feat: 模型推理异步加载与对话链路修复，同步基线

模型推理全异步化改造：
- 计算节点 InferenceSession 改为后台线程异步加载模型，load 立即返回，
  加载期间事件循环保持响应（/inference/status 与 /health 不阻塞）
- 后端模型加载改为异步派发 + 轮询对账器（reconcile_inference_loads），
  任务状态由 starting 自动推进到 ready/error，解决多节点启动超时
  （timeout of 120000ms exceeded）
- 推理删除/卸载改为任务感知 + 短超时，删除先删记录再 best-effort 卸载，
  不再被不可达节点阻塞；同节点新模型替换旧任务标记失效
- 流式对话透传 task_id/node_id 路由到真正加载模型的算力节点，
  useStreamChat 解析 SSE 错误帧以干净文案展示
- 对话历史按任务 id 本地持久化，退出重进可恢复；移除页脚提示文本
- 新增后端推理异步加载与计算节点异步状态机单元测试

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

compute/tests/test_inference_session.py

@@ -0,0 +1,127 @@
+from __future__ import annotations
+
+import sys
+import time
+import types
+from typing import Any
+
+import pytest
+
+from compute.engines.llama_factory.inference import InferenceSession
+
+# 模拟模型加载耗时，用于验证 load() 立即返回、info() 不阻塞
+LOAD_DELAY = 0.2
+
+
+class FakeChatModel:
+    def __init__(self, args: dict[str, Any]) -> None:
+        time.sleep(LOAD_DELAY)
+        self.tokenizer = object()
+        self.engine = types.SimpleNamespace(tokenizer=object())
+        self._output = "hello from model"
+
+    def stream_chat(self, *args, **kwargs):
+        for _ in range(1):
+            yield self._output
+
+
+class FailingChatModel:
+    def __init__(self, args: dict[str, Any]) -> None:
+        time.sleep(LOAD_DELAY)
+        raise RuntimeError("boom: fake load failure")
+
+
+def _get_infer_args(args: dict[str, Any]) -> list[Any]:
+    # 最后一个元素为 generating_args，worker 会转成 dict
+    return [None, None, {"temperature": 0.7}]
+
+
+def _install_llamafactory(monkeypatch, chat_model: type) -> None:
+    llmf = types.ModuleType("llamafactory")
+    chat_mod = types.ModuleType("llamafactory.chat")
+    hparams_mod = types.ModuleType("llamafactory.hparams")
+    chat_mod.ChatModel = chat_model
+    hparams_mod.get_infer_args = _get_infer_args
+    llmf.chat = chat_mod
+    llmf.hparams = hparams_mod
+    monkeypatch.setitem(sys.modules, "llamafactory", llmf)
+    monkeypatch.setitem(sys.modules, "llamafactory.chat", chat_mod)
+    monkeypatch.setitem(sys.modules, "llamafactory.hparams", hparams_mod)
+
+
+@pytest.fixture
+def stub_llamafactory(monkeypatch) -> None:
+    _install_llamafactory(monkeypatch, FakeChatModel)
+
+
+@pytest.fixture
+def stub_failing_llamafactory(monkeypatch) -> None:
+    _install_llamafactory(monkeypatch, FailingChatModel)
+
+
+def _wait_for_status(session: InferenceSession, status: str, timeout: float = 3.0) -> bool:
+    deadline = time.time() + timeout
+    while time.time() < deadline:
+        if session.info()["status"] == status:
+            return True
+        time.sleep(0.02)
+    return False
+
+
+def test_load_returns_immediately_then_ready(stub_llamafactory) -> None:
+    session = InferenceSession()
+    started = time.time()
+    result = session.load("/models/qwen")
+    assert result["status"] == "loading"
+    assert result["loaded"] is False
+    assert result["request_id"]
+    # 在慢加载完成前就返回，且 info() 加载期间可响应
+    assert time.time() - started < LOAD_DELAY
+    assert session.info()["status"] == "loading"
+    assert _wait_for_status(session, "ready")
+    info = session.info()
+    assert info["loaded"] is True
+    assert info["status"] == "ready"
+    assert info["model_name"] == "/models/qwen"
+
+
+def test_second_load_while_loading_deduped(stub_llamafactory) -> None:
+    session = InferenceSession()
+    r1 = session.load("/models/a")
+    r2 = session.load("/models/b")
+    assert r2["status"] == "loading"
+    assert r2["request_id"] == r1["request_id"]
+    assert _wait_for_status(session, "ready")
+    assert session.info()["status"] == "ready"
+
+
+def test_load_error_surfaces_in_status(stub_failing_llamafactory) -> None:
+    session = InferenceSession()
+    session.load("/models/bad")
+    assert _wait_for_status(session, "error")
+    assert "boom" in session.info()["error"]
+
+
+def test_unload_while_loading_cancels(stub_llamafactory) -> None:
+    session = InferenceSession()
+    session.load("/models/qwen")
+    result = session.unload()
+    assert result["status"] == "cancelling"
+    assert _wait_for_status(session, "idle")
+
+
+def test_chat_while_loading_returns_loading_error(stub_llamafactory) -> None:
+    session = InferenceSession()
+    session.load("/models/qwen")
+    out = session.chat([{"role": "user", "content": "hi"}])
+    assert "still loading" in (out.get("error") or "")
+    assert _wait_for_status(session, "ready")
+    out = session.chat([{"role": "user", "content": "hi"}])
+    assert out.get("response") == "hello from model"
+
+
+def test_chat_stream_while_loading_yields_error(stub_llamafactory) -> None:
+    session = InferenceSession()
+    session.load("/models/qwen")
+    chunks = list(session.chat_stream([{"role": "user", "content": "hi"}]))
+    assert any("still loading" in c for c in chunks)