After updates

db/schema.sql

@@ -115,6 +115,20 @@ CREATE TABLE IF NOT EXISTS scan_history (
     error_message TEXT DEFAULT NULL
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
 
+-- -----------------------------------------------------
+-- Table: scanner_lock
+-- Single-instance guard for the directory scanner. Ensures only one scan
+-- runs at a time across all replicas. A lease (locked_at + lease_seconds)
+-- lets a live scanner keep the lock via heartbeats, and lets a crashed
+-- scanner's lock be taken over once it goes stale.
+-- -----------------------------------------------------
+CREATE TABLE IF NOT EXISTS scanner_lock (
+    lock_name VARCHAR(64) PRIMARY KEY,
+    owner VARCHAR(128) NOT NULL COMMENT 'Instance id (host-pid-uuid) holding the lock',
+    locked_at DATETIME NOT NULL COMMENT 'Last time the lock was acquired or heartbeated',
+    lease_seconds INT NOT NULL DEFAULT 21600 COMMENT 'Lock is stale if older than this (6 hours)'
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
 -- -----------------------------------------------------
 -- Insert default model entry
 -- -----------------------------------------------------