chore: import upstream snapshot with attribution

tests/unit/models-test-error-shape.test.ts

@@ -0,0 +1,65 @@
+// Regression guard: POST /api/models/test must always return a STRING `error`,
+// never an object. The Zod-validation and invalid-JSON paths used to return
+// `{ error: <object> }` (Zod .format() / a details object). The dashboard renders
+// that value directly in a toast, so an object froze the whole page (React #31).
+// The "test a model → screen froze" bug.
+//
+// DB handles released in test.after (CLAUDE.md learning: unreleased SQLite
+// handles hang node:test).
+
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-models-test-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+
+const core = await import("../../src/lib/db/core.ts");
+const settingsDb = await import("../../src/lib/db/settings.ts");
+const route = await import("../../src/app/api/models/test/route.ts");
+
+test.before(async () => {
+  await settingsDb.updateSettings({ requireLogin: false });
+});
+
+test.after(async () => {
+  core.resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+function post(body: unknown, rawText?: string) {
+  return route.POST(
+    new Request("http://localhost:20128/api/models/test", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: rawText !== undefined ? rawText : JSON.stringify(body),
+    })
+  );
+}
+
+test("Zod validation failure returns a STRING error (not an object)", async () => {
+  // connectionId "" fails z.string().min(1).optional() -> validation error path
+  const res = await post({ providerId: "openai", modelId: "gpt-4o", connectionId: "" });
+  assert.equal(res.status, 400);
+  const body = await res.json();
+  assert.equal(typeof body.error, "string", "error must be a string, never an object");
+  assert.equal(body.status, "error");
+  assert.match(body.error, /Invalid request/i);
+});
+
+test("missing required field returns a STRING error", async () => {
+  const res = await post({ providerId: "openai" }); // no modelId
+  assert.equal(res.status, 400);
+  const body = await res.json();
+  assert.equal(typeof body.error, "string");
+});
+
+test("invalid JSON body returns a STRING error (not an object)", async () => {
+  const res = await post(undefined, "{ not json ");
+  assert.equal(res.status, 400);
+  const body = await res.json();
+  assert.equal(typeof body.error, "string");
+  assert.match(body.error, /Invalid JSON/i);
+});