, incoming_at, last_attempt_at, attempt_count, superseded_at
+        FROM conversation_automation_claims
+      `).get()).toEqual({
+        status: 'pending', reply_text: 'durable reply', incoming_at: 5,
+        last_attempt_at: 11, attempt_count: 1, superseded_at: null,
+      });
+    });
+
     it('processed_posts has correct schema', () => {
       runMigrations(db);
       const columns = db.prepare('PRAGMA table_info(processed_posts)').all() as { name: string; notnull: number }[];