fix(backend): validate configured model provider pair

backend/test/routes-sql-meta.test.ts

@@ -1,4 +1,4 @@
-import { test, expect } from "vitest";
+import { test, expect, vi } from "vitest";
 import { buildApp } from "../src/app.js";
 import { loadConfig } from "../src/config.js";
 
@@ -148,6 +148,20 @@ test("GET /models returns {models:[]} when listModels throws (graceful fallback)
   expect(res.json()).toEqual({ models: [] });
 });
 
+test("GET /models logs a sanitized warning when listing fails", async () => {
+  const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
+    thtRunner: {} as any,
+    listModels: async () => { throw new Error("credential-value-must-not-appear"); },
+  });
+  const warn = vi.spyOn(app.log, "warn");
+
+  const res = await app.inject({ method: "GET", url: "/models" });
+
+  expect(res.json()).toEqual({ models: [] });
+  expect(JSON.stringify(warn.mock.calls)).not.toContain("credential-value-must-not-appear");
+  expect(warn).toHaveBeenCalled();
+});
+
 test("GET /models with empty listModels stub returns empty array", async () => {
   const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
     thtRunner: {} as any,