diff --git a/services/mam-api/src/routes/sequences.js b/services/mam-api/src/routes/sequences.js
index 6f41189..97fc0bf 100644
--- a/services/mam-api/src/routes/sequences.js
+++ b/services/mam-api/src/routes/sequences.js
@@ -146,13 +146,30 @@ router.put('/:id', async (req, res, next) => {
 // ── DELETE /:id ───────────────────────────────────────────────────────────────
 router.delete('/:id', async (req, res, next) => {
   try {
-    await pool.query(`DELETE FROM sequences WHERE id = $1`, [req.params.id]);
+    const r = await pool.query(`DELETE FROM sequences WHERE id = $1`, [req.params.id]);
+    if (!r.rowCount) return res.status(404).json({ error: 'Sequence not found' });
     res.json({ ok: true });
   } catch (e) { next(e); }
 });
 
 // ── PUT /:id/clips – full replace of clip array (single transaction) ──────────
 router.put('/:id/clips', async (req, res, next) => {
+  // Verify sequence exists first (before acquiring transaction client)
+  const seqCheck = await pool.query(`SELECT id FROM sequences WHERE id = $1`, [req.params.id]);
+  if (!seqCheck.rows.length) return res.status(404).json({ error: 'Sequence not found' });
+
+  const clips = Array.isArray(req.body) ? req.body : [];
+  for (const c of clips) {
+    if (!c.asset_id) return res.status(400).json({ error: 'Each clip must have asset_id' });
+    if (!Number.isFinite(Number(c.timeline_in_frames)) || !Number.isFinite(Number(c.timeline_out_frames)) ||
+        !Number.isFinite(Number(c.source_in_frames))   || !Number.isFinite(Number(c.source_out_frames))) {
+      return res.status(400).json({ error: 'Clip frame fields must be finite numbers' });
+    }
+    if (!Number.isInteger(Number(c.track)) || Number(c.track) < 0) {
+      return res.status(400).json({ error: 'Clip track must be a non-negative integer' });
+    }
+  }
+
   const client = await pool.connect();
   try {
     await client.query('BEGIN');
@@ -160,7 +177,6 @@ router.put('/:id/clips', async (req, res, next) => {
       `DELETE FROM sequence_clips WHERE sequence_id = $1`,
       [req.params.id]
     );
-    const clips = Array.isArray(req.body) ? req.body : [];
     for (const c of clips) {
       await client.query(
         `INSERT INTO sequence_clips