diff --git a/scripts/deregister-room.ts b/scripts/deregister-room.ts
index ab2c3b2..0729930 100644
--- a/scripts/deregister-room.ts
+++ b/scripts/deregister-room.ts
@@ -4,7 +4,7 @@
  * channel record (chats) and its message history (messages).
  *
  * Usage:
- *   bun scripts/deregister-room.ts [--dry-run] [--force] <channelId|jid> [more...]
+ *   bun scripts/deregister-room.ts [--dry-run] [--force] [--no-backup] <channelId|jid> [more...]
  *
  * What it removes for each target chat:
  *   - room registration + role/skill overrides + channel owner lease
@@ -24,6 +24,8 @@
  *   - a group folder shared by another remaining room is NOT deleted on disk
  *     (only that chat's DB rows are removed)
  *   - --dry-run reports what would change without writing anything
+ *   - the DB is auto-backed up to /home/claude/ejclaw-db-backup-<ts>.db before
+ *     the purge unless --no-backup is passed
  */
 import { execFileSync } from 'child_process';
 import fs from 'fs';
@@ -36,11 +38,12 @@ import { DATA_DIR, GROUPS_DIR, STORE_DIR } from '../src/config.js';
 const args = process.argv.slice(2);
 const dryRun = args.includes('--dry-run');
 const force = args.includes('--force');
+const noBackup = args.includes('--no-backup');
 const ids = args.filter((a) => !a.startsWith('--'));
 
 if (ids.length === 0) {
   console.error(
-    'Usage: bun scripts/deregister-room.ts [--dry-run] [--force] <channelId|jid> [more...]',
+    'Usage: bun scripts/deregister-room.ts [--dry-run] [--force] [--no-backup] <channelId|jid> [more...]',
   );
   process.exit(2);
 }
@@ -126,6 +129,14 @@ const taskIds = (
   }>
 ).map((r) => r.id);
 const qT = taskIds.map(() => '?').join(',');
+// task_run_logs.task_id references scheduled_tasks.id (NOT paired_tasks.id), so
+// its rows must be pruned by the chat's scheduled task ids.
+const scheduledTaskIds = (
+  db
+    .query(`SELECT id FROM scheduled_tasks WHERE chat_jid IN (${qJ})`)
+    .all(...jids) as Array<{ id: string }>
+).map((r) => r.id);
+const qS = scheduledTaskIds.map(() => '?').join(',');
 const safeFolderList = [...safeFolders];
 const qF = safeFolderList.map(() => '?').join(',');
 
@@ -158,7 +169,17 @@ const addTask = (t: string) => {
 addTask('paired_turn_attempts');
 addTask('paired_turn_outputs');
 addTask('paired_turns');
-addTask('task_run_logs');
+// Prune scheduled-task run logs before the scheduled_tasks rows they belong to.
+if (scheduledTaskIds.length) {
+  plan.push({
+    table: 'task_run_logs',
+    n: count('task_run_logs', `task_id IN (${qS})`, scheduledTaskIds),
+    run: () =>
+      db
+        .query(`DELETE FROM task_run_logs WHERE task_id IN (${qS})`)
+        .run(...scheduledTaskIds),
+  });
+}
 for (const t of [
   'paired_task_execution_leases',
   'paired_turn_reservations',
@@ -222,6 +243,19 @@ if (dryRun) {
 }
 
 // --- execute ---
+// Auto-backup the DB before the irreversible purge (skip with --no-backup).
+if (!noBackup) {
+  const dbFile = path.join(STORE_DIR, 'messages.db');
+  const stamp = new Date()
+    .toISOString()
+    .replace(/[-:]/g, '')
+    .replace(/\..+$/, '')
+    .replace('T', '-');
+  const backup = path.join('/home/claude', `ejclaw-db-backup-${stamp}.db`);
+  fs.copyFileSync(dbFile, backup);
+  console.log(`DB backed up to ${backup}`);
+}
+
 db.exec('BEGIN');
 try {
   for (const p of plan) p.run();