fix(pet): a member's pet chat starts in <their folder>/sagi

POST /api/lanes/ensure without a cwd defaulted to the dashboard's own
home, outside a member's folder, so every member's pet chat failed with
"a workspace must be inside your own folder" (EFOLDER). A member now
gets <their folder>/sagi, made as them (write-as mkdir) on first use.

server/__tests__/server-s3-lanes.test.js

@@ -192,3 +192,31 @@ describe("a member's new project folder", () => {
     assert.equal(fs.existsSync(path.join(TMP, "host-new")), false);
   });
 });
+
+describe("the pet chat's workspace for a member", () => {
+  it("is <their folder>/sagi, made as them — never the host's home (EFOLDER)", async () => {
+    const { fakeSudo } = require("./fixtures/fake-sudo");
+    const sudo = fakeSudo();
+    runAs.__setExecImpl(sudo.exec);
+    const login = await fetch(`${BASE}/api/auth/login`, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ username: "mia", password: "member-pass-1" }),
+    });
+    const cm = login.headers.get("set-cookie").split(";")[0];
+    const ensure = () =>
+      fetch(`${BASE}/api/lanes/ensure`, {
+        method: "POST",
+        headers: { "Content-Type": "application/json", cookie: cm },
+        body: JSON.stringify({ title: "Sagi" }),
+      }).then(async (r) => ({ status: r.status, body: await r.json() }));
+    const first = await ensure();
+    assert.equal(first.status, 201, JSON.stringify(first.body));
+    const want = fs.realpathSync(path.join(USERS, "mia", "sagi"));
+    assert.equal(first.body.lane.cwd, want);
+    const mk = sudo.calls.find((c) => c.includes("/opt/agenthub/libexec/write-as"));
+    assert.ok(mk && mk.includes("ah-mia") && mk.includes("mkdir"));
+    const again = await ensure();
+    assert.equal(again.body.lane.id, first.body.lane.id, "the same workspace next time");
+  });
+});