diff --git a/server/index.mjs b/server/index.mjs
index 9dd0b40..ba422d0 100644
--- a/server/index.mjs
+++ b/server/index.mjs
@@ -108,7 +108,7 @@ import {
   fetchGoogleLiked, fetchTwitchProfile, fetchTwitchFollows, hasGoogleWriteScope,
   fetchGoogleWatchLater, pushGoogleWatchLater, fetchInnerTubeHistory,
   fetchInnerTubeWatchLaterViaLib, pushInnerTubeWatchLater, fetchGoogleWatchLaterId,
-  fetchAccountChannels,
+  fetchAccountChannels, diagnoseInnertube,
 } from './oauth.mjs';
 import { getSearchMode, getYtDlpBin, hasCookiesFile, metricsSnapshot } from './providers/youtube-common.mjs';
 import { ytScrapeCacheStats } from './providers/youtube.mjs';
@@ -585,6 +585,28 @@ r.get('/oauth/google/yt-channels', authMiddlewareCookieAware, oauthLimiter, asyn
   }
 });
 
+// Diagnostic : état de chaque endpoint InnerTube authentifié + Data API.
+r.get('/oauth/google/diag', authMiddlewareCookieAware, oauthLimiter, async (req, res) => {
+  try {
+    const conn = await freshOAuthToken(req.user.id, 'google');
+    const dataApi = {};
+    try {
+      await fetchGoogleWatchLaterId(conn.accessToken);
+      dataApi.watchLaterId = true;
+    } catch (e) {
+      dataApi.watchLaterId = false;
+      dataApi.watchLaterError = String(e?.message || '').slice(0, 80);
+    }
+    const innertube = await diagnoseInnertube(conn);
+    try {
+      console.log(`[oauth] diag user=${req.user?.id} ${JSON.stringify({ dataApi, innertube }).slice(0, 800)}`);
+    } catch {}
+    return res.json({ dataApi, innertube });
+  } catch (error) {
+    return res.status(error?.status || 502).json({ error: error?.message || 'diag_failed' });
+  }
+});
+
 r.put('/oauth/google/yt-channel', authMiddlewareCookieAware, oauthLimiter, (req, res) => {
   try {
     const channelId = String(req.body?.channelId || '').trim().slice(0, 64) || null;
diff --git a/server/oauth.mjs b/server/oauth.mjs
index 388e461..533e589 100644
--- a/server/oauth.mjs
+++ b/server/oauth.mjs
@@ -717,6 +717,50 @@ function textOf(t) {
   return String(t?.simpleText || '');
 }
 
+/**
+ * Diagnostic InnerTube authentifié : teste plusieurs endpoints et rapporte
+ * pour chacun ok/count ou le motif YouTube. But : isoler un rejet global
+ * du compte d'un problème spécifique à l'historique.
+ */
+export async function diagnoseInnertube(conn) {
+  const out = {};
+  let innertube = null;
+  try {
+    innertube = await getAuthedInnertube(conn);
+    out.session = { ok: true };
+  } catch (e) {
+    out.session = { ok: false, reason: String(e?.message || e).slice(0, 200) };
+    return out;
+  }
+  const probe = async (name, fn) => {
+    try {
+      const r = await fn();
+      out[name] = { ok: true, ...r };
+    } catch (e) {
+      out[name] = { ok: false, reason: libErrorDetail(e) };
+    }
+  };
+  await probe('subscriptionsFeed', async () => {
+    const feed = await innertube.getSubscriptionsFeed();
+    return { count: Array.isArray(feed?.contents) ? feed.contents.length : 0 };
+  });
+  await probe('library', async () => {
+    await innertube.getLibrary();
+    return {};
+  });
+  await probe('accountMenu', async () => {
+    const data = await innertube.session.actions.execute('/account/account_menu', {});
+    const blob = JSON.stringify(data?.data || data || '').slice(0, 200);
+    return { sample: blob.slice(0, 120) };
+  });
+  await probe('history', async () => {
+    const feed = await innertube.getHistory();
+    const n = Array.isArray(feed?.sections) ? feed.sections.reduce((a, s) => a + (s?.contents?.length || 0), 0) : 0;
+    return { count: n };
+  });
+  return out;
+}
+
 /**
  * Chaînes YouTube du compte (sélecteur façon SmartTube) via account_menu.
  * La chaîne par défaut peut être une coquille vide (relatedPlaylists sans
diff --git a/src/components/library/import/import.component.html b/src/components/library/import/import.component.html
index 7e22c5b..357410a 100644
--- a/src/components/library/import/import.component.html
+++ b/src/components/library/import/import.component.html
@@ -101,7 +101,12 @@
         class="rounded-md border border-slate-700 bg-slate-800 px-3 py-1.5 text-sm text-slate-200 transition hover:border-slate-500">
         {{ ytChannelsLoading() ? 'Chargement…' : (ytChannels().length ? 'Recharger' : 'Lister mes chaînes') }}
       </button>
+      <button type="button" (click)="loadDiag()" [disabled]="diagLoading()"
+        class="rounded-md border border-slate-700 bg-slate-800 px-3 py-1.5 text-sm text-slate-200 transition hover:border-slate-500">
+        {{ diagLoading() ? 'Diagnostic…' : '🩺 Diagnostic complet' }}
+      </button>
     </div>
+    <pre *ngIf="diagResult()" class="mt-2 max-h-64 overflow-auto whitespace-pre-wrap rounded-lg border border-slate-700 bg-slate-950 p-2 text-xs text-slate-300">{{ diagResult() }}</pre>
     <div *ngIf="ytChannelsError()" class="mt-2 rounded-lg border border-red-700 bg-red-900/30 p-2 text-xs text-red-200">{{ ytChannelsError() }}</div>
     <div *ngIf="ytChannels().length" class="mt-3 space-y-2">
       <label *ngFor="let c of ytChannels()" class="flex cursor-pointer items-center gap-3 rounded-lg border border-slate-700 bg-slate-800/60 px-3 py-2 text-sm transition hover:border-slate-500">
diff --git a/src/components/library/import/import.component.ts b/src/components/library/import/import.component.ts
index d966c3e..d619dbb 100644
--- a/src/components/library/import/import.component.ts
+++ b/src/components/library/import/import.component.ts
@@ -249,6 +249,24 @@ export class ImportComponent implements OnInit {
   ytSelectedChannelId = signal<string>('');
   ytSavingChannel = signal(false);
   ytChannelSaved = signal<string | null>(null);
+  diagLoading = signal(false);
+  diagResult = signal<string | null>(null);
+
+  loadDiag(): void {
+    if (this.diagLoading()) return;
+    this.diagLoading.set(true);
+    this.diagResult.set(null);
+    this.api.diag().subscribe({
+      next: (res) => {
+        this.diagResult.set(JSON.stringify(res, null, 1));
+        this.diagLoading.set(false);
+      },
+      error: (e) => {
+        this.diagResult.set(`Erreur diag : ${e?.error?.error || e?.message || 'diag_failed'}`);
+        this.diagLoading.set(false);
+      },
+    });
+  }
 
   loadYtChannels(): void {
     if (!this.isConnected('google') || this.ytChannelsLoading()) return;
diff --git a/src/services/oauth-import.service.ts b/src/services/oauth-import.service.ts
index 4350d61..f6a426d 100644
--- a/src/services/oauth-import.service.ts
+++ b/src/services/oauth-import.service.ts
@@ -101,6 +101,11 @@ export class OAuthImportService {
   saveYtChannel(channelId: string | null, pageId: string | null): Observable<{ selected: { channelId: string | null; pageId: string | null } }> {
     return this.http.put<any>(`/api/oauth/google/yt-channel`, { channelId, pageId });
   }
+
+  /** Diagnostic : état de chaque endpoint authentifié (Data API + InnerTube). */
+  diag(): Observable<any> {
+    return this.http.get<any>(`/api/oauth/google/diag`);
+  }
 }
 
 /** Parse local du `watch-history.json` de Google Takeout (confidentiel : rien n'est uploadé tel quel). */