feat(acp): add experimental ACP support

Co-authored-by: Jonathan Taylor <visionik@pobox.com>

src/acp/session.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it, afterEach } from "vitest";
+
+import { createInMemorySessionStore } from "./session.js";
+
+describe("acp session manager", () => {
+  const store = createInMemorySessionStore();
+
+  afterEach(() => {
+    store.clearAllSessionsForTest();
+  });
+
+  it("tracks active runs and clears on cancel", () => {
+    const session = store.createSession({
+      sessionKey: "acp:test",
+      cwd: "/tmp",
+    });
+    const controller = new AbortController();
+    store.setActiveRun(session.sessionId, "run-1", controller);
+
+    expect(store.getSessionByRunId("run-1")?.sessionId).toBe(session.sessionId);
+
+    const cancelled = store.cancelActiveRun(session.sessionId);
+    expect(cancelled).toBe(true);
+    expect(store.getSessionByRunId("run-1")).toBeUndefined();
+  });
+});