test: use-case coverage + end-to-end smoke test

- tests/test_coven.py: capacity cap (5th rejected, configurable), duplicate
  username, roster frame contents, slot/username freed on disconnect.
- tests/conftest.py: set app.ctx.max_users (fixes fixture vs new server code).
- hh/smoke.sh: one-command e2e — rust unit tests, SRP self-test, boot server,
  rust handshake round-trip, cross-language python decrypt of a rust message.
- hh: drop unused Session.user_id (clean build).

pytest: 85 passed. smoke: PASS.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/conftest.py

@@ -32,6 +32,7 @@ def app():
     app.ctx.admin_token = "test-admin-token"
     from cmd_chat.server.helpers import RateLimiter
     app.ctx.rate_limiter = RateLimiter(max_requests=100, window_seconds=60)
+    app.ctx.max_users = 4
     app.ctx.cleanup_task = None
 
     register_routes(app)

tests/test_coven.py

@@ -0,0 +1,90 @@
+"""Use-case tests for the hack-house multi-user coven features (capacity cap,
+roster, username + slot lifecycle). In-process via sanic-testing.
+"""
+import base64
+import json
+
+import srp
+
+from cmd_chat.server.models import UserSession
+from cmd_chat.server.views import _roster_frame
+
+
+def _add_member(app, name):
+    """Seat a verified member directly in the session store."""
+    app.ctx.session_store.add(
+        UserSession(user_id=f"id-{name}", ip="127.0.0.1", username=name)
+    )
+
+
+def _init(test_client, name):
+    """Run /srp/init for a fresh username (just the first handshake leg)."""
+    usr = srp.User(b"chat", b"testpassword")
+    _, A = usr.start_authentication()
+    return test_client.post(
+        "/srp/init",
+        json={"username": name, "A": base64.b64encode(A).decode()},
+    )
+
+
+class TestCovenCapacity:
+    def test_accepts_up_to_capacity(self, app, test_client):
+        app.ctx.max_users = 4
+        for n in ("a", "b", "c"):
+            _add_member(app, n)
+        # 4th seat is still available
+        _, resp = _init(test_client, "fourth")
+        assert resp.status == 200
+
+    def test_rejects_when_full(self, app, test_client):
+        app.ctx.max_users = 4
+        for n in ("a", "b", "c", "d"):
+            _add_member(app, n)
+        _, resp = _init(test_client, "fifth")
+        assert resp.status == 409
+        assert "full" in resp.json["error"].lower()
+
+    def test_capacity_is_configurable(self, app, test_client):
+        app.ctx.max_users = 2
+        for n in ("a", "b"):
+            _add_member(app, n)
+        _, resp = _init(test_client, "third")
+        assert resp.status == 409
+
+
+class TestUsernames:
+    def test_duplicate_username_rejected(self, app, test_client):
+        _add_member(app, "ghost")
+        _, resp = _init(test_client, "ghost")
+        assert resp.status == 409
+        assert "taken" in resp.json["error"].lower()
+
+
+class TestRoster:
+    def test_roster_frame_contents(self, app):
+        _add_member(app, "alice")
+        _add_member(app, "bob")
+        frame = json.loads(_roster_frame(app))
+        assert frame["type"] == "roster"
+        assert frame["capacity"] == app.ctx.max_users
+        assert {u["username"] for u in frame["users"]} == {"alice", "bob"}
+        assert all("user_id" in u for u in frame["users"])
+
+
+class TestSlotLifecycle:
+    def test_disconnect_frees_slot_and_username(self, app, test_client):
+        app.ctx.max_users = 1
+        _add_member(app, "ghost")
+        assert app.ctx.session_store.username_exists("ghost")
+        # full room rejects a newcomer
+        _, resp = _init(test_client, "intruder")
+        assert resp.status == 409
+
+        # the disconnect path removes the session (frees slot + name)
+        app.ctx.session_store.remove("id-ghost")
+        assert not app.ctx.session_store.username_exists("ghost")
+        assert app.ctx.session_store.count() == 0
+
+        # name is reusable and the slot is open again
+        _, resp = _init(test_client, "ghost")
+        assert resp.status == 200