feat(background): add background registry and status tool with tests

src/background-registry.test.ts

@@ -0,0 +1,42 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { createBackgroundRegistry } from "./background-registry.ts";
+
+test("recordLaunch and counts update correctly", () => {
+  const reg = createBackgroundRegistry();
+  reg.recordLaunch({ runId: "r1", preset: "p1", task: "t1" });
+  reg.recordLaunch({ runId: "r2", preset: "p2", task: "t2" });
+
+  let counts = reg.getCounts();
+  assert.equal(counts.running, 2);
+  assert.equal(counts.total, 2);
+
+  reg.recordUpdate("r2", { status: "completed", exitCode: 0, finalText: "done" });
+  counts = reg.getCounts();
+  assert.equal(counts.running, 1);
+  assert.equal(counts.completed, 1);
+  assert.equal(counts.total, 2);
+
+  const r1 = reg.getRun("r1");
+  const r2 = reg.getRun("r2");
+  assert.ok(r1);
+  assert.ok(r2);
+  assert.equal(r2?.finalText, "done");
+});
+
+test("replay seeds registry and counts", () => {
+  const reg = createBackgroundRegistry();
+  const now = Date.now();
+  reg.replay([
+    { runId: "a", preset: "p", task: "x", status: "running", startTime: now },
+    { runId: "b", preset: "p2", task: "y", status: "failed", startTime: now - 1000, endTime: now - 500 },
+  ]);
+
+  const counts = reg.getCounts();
+  assert.equal(counts.running, 1);
+  assert.equal(counts.failed, 1);
+  assert.equal(counts.total, 2);
+
+  const snap = reg.getSnapshot({ includeCompleted: true });
+  assert.equal(snap.length, 2);
+});