Add durable candidate funnel

src/database/client.ts

@@ -276,6 +276,42 @@ export function runMigrations(db: Database.Database): void {
     () => {
       addColumnIfNotExists(db, 'processed_posts', 'post_created_at', 'INTEGER');
     },
+    () => db.exec(`
+      CREATE TABLE IF NOT EXISTS candidate_queue (
+        post_id TEXT PRIMARY KEY,
+        subreddit TEXT NOT NULL,
+        author TEXT NOT NULL COLLATE NOCASE,
+        source_type TEXT NOT NULL CHECK(source_type IN ('image', 'chat')),
+        payload_json TEXT NOT NULL,
+        prepared_json TEXT,
+        post_created_at INTEGER NOT NULL,
+        priority REAL NOT NULL DEFAULT 1,
+        status TEXT NOT NULL CHECK(status IN (
+          'discovered', 'screening', 'ready', 'sending', 'retryable', 'sent', 'rejected'
+        )),
+        discovered_at INTEGER NOT NULL,
+        updated_at INTEGER NOT NULL,
+        available_at INTEGER NOT NULL,
+        lease_owner TEXT,
+        lease_expires_at INTEGER,
+        assigned_account_id TEXT,
+        attempt_count INTEGER NOT NULL DEFAULT 0,
+        last_error TEXT,
+        FOREIGN KEY (assigned_account_id) REFERENCES reddit_accounts(account_id) ON DELETE SET NULL
+      );
+      CREATE INDEX IF NOT EXISTS idx_candidate_queue_claim
+        ON candidate_queue(status, available_at, priority DESC, post_created_at DESC);
+      CREATE INDEX IF NOT EXISTS idx_candidate_queue_author
+        ON candidate_queue(author COLLATE NOCASE, status);
+      CREATE INDEX IF NOT EXISTS idx_candidate_queue_updated
+        ON candidate_queue(updated_at DESC);
+
+      CREATE TABLE IF NOT EXISTS runtime_state (
+        id INTEGER PRIMARY KEY CHECK(id = 1),
+        bot_running INTEGER NOT NULL CHECK(bot_running IN (0, 1)),
+        updated_at INTEGER NOT NULL
+      );
+    `),
   ];
 
   let currentVersion = db.pragma('user_version', { simple: true }) as number;