feat: filter tools by OpenAPI tag via MCP_TOOLS_TAGS_INCLUDED

Adds a comma-separated tag allowlist alongside the existing name
allowlist. When both are configured a tool must match both (AND).
Unknown names/tags are ignored with a startup warning, and a filter
that resolves to nothing exposes no tools rather than falling back to
all of them. Startup logs the active filters and the exposed tools.

README.md

@@ -83,6 +83,7 @@ OPENAPI_SPEC_URL=https://petstore3.swagger.io/api/v3/openapi.json uv run xmcp
 | `MCP_PORT` | no | `8000` | Listen port for the HTTP transport |
 | `MCP_SERVER_NAME` | no | spec `info.title` | Name advertised by the MCP server |
 | `MCP_TOOLS_INCLUDED` | no | – (all tools) | Comma-separated allowlist of tool names to expose |
+| `MCP_TOOLS_TAGS_INCLUDED` | no | – (all tags) | Comma-separated allowlist of OpenAPI tags to expose |
 | `HTTP_TIMEOUT` | no | `30` | Timeout in seconds for spec fetch and API calls |
 | `LOG_LEVEL` | no | `INFO` | Python log level |
 
@@ -117,19 +118,24 @@ API request, except credential headers such as `Authorization` and `Cookie`.
 MCP clients that support custom transport headers should send the key on every
 request (at least on `tools/call`).
 
-### Tool allowlist
+### Tool allowlists
 
 By default every operation in the OpenAPI document is exposed as an MCP tool.
-Set `MCP_TOOLS_INCLUDED` to a comma-separated list of tool names to expose
-only those:
+Two environment variables can restrict the exposed set; each accepts a
+comma-separated list, and unset or empty disables that filter:
 
 ```sh
+# Only these operations
 MCP_TOOLS_INCLUDED=getPetById,findPetsByStatus
+
+# Only operations tagged "pet" in the OpenAPI document
+MCP_TOOLS_TAGS_INCLUDED=pet
 ```
 
-Unset or empty exposes all tools. Names that do not match a generated tool are
-ignored with a startup warning, and the active selection is reported at startup
-(`Tools allowlist active: exposing N of M tool(s): ...`).
+When both are set, a tool must match both filters (name **and** tag). Entries
+that do not match anything are ignored with a startup warning, and the active
+selection is reported at startup
+(`Tool filters active (names: ...; tags: ...): exposing N of M tool(s): ...`).
 
 ### Serving a local spec file