diff --git a/artifacts/api-server/src/routes/notes.ts b/artifacts/api-server/src/routes/notes.ts
index bca3ae8c..29ffe2d1 100644
--- a/artifacts/api-server/src/routes/notes.ts
+++ b/artifacts/api-server/src/routes/notes.ts
@@ -31,6 +31,15 @@ function parseIdParam(raw: unknown): { ok: true; id: number } | { ok: false; err
   return { ok: true, id: n };
 }
 
+// Postgres unique-constraint violation (SQLSTATE 23505). Used to distinguish
+// duplicate-name errors (→ 409) from unrelated DB failures (→ 500).
+function isUniqueViolation(e: unknown): boolean {
+  return (
+    typeof e === "object" && e !== null && "code" in e &&
+    (e as { code?: unknown }).code === "23505"
+  );
+}
+
 function parseStringMax(v: unknown, max: number): string | undefined {
   if (v === undefined || v === null) return undefined;
   if (typeof v !== "string") return undefined;
@@ -942,7 +951,11 @@ router.post("/note-folders", requireAuth, async (req, res): Promise<void> => {
       .returning();
     res.status(201).json({ ...folder, noteCount: 0 });
   } catch (e) {
-    res.status(409).json({ error: "Folder already exists" });
+    if (isUniqueViolation(e)) {
+      res.status(409).json({ error: "Folder already exists" });
+      return;
+    }
+    throw e;
   }
 });
 
@@ -983,7 +996,11 @@ router.patch("/note-folders/:id", requireAuth, async (req, res): Promise<void> =
       );
     res.json({ ...folder, noteCount: Number(countRow?.count ?? 0) });
   } catch (e) {
-    res.status(409).json({ error: "Folder already exists" });
+    if (isUniqueViolation(e)) {
+      res.status(409).json({ error: "Folder already exists" });
+      return;
+    }
+    throw e;
   }
 });