fix: cache Convex JWT in server auth

tests/auth-server-jwt-cache.test.ts

@@ -0,0 +1,23 @@
+import assert from "node:assert/strict";
+import { readFile } from "node:fs/promises";
+import { join } from "node:path";
+import test from "node:test";
+
+const authServerPath = join(process.cwd(), "lib", "auth-server.ts");
+
+test("server auth utilities reuse valid Convex JWT cookies", async () => {
+  const source = await readFile(authServerPath, "utf8");
+
+  assert.match(source, /jwtCache:\s*\{/);
+  assert.match(source, /enabled:\s*true/);
+  assert.match(source, /isAuthError:\s*isConvexAuthError/);
+});
+
+test("server auth error predicate keeps stale token refresh possible", async () => {
+  const source = await readFile(authServerPath, "utf8");
+
+  assert.match(source, /function isConvexAuthError\(error: unknown\): boolean/);
+  assert.match(source, /Unauthenticated/);
+  assert.match(source, /Unauthorized/);
+  assert.doesNotMatch(source, /InvalidToken/);
+});