diff --git a/server/__tests__/youtube-api-url.test.js b/server/__tests__/youtube-api-url.test.js
index b6ce095..3321348 100644
--- a/server/__tests__/youtube-api-url.test.js
+++ b/server/__tests__/youtube-api-url.test.js
@@ -199,3 +199,44 @@ test('scrapeYouTube: a hostile @handle cannot truncate or inject parameters', as
     else process.env.YOUTUBE_API_KEY = oldKey;
   }
 });
+
+// ---------------------------------------------------------------------------
+// Coverage guard.
+//
+// The builder only helps where it is used, and the original injection survived
+// precisely because it was spread across ~13 hand-rolled call sites. This walks
+// server/ and fails if any module builds a Data API URL directly again.
+// ---------------------------------------------------------------------------
+
+const fs = require('node:fs');
+const path = require('node:path');
+
+test('no module builds a YouTube Data API URL by hand', () => {
+  const root = path.join(__dirname, '..');
+  const skipDirs = new Set(['node_modules', '__tests__']);
+  // youtube-api.js owns the one literal. publish/oauth.js holds a static OAuth
+  // userinfo URL with no interpolated values (mine=true), so nothing
+  // user-supplied can reach it.
+  const allowed = new Set(['youtube-api.js', path.join('publish', 'oauth.js')]);
+
+  const offenders = [];
+  (function walk(dir) {
+    for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+      const full = path.join(dir, entry.name);
+      if (entry.isDirectory()) {
+        if (!skipDirs.has(entry.name)) walk(full);
+        continue;
+      }
+      if (!entry.name.endsWith('.js')) continue;
+      const rel = path.relative(root, full);
+      if (allowed.has(rel)) continue;
+      if (fs.readFileSync(full, 'utf8').includes('googleapis.com/youtube/v3')) offenders.push(rel);
+    }
+  })(root);
+
+  assert.deepStrictEqual(
+    offenders, [],
+    'these build a YouTube Data API URL directly — route them through ' +
+    'youtubeApiUrl() instead:\n  ' + offenders.join('\n  ')
+  );
+});
diff --git a/server/content-metrics.js b/server/content-metrics.js
index 0dc1884..162a641 100644
--- a/server/content-metrics.js
+++ b/server/content-metrics.js
@@ -8,6 +8,7 @@
 const fetch = require('./proxy-fetch');
 const { safeFetchRaw } = require('./web/web-fetch');
 const log = require('./logger');
+const { youtubeApiUrl } = require('./youtube-api');
 const YOUTUBE_API_KEY = process.env.YOUTUBE_API_KEY;
 
 // `content_url` is user-supplied, so `hostname.includes('tiktok.com')` was
@@ -68,7 +69,9 @@ async function scrapeYouTubeVideo(url) {
 
   try {
     const res = await fetch(
-      `https://www.googleapis.com/youtube/v3/videos?part=statistics,snippet&id=${encodeURIComponent(videoId)}&key=${YOUTUBE_API_KEY}`
+      youtubeApiUrl('videos', {
+        part: ['statistics', 'snippet'], id: videoId, key: YOUTUBE_API_KEY,
+      })
     );
     const data = await res.json();
     const video = data.items?.[0];
diff --git a/server/youtube-discovery.js b/server/youtube-discovery.js
index 56ee5d0..7b2cd05 100644
--- a/server/youtube-discovery.js
+++ b/server/youtube-discovery.js
@@ -5,6 +5,7 @@
 
 const fetch = require('./proxy-fetch');
 const quota = require('./youtube-quota');
+const { youtubeApiUrl } = require('./youtube-api');
 const YOUTUBE_API_KEY = process.env.YOUTUBE_API_KEY;
 
 function detectCategory(text) {
@@ -61,7 +62,10 @@ async function searchYouTubeChannels({ keywords, maxResults = 50, minSubscribers
       }
 
       const searchRes = await fetch(
-        `https://www.googleapis.com/youtube/v3/search?part=snippet&type=channel&q=${encodeURIComponent(query)}&maxResults=${Math.min(maxResults, 50)}&key=${YOUTUBE_API_KEY}`
+        youtubeApiUrl('search', {
+          part: 'snippet', type: 'channel', q: query,
+          maxResults: Math.min(maxResults, 50), key: YOUTUBE_API_KEY,
+        })
       );
       const searchData = await searchRes.json();
       quota.record('search', 1);
@@ -85,7 +89,9 @@ async function searchYouTubeChannels({ keywords, maxResults = 50, minSubscribers
       }
 
       const statsRes = await fetch(
-        `https://www.googleapis.com/youtube/v3/channels?part=snippet,statistics&id=${channelIds.map(encodeURIComponent).join(',')}&key=${YOUTUBE_API_KEY}`
+        youtubeApiUrl('channels', {
+          part: ['snippet', 'statistics'], id: channelIds, key: YOUTUBE_API_KEY,
+        })
       );
       const statsData = await statsRes.json();
       quota.record('channels', 1);