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>

backend/app/modules/compute_gateway/sync.py

@@ -1,15 +1,101 @@
 from __future__ import annotations
 
+import json
+import time
 from typing import Any
 
 from app.db.platform_store import get_platform_store
 from app.modules.compute_gateway.client import ComputeNodeClient
 
+# starting 状态允许的最大轮询次数（约 40 * 3s ≈ 2 分钟），超过即判定节点不可达
+MAX_STARTING_ATTEMPTS = 40
+
 
 def _node_for_task(task: dict[str, Any]) -> dict[str, Any] | None:
     return next((node for node in get_platform_store().compute_nodes() if node["id"] == task.get("compute_node_id")), None)
 
 
+def _parse_inference_load_status(task: dict[str, Any]) -> tuple[list[dict[str, Any]], dict[str, Any]]:
+    load_status = task.get("load_status") or {}
+    if isinstance(load_status, str):
+        try:
+            load_status = json.loads(load_status)
+        except (json.JSONDecodeError, TypeError):
+            load_status = {}
+    return load_status.get("loaded_models") or [], load_status
+
+
+async def reconcile_inference_loads(store: Any) -> list[dict[str, Any]]:
+    """推进处于 starting 状态的推理加载。
+
+    模型加载已改为异步派发：/model-compare/{id}/load 立即返回，这里在每次
+    轮询时查询对应计算节点的 /inference/status，把任务从 starting 推进到
+    ready/error。使用短超时，单节点不可达不会阻塞整轮轮询。
+    """
+    reconciled: list[dict[str, Any]] = []
+    now = time.time()
+    for task in store.compare_tasks():
+        items, _ = _parse_inference_load_status(task)
+        if not any(item.get("status") == "starting" for item in items):
+            continue
+        # dirty 只要处理过任一 starting 项就置位：load_attempts / last_polled_at
+        # 必须落库，否则节点不可达时计数不会累积，封顶逻辑永远触发不了
+        dirty = False
+        for item in items:
+            if item.get("status") != "starting":
+                continue
+            # 节流：同一 item 每 3s 只查询一次
+            if now - float(item.get("last_polled_at") or 0) < 3:
+                continue
+            item["last_polled_at"] = now
+            item["load_attempts"] = int(item.get("load_attempts") or 0) + 1
+            dirty = True
+            node = next((n for n in store.compute_nodes() if n["id"] == item.get("node_id")), None)
+            if not node:
+                item["status"] = "error"
+                item["error"] = "compute node deleted"
+                store.mark_inference_unloaded(item.get("node_id") or "")
+                continue
+            if not node.get("enabled") or node.get("scheduler_status") != "online":
+                item["status"] = "error"
+                item["error"] = "compute node offline"
+                store.mark_inference_unloaded(node["id"])
+                continue
+            try:
+                status = await ComputeNodeClient(node["api_base_url"]).inference_status()
+            except Exception as exc:  # noqa: BLE001 - node unreachable; keep retrying until cap
+                if int(item.get("load_attempts") or 0) >= MAX_STARTING_ATTEMPTS:
+                    item["status"] = "error"
+                    item["error"] = f"compute node unreachable: {exc}"
+                    store.mark_inference_unloaded(node["id"])
+                continue
+            node_status = status.get("status")
+            if node_status == "ready":
+                item["status"] = "ready"
+                item.pop("error", None)
+                store.mark_inference_loaded(node["id"])
+            elif node_status == "error":
+                item["status"] = "error"
+                item["error"] = status.get("error") or "model load failed on compute node"
+                store.mark_inference_unloaded(node["id"])
+            elif node_status == "idle":
+                # 节点重启导致已加载模型丢失
+                item["status"] = "error"
+                item["error"] = "model disappeared from compute node (node may have restarted)"
+                store.mark_inference_unloaded(node["id"])
+            # node_status == "loading" -> 保持 starting，下轮再查
+        if dirty:
+            if any(i.get("status") in {"ready", "running"} for i in items):
+                new_status = "loaded"
+            elif any(i.get("status") == "starting" for i in items):
+                new_status = "starting"  # 仍在加载中，保持 starting
+            else:
+                new_status = "failed"
+            store.update_compare_task(task["id"], {"status": new_status, "load_status": {"loaded_models": items}})
+            reconciled.append({"task_id": task["id"], "status": new_status})
+    return reconciled
+
+
 async def fetch_eval_result_content(client: ComputeNodeClient, node: dict[str, Any], job: dict[str, Any]) -> dict[str, Any] | None:
     output_dir = job.get("output_dir")
     if not output_dir:
@@ -95,5 +181,13 @@ async def poll_compute_jobs_once() -> dict[str, Any]:
         except Exception as exc:  # noqa: BLE001
             failed.append({"eval_task_id": eval_task["id"], "error": str(exc)})
 
+    # ── Inference load reconciliation ─────────────────────────────────────
+    try:
+        inference_reconciled = await reconcile_inference_loads(store)
+    except Exception as exc:  # noqa: BLE001 - keep polling alive
+        failed.append({"inference_reconcile": str(exc)})
+        inference_reconciled = []
+
     return {"synced": len(synced) + len(standalone_synced) + eval_synced, "failed": failed,
-            "items": synced, "standalone": standalone_synced, "eval_synced": eval_synced}
+            "items": synced, "standalone": standalone_synced, "eval_synced": eval_synced,
+            "inference_reconciled": inference_reconciled}