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

src/background-status-tool.test.ts

@@ -0,0 +1,27 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { createBackgroundRegistry } from "./background-registry.ts";
+import { createBackgroundStatusTool } from "./background-status-tool.ts";
+
+test("status tool shows active runs by default and can query single run", async () => {
+  const reg = createBackgroundRegistry();
+  reg.recordLaunch({ runId: "r1", preset: "p1", task: "t1" });
+  reg.recordLaunch({ runId: "r2", preset: "p2", task: "t2" });
+  reg.recordUpdate("r2", { status: "completed", exitCode: 0, finalText: "done" });
+
+  const tool = createBackgroundStatusTool({ registry: reg });
+  const resDefault: any = await tool.execute("id", {}, undefined, undefined, undefined);
+  // default should show only active (running) runs
+  assert.equal(resDefault.details.runs.length, 1);
+  assert.equal(resDefault.details.runs[0].runId, "r1");
+  assert.match(resDefault.content[0].text, /Active runs: 1/);
+
+  const resSingle: any = await tool.execute("id", { runId: "r2" }, undefined, undefined, undefined);
+  assert.equal(resSingle.details.runs.length, 1);
+  assert.equal(resSingle.details.runs[0].runId, "r2");
+  assert.match(resSingle.content[0].text, /status=completed/);
+
+  const resNotFound: any = await tool.execute("id", { runId: "nope" }, undefined, undefined, undefined);
+  assert.equal(resNotFound.details.runs.length, 0);
+  assert.match(resNotFound.content[0].text, /No run found/);
+});