Rebuild the docs around tested examples; shrink README.v2.md to a pitch (#2978)

docs_src/lowlevel/tutorial004.py

@@ -0,0 +1,42 @@
+from mcp_types import (
+    CallToolRequestParams,
+    CallToolResult,
+    ListToolsResult,
+    PaginatedRequestParams,
+    TextContent,
+    Tool,
+)
+
+from mcp.server import Server, ServerRequestContext
+
+SEARCH_BOOKS = Tool(
+    name="search_books",
+    description="Search the catalog by title or author.",
+    input_schema={
+        "type": "object",
+        "properties": {"query": {"type": "string"}, "limit": {"type": "integer"}},
+        "required": ["query", "limit"],
+    },
+    output_schema={
+        "type": "object",
+        "properties": {"matches": {"type": "integer"}, "query": {"type": "string"}},
+        "required": ["matches", "query"],
+    },
+)
+
+
+async def list_tools(ctx: ServerRequestContext, params: PaginatedRequestParams | None) -> ListToolsResult:
+    return ListToolsResult(tools=[SEARCH_BOOKS])
+
+
+async def call_tool(ctx: ServerRequestContext, params: CallToolRequestParams) -> CallToolResult:
+    args = params.arguments or {}
+    data = {"matches": 3, "query": args["query"]}
+    return CallToolResult(
+        content=[TextContent(type="text", text=f"Found 3 books matching {args['query']!r}.")],
+        structured_content=data,
+        _meta={"bookshop/record_ids": ["bk_17", "bk_42", "bk_99"]},
+    )
+
+
+server = Server("Bookshop", on_list_tools=list_tools, on_call_tool=call_tool)