diff --git a/backend/lib/squid.js b/backend/lib/squid.js
index 7c39231..2e94685 100644
--- a/backend/lib/squid.js
+++ b/backend/lib/squid.js
@@ -106,8 +106,8 @@ async function getAltchaCookie() {
   // 2. Solve PoW
   const solution = await solveAltcha(challenge);
 
-  // 3. Verify — payload contains the unwrapped challenge params + our solution
-  const payload = Buffer.from(JSON.stringify({ challenge, solution })).toString('base64');
+  // 3. Verify — include the top-level signature so the server can authenticate the challenge
+  const payload = Buffer.from(JSON.stringify({ challenge, solution, signature: chBody.signature })).toString('base64');
   const vRes = await httpsPost(`${SQUID_BASE}/api/altcha/verify`, { payload });
   if (vRes.status !== 200) throw new Error(`ALTCHA verify HTTP ${vRes.status}`);
 
diff --git a/backend/lib/ytdlp.js b/backend/lib/ytdlp.js
index fd3a0af..57eb964 100644
--- a/backend/lib/ytdlp.js
+++ b/backend/lib/ytdlp.js
@@ -28,18 +28,19 @@ function buildTitleKeywords(title) {
 
 function buildVariantFilter(title) {
   const t = (title || '').toLowerCase();
+  // !~= (?i) is yt-dlp's case-insensitive "does not match regex" — catches Remix/REMIX/remix etc.
   const RULES = [
-    { key: 'sped',         expr: 'title !*= sped' },
-    { key: 'speedup',      expr: 'title !*= speedup' },
-    { key: 'slowed',       expr: 'title !*= slowed' },
-    { key: 'reverb',       expr: 'title !*= reverb' },
-    { key: 'nightcore',    expr: 'title !*= nightcore' },
-    { key: 'karaoke',      expr: 'title !*= karaoke' },
-    { key: 'parody',       expr: 'title !*= parody' },
-    { key: 'remix',        expr: 'title !*= remix' },
-    { key: 'cover',        expr: 'title !*= cover' },
-    { key: 'acoustic',     expr: 'title !*= acoustic' },
-    { key: 'instrumental', expr: 'title !*= instrumental' },
+    { key: 'sped',         expr: 'title !~= (?i)sped up' },
+    { key: 'speedup',      expr: 'title !~= (?i)speed\\s*up' },
+    { key: 'slowed',       expr: 'title !~= (?i)slowed' },
+    { key: 'reverb',       expr: 'title !~= (?i)reverb' },
+    { key: 'nightcore',    expr: 'title !~= (?i)nightcore' },
+    { key: 'karaoke',      expr: 'title !~= (?i)karaoke' },
+    { key: 'parody',       expr: 'title !~= (?i)parody' },
+    { key: 'remix',        expr: 'title !~= (?i)remix' },
+    { key: 'cover',        expr: 'title !~= (?i)cover' },
+    { key: 'acoustic',     expr: 'title !~= (?i)acoustic' },
+    { key: 'instrumental', expr: 'title !~= (?i)instrumental' },
   ];
   const parts = RULES.filter(r => !t.includes(r.key)).map(r => r.expr);
   return parts.length ? parts.join(' & ') : '';