feat: AgentChat streaming UX — answer_chunk typewriter, token/cost display, stop marker, session manage, date dividers

- Backend: token-level streaming via on_delta callback + asyncio.Queue bridge, answer_chunk SSE events; final event carries token_usage with cost_yuan; kimi pricing in cost_estimator
- Frontend: typewriter rendering of answer chunks; token/cost in message meta; abort marks message '已停止' and no longer triggers duplicate non-stream fallback; session pin/delete in dropdown (pinned first); date dividers across days

backend/app/agent_runtime/core.py

@@ -14,6 +14,7 @@ import hashlib
 import json
 import logging
 import time
+import asyncio
 from typing import Any, AsyncGenerator, Callable, Dict, List, Optional, Protocol, TypedDict
 
 from app.agent_runtime.schemas import (
@@ -271,13 +272,23 @@ class AgentRuntime:
 
     def _real_token_usage_payload(self) -> Dict[str, Any]:
         """构造随终态事件下发的真实用量 dict（形状含 total_tokens，供下游/前端与计费消费）。"""
-        return {
+        payload = {
             "prompt_tokens": self._real_usage["prompt_tokens"],
             "completion_tokens": self._real_usage["completion_tokens"],
             "total_tokens": self._real_usage["total_tokens"],
             "llm_calls": self._real_usage["llm_calls"],
             "model": self.config.llm.model,
         }
+        try:
+            from app.services.cost_estimator import estimate_cost_yuan
+            payload["cost_yuan"] = estimate_cost_yuan(
+                payload["model"] or "",
+                payload["prompt_tokens"],
+                payload["completion_tokens"],
+            )
+        except Exception:
+            pass
+        return payload
 
     def _attach_token_usage(self, result: AgentResult) -> AgentResult:
         """将 token 用量摘要附加到 AgentResult。预算启用则用其摘要；否则用真实累计用量。"""
@@ -978,15 +989,36 @@ class AgentRuntime:
             # think 事件：告知前端 Agent 正在思考（让 UI 即时反馈，避免假死感）
             yield {"type": "think", "content": "", "reasoning": None, "iteration": self.context.iteration}
 
-            # 调用 LLM
+            # 调用 LLM（token 级流式：delta 进队列，边下边 yield answer_chunk）
             try:
-                response = await llm.chat(
+                delta_q: asyncio.Queue = asyncio.Queue()
+
+                def _on_delta(text: str) -> None:
+                    try:
+                        delta_q.put_nowait(text)
+                    except Exception:
+                        pass
+
+                chat_task = asyncio.create_task(llm.chat(
                     messages=messages,
                     tools=tool_schemas if has_tools and self.context.iteration == 1 else
                                (tool_schemas if has_tools else None),
                     iteration=self.context.iteration,
                     on_completion=_llm_callback,
-                )
+                    on_delta=_on_delta,
+                ))
+                while True:
+                    try:
+                        piece = await asyncio.wait_for(delta_q.get(), timeout=0.2)
+                        yield {"type": "answer_chunk", "content": piece,
+                               "iteration": self.context.iteration}
+                    except asyncio.TimeoutError:
+                        if chat_task.done():
+                            break
+                while not delta_q.empty():
+                    yield {"type": "answer_chunk", "content": delta_q.get_nowait(),
+                           "iteration": self.context.iteration}
+                response = chat_task.result()
             except Exception as e:
                 err_str = str(e)
                 logger.error("LLM 调用失败 (iteration=%s): %s", self.context.iteration, err_str)
@@ -1803,8 +1835,10 @@ class _LLMClient:
         tools: Optional[List[Dict[str, Any]]] = None,
         iteration: int = 1,
         on_completion: Optional[Callable[[Dict[str, Any]], Any]] = None,
+        on_delta: Optional[Callable[[str], None]] = None,
     ) -> Any:
-        """调用 LLM，主模型失败时自动切换 fallback_llm 重试。"""
+        """调用 LLM，主模型失败时自动切换 fallback_llm 重试。
+        on_delta 提供时启用 token 级流式（仅内容增量，工具调用仍会重组后返回）。"""
         from openai import AsyncOpenAI
         from app.core.config import settings
 
@@ -1822,7 +1856,7 @@ class _LLMClient:
         return await self._do_chat(
             api_key=api_key, base_url=base_url, model=self._config.model,
             messages=messages, tools=tools, iteration=iteration,
-            on_completion=on_completion,
+            on_completion=on_completion, on_delta=on_delta,
         )
 
     async def _do_chat(
@@ -1835,6 +1869,7 @@ class _LLMClient:
         iteration: int = 1,
         on_completion: Optional[Callable[[Dict[str, Any]], Any]] = None,
         _is_fallback: bool = False,
+        on_delta: Optional[Callable[[str], None]] = None,
     ) -> Any:
         from openai import AsyncOpenAI
         from app.core.config import settings
@@ -1883,10 +1918,22 @@ class _LLMClient:
                     tool_calls = None
                 return _CachedMsg()
 
+        # token 级流式：要求增量回调时走 stream=True，末 chunk 带 usage
+        if on_delta:
+            kwargs["stream"] = True
+            kwargs["stream_options"] = {"include_usage": True}
+
         start_time = time.perf_counter()
         last_error = None
+        message = None
+        usage = None
         try:
-            response = await client.chat.completions.create(**kwargs)
+            if on_delta:
+                message, usage = await self._stream_chat(client, kwargs, on_delta)
+            else:
+                response = await client.chat.completions.create(**kwargs)
+                message = response.choices[0].message
+                usage = getattr(response, "usage", None)
         except Exception as e:
             last_error = e
 
@@ -1914,6 +1961,7 @@ class _LLMClient:
                             iteration=iteration,
                             on_completion=on_completion,
                             _is_fallback=_is_fallback,
+                            on_delta=on_delta,
                         )
                 except Exception as ce:
                     logger.error("ReactiveCompact 失败: %s", ce)
@@ -1953,12 +2001,11 @@ class _LLMClient:
                         model=fb_model,
                         messages=messages, tools=tools,
                         iteration=iteration, on_completion=on_completion,
-                        _is_fallback=True,
+                        _is_fallback=True, on_delta=on_delta,
                     )
             raise
 
         latency_ms = int((time.perf_counter() - start_time) * 1000)
-        message = response.choices[0].message
 
         # 缓存写入（仅不用工具时）
         if self._config.cache_enabled and not tools and message.content:
@@ -1966,7 +2013,6 @@ class _LLMClient:
             await _llm_cache_set(ck, message.content, self._config.cache_ttl_ms)
 
         # 提取 token 用量
-        usage = getattr(response, "usage", None)
         prompt_tokens = usage.prompt_tokens if usage else 0
         completion_tokens = usage.completion_tokens if usage else 0
         total_tokens = usage.total_tokens if usage else 0
@@ -1985,3 +2031,61 @@ class _LLMClient:
             })
 
         return message
+
+    @staticmethod
+    async def _stream_chat(client: Any, kwargs: Dict[str, Any], on_delta: Callable[[str], None]) -> Any:
+        """消费 OpenAI 兼容流式响应：逐 delta 回调 on_delta，重组为 message 对象返回。
+
+        返回 (message, usage)：message 为 SimpleNamespace（content/tool_calls/
+        reasoning_content，duck-type 兼容 SDK Message），usage 来自开启
+        stream_options.include_usage 后的末 chunk。
+        """
+        from types import SimpleNamespace
+
+        stream = await client.chat.completions.create(**kwargs)
+        content_parts: List[str] = []
+        reasoning_parts: List[str] = []
+        tool_slots: Dict[int, Dict[str, Any]] = {}
+        usage = None
+
+        async for chunk in stream:
+            if getattr(chunk, "usage", None):
+                usage = chunk.usage
+            if not chunk.choices:
+                continue
+            delta = chunk.choices[0].delta
+            piece = getattr(delta, "content", None)
+            if piece:
+                content_parts.append(piece)
+                try:
+                    on_delta(piece)
+                except Exception:
+                    pass
+            reasoning_piece = getattr(delta, "reasoning_content", None)
+            if reasoning_piece:
+                reasoning_parts.append(reasoning_piece)
+            for tc in (getattr(delta, "tool_calls", None) or []):
+                slot = tool_slots.setdefault(tc.index, {"id": None, "name": "", "arguments": ""})
+                if tc.id:
+                    slot["id"] = tc.id
+                fn = getattr(tc, "function", None)
+                if fn is not None:
+                    if getattr(fn, "name", None):
+                        slot["name"] += fn.name
+                    if getattr(fn, "arguments", None):
+                        slot["arguments"] += fn.arguments
+
+        tool_calls = [
+            SimpleNamespace(
+                id=s["id"], type="function",
+                function=SimpleNamespace(name=s["name"], arguments=s["arguments"]),
+            )
+            for _, s in sorted(tool_slots.items())
+        ] or None
+
+        message = SimpleNamespace(
+            content="".join(content_parts) if content_parts else None,
+            tool_calls=tool_calls,
+            reasoning_content="".join(reasoning_parts) if reasoning_parts else None,
+        )
+        return message, usage