chore: import upstream snapshot with attribution

docs/run/opentelemetry.md

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+# OpenTelemetry
+
+Your server is already traced. You don't have to add anything.
+
+Every server you create emits an [OpenTelemetry](https://opentelemetry.io/) span for every
+message it handles. You didn't write that, and you don't import it. It is there the moment you
+call `MCPServer(...)`.
+
+```python title="server.py"
+--8<-- "docs_src/opentelemetry/tutorial001.py"
+```
+
+That is a complete, traced server. Call `search_books` and a span is created for it. The same is
+true for the low-level `Server`: the tracing lives on both.
+
+## What you get
+
+Every inbound message becomes a `SERVER` span named after the method and its target. So a
+`tools/call` for `search_books` is the span `tools/call search_books`, and a bare `tools/list`
+is just `tools/list`.
+
+Each span carries a few attributes:
+
+* `mcp.method.name` and `mcp.protocol.version`, on every span.
+* `jsonrpc.request.id`, on a request (a notification has none).
+* A handler that raises sets the span status to error. So does a tool result with `is_error=True`.
+
+And because tracing a tool call is such a common thing to want, `tools/call` spans speak
+OpenTelemetry's [GenAI semantic conventions](https://opentelemetry.io/docs/specs/semconv/gen-ai/):
+
+* `gen_ai.operation.name`, set to `"execute_tool"`.
+* `gen_ai.tool.name`, set to the tool being called.
+
+A `prompts/get` span gets `gen_ai.prompt.name` in the same spirit. The list methods carry no
+`gen_ai.*` keys, because there is nothing to name.
+
+!!! tip
+    Those GenAI attributes are the reason a tracing UI groups your tool calls the way it groups
+    any other agent's. You get that grouping for free, with no extra code.
+
+## It costs nothing until you want it
+
+Here is the part that makes "on by default" a comfortable default.
+
+The SDK depends only on `opentelemetry-api`, the lightweight half of OpenTelemetry. With no SDK
+and no exporter installed, creating a span is a no-op. So the spans your server is emitting right
+now cost you almost nothing, and nobody is collecting them.
+
+The day you want to *see* them, you install the other half and point it somewhere:
+
+```console
+uv add opentelemetry-sdk opentelemetry-exporter-otlp
+```
+
+Configure an exporter the usual OpenTelemetry way, and every span the SDK has been quietly
+creating lights up. Your server code does not change. Not one line.
+
+!!! info
+    [Pydantic Logfire](https://logfire.pydantic.dev/) is one such backend, and it does the
+    configuration for you: `pip install logfire`, `logfire.configure()`, and your MCP spans show
+    up in the live view. It is built on OpenTelemetry, so anything below applies to it too.
+
+## Traces that cross the wire
+
+A trace is most useful when it follows a request from the client into the server, in one
+connected picture.
+
+When the client and the server both run the SDK, that connection is automatic. The client injects
+the [W3C trace context](https://www.w3.org/TR/trace-context/) into the request, and the server
+reads it back out, so the server span nests under the client span in the same trace. This is
+[SEP-414](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/414), and you get it without
+asking.
+
+If the inbound message carries no trace context, for example a request from a client that is not
+the SDK, the server span simply parents to whatever span is already current on the server, rather
+than starting a brand-new orphan trace.
+
+## Turning it off
+
+Tracing is a middleware, the first one on your server's list. If you really want a server that
+emits no spans, take it off:
+
+```python
+from mcp.server._otel import OpenTelemetryMiddleware
+
+mcp._lowlevel_server.middleware[:] = [
+    m for m in mcp._lowlevel_server.middleware if not isinstance(m, OpenTelemetryMiddleware)
+]
+```
+
+!!! warning
+    That import has a leading underscore, and that is on purpose. The class is provisional, the
+    same way [`Server.middleware`](../advanced/middleware.md) is provisional, so the import path is something
+    you should expect to change. You almost never need this: with no exporter installed the spans
+    are free, so the usual answer is to leave them on and not install an exporter.
+
+## Recap
+
+* Every `MCPServer` and every low-level `Server` emits one `SERVER` span per inbound message, out
+  of the box. You write nothing.
+* Spans carry `mcp.method.name` and `mcp.protocol.version`; `tools/call` and `prompts/get` also
+  carry GenAI attributes so your tool calls group like any other agent's.
+* It costs nothing until you install an OpenTelemetry SDK and an exporter, and then it lights up
+  with no change to your server.
+* Client-to-server trace context propagates automatically when both sides run the SDK.
+
+The thing that decides whether a request runs at all is **[Authorization](authorization.md)**.