feat(logging): add structured server diagnostics

packages/logging/test/logger.test.ts

@@ -0,0 +1,31 @@
+import { Writable } from "node:stream";
+import { describe, expect, it } from "vitest";
+import { createLogger } from "../src/index";
+
+function captureLog() {
+  let output = "";
+  const destination = new Writable({
+    write(chunk, _encoding, callback) {
+      output += chunk.toString();
+      callback();
+    },
+  });
+  return { destination, read: () => JSON.parse(output.trim()) as Record<string, unknown> };
+}
+
+describe("structured application logging", () => {
+  it("emits service metadata and redacts credential fields", () => {
+    const capture = captureLog();
+    const logger = createLogger("account-manager-test", { destination: capture.destination });
+
+    logger.info({ token: "secret-token", apiKey: "secret-key", operation: "test" }, "Test event");
+
+    expect(capture.read()).toMatchObject({
+      service: "account-manager-test",
+      token: "[Redacted]",
+      apiKey: "[Redacted]",
+      operation: "test",
+      msg: "Test event",
+    });
+  });
+});