Harden conversation replies and prioritize newest candidates

src/database/client.ts

@@ -336,6 +336,34 @@ export function runMigrations(db: Database.Database): void {
       addColumnIfNotExists(db, 'conversation_automation_claims', 'last_attempt_at', 'INTEGER');
       addColumnIfNotExists(db, 'conversation_automation_claims', 'attempt_count', 'INTEGER NOT NULL DEFAULT 0');
     },
+    () => db.exec(`
+      CREATE TABLE conversation_automation_claims_with_superseded (
+        account_id TEXT NOT NULL,
+        conversation_id TEXT NOT NULL,
+        incoming_key TEXT NOT NULL,
+        status TEXT NOT NULL CHECK(status IN ('pending', 'sent', 'superseded')),
+        claimed_at INTEGER NOT NULL,
+        sent_at INTEGER,
+        superseded_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_with_superseded (
+        account_id, conversation_id, incoming_key, status, claimed_at, sent_at,
+        reply_text, incoming_at, last_attempt_at, attempt_count
+      ) SELECT
+        account_id, conversation_id, incoming_key, status, claimed_at, sent_at,
+        reply_text, incoming_at, last_attempt_at, attempt_count
+      FROM conversation_automation_claims;
+      DROP TABLE conversation_automation_claims;
+      ALTER TABLE conversation_automation_claims_with_superseded RENAME TO conversation_automation_claims;
+      CREATE INDEX idx_conversation_automation_claims_status
+        ON conversation_automation_claims(account_id, status, claimed_at);
+    `),
   ];
 
   let currentVersion = db.pragma('user_version', { simple: true }) as number;