Preview a match by join code before joining

GET /api/games/preview returns the lobby behind a code plus the game's
name and engine-echoed options. The lobby debounces the lookup as a
complete code is typed and shows the game, seated players, open seats
and option badges rendered from the game's schema, disabling Join when
the lobby is full or the match has already started.

server/tests/test_routes_games.py

@@ -116,6 +116,55 @@ class GamesRouteTest(unittest.TestCase):
                 )
             self.assertEqual(400, invalid.status_code)
 
+    @async_test
+    async def test_preview_join_code(self) -> None:
+        transport = ASGITransport(app=app)
+        async with AsyncClient(transport=transport, base_url="http://127.0.0.1") as client:
+            with oidc_user("alice"):
+                created = await client.post(
+                    "/api/games",
+                    json={
+                        "options": {
+                            "target_score": 16,
+                            "napola": False,
+                            "asso_pigliatutto": True,
+                        }
+                    },
+                )
+            code = created.json()["join_code"]
+
+            response = await client.get(f"/api/games/preview?code={code}")
+            self.assertEqual(401, response.status_code)
+
+            with oidc_user("bob"):
+                missing = await client.get("/api/games/preview")
+                unknown = await client.get("/api/games/preview?code=ZZZZZZ")
+            self.assertEqual(400, missing.status_code)
+            self.assertEqual(404, unknown.status_code)
+
+            with oidc_user("bob"):
+                preview = await client.get(f"/api/games/preview?code={code}")
+            self.assertEqual(200, preview.status_code)
+            body = preview.json()
+            self.assertEqual("scopone_scientifico", body["game_type"])
+            self.assertEqual("Scopone scientifico", body["game_name"])
+            self.assertTrue(body["game_description"])
+            self.assertEqual("lobby", body["phase"])
+            self.assertEqual(16, body["target_score"])
+            self.assertFalse(body["napola"])
+            self.assertTrue(body["asso_pigliatutto"])
+            self.assertEqual(3, body["seats_open"])
+            self.assertEqual(["alice"], [p["sub"] for p in body["players"]])
+
+            for player in ("bob", "carol", "dave"):
+                with oidc_user(player):
+                    await client.post("/api/games/join", json={"code": code})
+            with oidc_user("bob"):
+                started = await client.get(f"/api/games/preview?code={code}")
+            self.assertEqual(200, started.status_code)
+            self.assertEqual("playing", started.json()["phase"])
+            self.assertEqual(0, started.json()["seats_open"])
+
     @async_test
     async def test_join_errors(self) -> None:
         transport = ASGITransport(app=app)