fix(server): Unix 默认组合在 rloop 不可用时退回 uvicorn+uvloop

- pick_server(auto) 按平台组合选择：Windows granian+winloop；Unix granian+rloop → uvicorn+uvloop → 已安装项
- 回退 uvicorn 时打印原因（未安装 granian / rloop 不可用）
- 测试补充 Unix 回退分支与 Windows auto 选择；README 默认矩阵同步

README.md

@@ -58,17 +58,17 @@ Node/TypeScript 版（v1.x，`master` 分支）：`pnpm install && pnpm start`
 | 平台 | 默认服务器 | 默认事件循环 |
 | --- | --- | --- |
 | Windows | granian | winloop（未安装则 asyncio） |
-| Linux / macOS | granian | rloop（未安装则 uvloop → asyncio） |
+| Linux / macOS | granian；rloop 不可用时退回 uvicorn | rloop；退回 uvicorn 时 uvloop（再退 asyncio） |
 | Windows + `--server uvicorn` | uvicorn | asyncio（uvicorn 不支持 winloop） |
 | Linux / macOS + `--server uvicorn` | uvicorn | uvloop（未安装则 asyncio） |
 
 事件循环可用 `auto / asyncio / rloop / uvloop / winloop`，参数与环境变量等价
-（`SERVER` / `LOOP` / `HOST` / `PORT` / `WORKERS` / `RELOAD`）。`auto` 会在启动器内解析成上表中的具体循环，
-启动日志会打印实际使用的组合；显式请求当前平台不可用的循环会直接报错并列出可用项（不会静默降级）。
+（`SERVER` / `LOOP` / `HOST` / `PORT` / `WORKERS` / `RELOAD`）。`auto` 会在启动器内解析成上表中的具体组合，
+启动日志会打印实际使用的 server+loop；显式请求当前平台不可用的循环会直接报错并列出可用项（不会静默降级）。
 
 ```bash
 uv sync                                                 # 默认依赖已含 granian[rloop/uvloop/winloop/reload]
-uv run python scripts/serve.py                          # Windows → granian+winloop；Unix → granian+rloop
+uv run python scripts/serve.py                          # Windows → granian+winloop；Unix → granian+rloop（缺 rloop 退 uvicorn+uvloop）
 uv run python scripts/serve.py --server uvicorn         # Unix → uvicorn+uvloop；Windows → uvicorn+asyncio
 uv run python scripts/serve.py --loop rloop             # 仅 Unix（Rust 事件循环）
 uv run python scripts/serve.py --loop uvloop            # 仅 Unix

scripts/serve.py

@@ -14,9 +14,10 @@
     uvloop    uvloop 包，仅 Unix
     winloop   winloop 包，仅 Windows（uvloop 的 Windows 实现）
 
-`auto` 在启动器内解析为具体循环，不交给服务器：
-    granian: Windows → winloop → asyncio；Unix → rloop → uvloop → asyncio
-    uvicorn: Windows → asyncio；Unix → uvloop → asyncio
+`auto` 在启动器内解析成具体组合，不交给服务器：
+    服务器：Windows → granian；Unix → granian+rloop，rloop 不可用时退回 uvicorn+uvloop
+    循环：  granian → Windows winloop / Unix rloop→uvloop→asyncio；
+            uvicorn → Unix uvloop→asyncio / Windows asyncio
 
 环境变量（参数优先）：SERVER / LOOP / HOST / PORT / WORKERS / RELOAD。
 PORT 默认读取 .env 后的 16688；HOST 默认 0.0.0.0（局域网播放器可直连）。
@@ -55,11 +56,21 @@ def has_module(name: str) -> bool:
 
 
 def pick_server(requested: str) -> str:
-    """auto：默认 granian（uv sync 已包含）；未安装时回退 uvicorn。"""
+    """auto：平台默认组合。
+
+    Windows：granian（+winloop）；Unix：granian+rloop，rloop 不可用时退回 uvicorn+uvloop，
+    最后才回退到已安装的服务器（循环由 default_loop 再降级）。
+    """
     if requested not in SERVERS:
         raise SystemExit(f"不支持的 server: {requested}（可选：{', '.join(SERVERS)}）")
     if requested != "auto":
         return requested
+    if IS_WINDOWS:
+        return "granian" if has_module("granian") else "uvicorn"
+    if has_module("granian") and has_module("rloop"):
+        return "granian"
+    if has_module("uvicorn") and has_module("uvloop"):
+        return "uvicorn"
     return "granian" if has_module("granian") else "uvicorn"
 
 
@@ -165,8 +176,9 @@ def main(argv: list[str] | None = None) -> int:
     server = pick_server(requested_server)
     if not has_module(server):
         raise SystemExit(f"未安装 {server}：uv sync（或 uv add {server}）")
-    if requested_server == "auto" and server == "uvicorn" and not has_module("granian"):
-        print("[serve] 未安装 granian，回退 uvicorn；uv sync 可安装默认的 granian 依赖", flush=True)
+    if requested_server == "auto" and server == "uvicorn":
+        reason = "未安装 granian" if not has_module("granian") else "rloop 不可用"
+        print(f"[serve] 默认组合回退 uvicorn（{reason}）；uv sync 会安装 granian+rloop 默认栈", flush=True)
 
     loop = resolve_loop(server, str(_arg_or_env(args.loop, "LOOP", "auto")))
     host = str(_arg_or_env(args.host, "HOST", "0.0.0.0"))

tests/test_serve.py

@@ -12,14 +12,28 @@ sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
 from scripts import serve
 
 
-def test_pick_server_auto_prefers_granian(monkeypatch: pytest.MonkeyPatch) -> None:
-    monkeypatch.setattr(serve, "has_module", lambda name: name == "granian")
+def test_pick_server_auto_windows_prefers_granian(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(serve, "IS_WINDOWS", True)
+    monkeypatch.setattr(serve, "has_module", lambda name: name in ("granian", "winloop"))
     assert serve.pick_server("auto") == "granian"
 
     monkeypatch.setattr(serve, "has_module", lambda name: False)
     assert serve.pick_server("auto") == "uvicorn"
 
 
+def test_pick_server_auto_unix_prefers_granian_rloop(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(serve, "IS_WINDOWS", False)
+    monkeypatch.setattr(serve, "has_module", lambda name: name in ("granian", "rloop", "uvloop", "uvicorn"))
+    assert serve.pick_server("auto") == "granian"
+
+
+def test_pick_server_auto_unix_falls_back_to_uvicorn_uvloop(monkeypatch: pytest.MonkeyPatch) -> None:
+    # 例如 granian 已安装但 rloop 不可用：默认改为 uvicorn+uvloop
+    monkeypatch.setattr(serve, "IS_WINDOWS", False)
+    monkeypatch.setattr(serve, "has_module", lambda name: name in ("granian", "uvloop", "uvicorn"))
+    assert serve.pick_server("auto") == "uvicorn"
+
+
 def test_available_loops_follow_installed_packages(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setattr(serve, "has_module", lambda name: name == "winloop")
     assert serve.available_loops("granian") == ["auto", "asyncio", "winloop"]