diff --git a/Dockerfile b/Dockerfile
index 0647e74..37e9af4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -34,5 +34,9 @@ USER app
 
 EXPOSE 3000
 ENV PORT=3000 HOSTNAME=0.0.0.0
+# Must match the volume mount in docker-compose.yml. Without this, uploads
+# default to `$cwd/data/uploads` (i.e. /app/data/uploads here) — not the
+# persisted volume — so files vanish on every container restart/redeploy.
+ENV UPLOAD_DIR=/data/uploads
 
 ENTRYPOINT ["sh", "./docker-entrypoint.sh"]
diff --git a/src/app/api/materials/[id]/file/route.ts b/src/app/api/materials/[id]/file/route.ts
index 81b1bff..bc519a6 100644
--- a/src/app/api/materials/[id]/file/route.ts
+++ b/src/app/api/materials/[id]/file/route.ts
@@ -19,7 +19,16 @@ export async function GET(
     return new Response("Not found", { status: 404 })
   }
 
-  const size = row.sizeBytes ?? (await fileSize(row.storagePath))
+  // Confirm the file actually exists on disk before streaming: if it's
+  // missing (e.g. storage misconfiguration), fail fast with a clean 404
+  // instead of erroring mid-stream, which surfaces to clients as a broken
+  // connection / 502 through the reverse proxy.
+  let size: number
+  try {
+    size = await fileSize(row.storagePath)
+  } catch {
+    return new Response("Not found", { status: 404 })
+  }
   // Re-sanitize at serve time so rows created before the upload-side
   // sanitization can't serve active content either.
   const mime = safeInlineMime(row.mimeType)