feat: add AI catalog description generation

frontend/src/api/client.test.ts

@@ -143,6 +143,27 @@ test("keeps only a known safe bounded JSON error payload", async () => {
   }
 });
 
+test.each([
+  ["description_generation_target_ids_duplicate", "Description generation target IDs must be unique."],
+  ["description_generation_no_eligible_targets", "No eligible catalog tables or columns need description generation."],
+  ["catalog_table_not_found", "One or more selected catalog tables were not found."],
+])("maps the description-generation error code %s to safe local copy", async (code, message) => {
+  const fetchSpy = vi.spyOn(globalThis, "fetch").mockResolvedValue(
+    new Response(JSON.stringify({ code, message: "provider detail must not be trusted" }), {
+      status: 400,
+      headers: { "content-type": "application/json" },
+    }),
+  );
+
+  try {
+    const failure = await apiFetch<unknown>("/description-generation-error")
+      .catch((error: unknown) => error) as ApiError;
+    expect(failure).toMatchObject({ code, message, payload: { code } });
+  } finally {
+    fetchSpy.mockRestore();
+  }
+});
+
 test("derives local messages without retaining a malicious known-code message", async () => {
   const fetchSpy = vi.spyOn(globalThis, "fetch").mockResolvedValue(
     new Response(JSON.stringify({