chore(align): sync Git with running container as authoritative source

Standards alignment (STANDARDS_AUDIT_2026-07-24): Phase 1 标准化核心 +
Phase 2 质量层 landed in the running container and captured in Git so the
three sources (container := image := Git) agree.

Backend (Phase 1 标准化核心):
- mcp_client.py: replaced hand-rolled JSON-RPC with official `mcp` SDK
  (ClientSession, streamable_http/sse transports, protocol auto-negotiation)
- core/otel.py + core/observability.py: standard OpenTelemetry SDK bridge
  (OTLP gRPC), wired to Grafana Alloy (qihu-aiflow-alloy:4317) which forwards
  metrics to Prometheus; emits aiflow_span_duration_ms / aiflow_span_count
- deployments: Grafana Alloy container + Prometheus remote-write receiver

Backend (Phase 2 质量层):
- core/rag_pipeline.py: standardized RAG (recursive overlap chunking +
  rerank hook) reusing pgvector_search
- core/llm_client.py: SDK-ified LLM + embeddings (aembed/embed) collapsing
  hand-rolled httpx calls; trust_env=False to bypass container proxy

Migrations:
- 018_normalize_marketapp_scene.sql: fixed capability allowlist
  (prevents capability wipe on restart)

Alignment performed 2026-07-24 12:18:51. No deletions; secrets/venv/node_modules/
caches were not touched (tracked-source-only copy).

backend/python/app/core/observability.py

@@ -1,6 +1,6 @@
 """
-Qihu-AIFlow 统一可观测基座 (Phase 2.1)
-=====================================
+Qihu-AIFlow 统一可观测基座 (Phase 2.1 + Phase 1.I OTel 增强)
+=============================================================
 提供贯穿一次请求的全局链路 ID（trace_id）与结构化日志能力，
 为后续重构（上下文引擎、媒体/LLM 成本归因）建立回归基线。
 
@@ -10,13 +10,17 @@ Qihu-AIFlow 统一可观测基座 (Phase 2.1)
   TraceIdFilter 自动注入，调用方无需改动。
 - 不引入第三方依赖（structlog 未安装），自带可选的 JSON formatter。
 
+Phase 1.I 增强：span() 在保持原有日志计时的同时，额外嵌套一个标准 OpenTelemetry
+span（经 app.core.otel 桥接，OTLP 导出到 Grafana）。OTel 失败时自动降级为 no-op，
+绝不改变既有日志行为与请求链路。
+
 使用方式：
     from app.core.observability import set_trace_id, get_trace_id, span
 
     # 在中间件里为每个请求注入：
     set_trace_id(request_id)
 
-    # 在关键调用处打计时 span（自动带 trace_id）：
+    # 在关键调用处打计时 span（自动带 trace_id + OTel span）：
     async with span("chat.send_message", conv_id=conv_id):
         return await _send_message_core(...)
 """
@@ -26,6 +30,8 @@ import uuid
 import json
 from contextvars import ContextVar
 
+from app.core.otel import current_span_cm, record_span_metrics
+
 # ---------------------------------------------------------------------------
 # trace_id：贯穿一次请求（含其内所有子调用/协程）的全局链路 ID
 # ---------------------------------------------------------------------------
@@ -103,10 +109,10 @@ def get_logger(name: str | None = None) -> logging.Logger:
 
 
 # ---------------------------------------------------------------------------
-# span：结构化计时上下文管理器（耗时 + trace_id + 自定义字段）
+# span：结构化计时上下文管理器（耗时 + trace_id + 自定义字段 + OTel 嵌套）
 # ---------------------------------------------------------------------------
 class _Span:
-    """同步/异步通用的计时 span。退出时记录 elapsed_ms 与状态。"""
+    """同步/异步通用的计时 span。退出时记录 elapsed_ms 与状态，并结束嵌套的 OTel span。"""
 
     def __init__(self, name: str, **fields):
         self.name = name
@@ -114,6 +120,7 @@ class _Span:
         self._logger = logging.getLogger("aiflow.span")
         self._start = None
         self.elapsed_ms = 0.0
+        self._otel_cm = None  # 嵌套的 OTel span 上下文管理器
 
     def _enter(self):
         self._start = time.perf_counter()
@@ -121,6 +128,10 @@ class _Span:
             f"SPAN_START {self.name}",
             extra={"span": self.name, "event": "start", "trace_id": get_trace_id(), **self.fields},
         )
+        # OTel 嵌套 span（失败安全：current_span_cm 返回 None 时 no-op）
+        self._otel_cm = current_span_cm(self.name, self.fields)
+        if self._otel_cm is not None:
+            self._otel_cm.__enter__()
         return self
 
     def _exit(self, exc_type, exc, tb):
@@ -137,6 +148,24 @@ class _Span:
                 **self.fields,
             },
         )
+        # 结束嵌套的 OTel span（失败安全）
+        if self._otel_cm is not None:
+            try:
+                from opentelemetry import trace as _ot
+                if exc_type is not None:
+                    self._otel_cm.set_status(
+                        _ot.trace.Status(_ot.trace.StatusCode.ERROR, str(exc_type.__name__))
+                    )
+                else:
+                    self._otel_cm.set_status(_ot.trace.Status(_ot.trace.StatusCode.OK))
+                self._otel_cm.__exit__(exc_type, exc, tb)
+            except Exception:
+                pass
+        # 记录 span 指标（耗时直方图 + 计数），供 Grafana 出图（失败安全）
+        try:
+            record_span_metrics(self.name, self.elapsed_ms, status)
+        except Exception:
+            pass
         return False  # 不吞掉异常
 
     # 同步协议