[lldb] Document MCP support in LLDB (#145935)

Document how to use MCP support in LLDB. I expect this to change
significantly as the feature matures. For now it covers configuring the
server and two example clients.

lldb/docs/index.rst

@@ -135,6 +135,7 @@ interesting areas to contribute to lldb.
    use/ondemand
    use/aarch64-linux
    use/symbolfilejson
+   use/mcp
    use/troubleshooting
    use/links
    Man Page <man/lldb>

lldb/docs/use/mcp.md

@@ -0,0 +1,85 @@
+# Model Context Protocol (MCP)
+
+LLDB supports the [Model Context Protocol][https://modelcontextprotocol.io]
+(MCP). This structured, machine-friendly protocol allows AI models to access
+and interact with external tools, for example debuggers. Using MCP, an AI agent
+can execute LLDB commands to control the debugger: set breakpoints, inspect
+memory, step through code. This can range from helping you run a specific
+command you cannot immediately remember, to a fully agent-driven debugging
+experience.
+
+## MCP Server
+
+To start the MCP server in LLDB, use the `protocol-server start` command.
+Specify `MCP` as the protocol and provide a URI to listen on. For example, to
+start listening for local TCP connections on port `59999`, use the following
+command:
+
+```
+(lldb) protocol-server start MCP listen://localhost:59999
+MCP server started with connection listeners: connection://[::1]:59999, connection://[127.0.0.1]:59999
+```
+
+The server will automatically stop when exiting LLDB, or it can be stopped
+explicitly with the `protocol-server stop` command.
+
+```
+(lldb) protocol-server stop MCP
+```
+
+The commands will fail if a server is already running or not running
+respectively.
+
+## MCP Client
+
+MCP uses standard input/output (stdio) for communication between client and
+server. The exact configuration depends on the client, but most applications
+allow you to specify an MCP server as a binary and arguments. This means that
+you need to use something like `netcat` to connect to LLDB's MCP server and
+forward communication over stdio over the network connection.
+
+```
+┌──────────┐               ┌──────────┐               ┌──────────┐
+│          │               │          │               │          │
+│   LLDB   ├─────socket────┤  netcat  ├─────stdio─────┤MCP Client│
+│          │               │          │               │          │
+└──────────┘               └──────────┘               └──────────┘
+```
+
+Configuration example for [Claude Code][https://modelcontextprotocol.io/quickstart/user]:
+
+```json
+{
+  "mcpServers": {
+    "tool": {
+      "command": "/usr/bin/nc",
+      "args": ["localhost", "59999"]
+    }
+  }
+}
+```
+
+Configuration example for [Visual Studio Code][https://code.visualstudio.com/docs/copilot/chat/mcp-servers]:
+
+```json
+{
+  "mcp": {
+    "servers": {
+      "lldb": {
+        "type": "stdio",
+        "command": "/usr/bin/nc",
+        "args": ["localhost", "59999"]
+      }
+    }
+  }
+}
+```
+
+### Troubleshooting
+
+The MCP server uses the `Host` log channel. You can enable logging with the
+`log enable` command.
+
+```
+(lldb) log enable lldb host
+```