feat(mcp): add opt-in request metadata bridge for tool handlers (#5550)

mcp/options.go

@@ -0,0 +1,33 @@
+package mcp
+
+import "net/http"
+
+// RequestMetadataExtractor extracts request metadata for downstream handlers.
+type RequestMetadataExtractor func(*http.Request) RequestMetadata
+
+// McpOption customizes MCP server construction.
+type McpOption interface {
+	apply(*serverOptions)
+}
+
+type mcpOptionFunc func(*serverOptions)
+
+func (f mcpOptionFunc) apply(opts *serverOptions) {
+	f(opts)
+}
+
+type serverOptions struct {
+	requestMetadataExtractor RequestMetadataExtractor
+}
+
+func defaultServerOptions() serverOptions {
+	return serverOptions{}
+}
+
+// WithRequestMetadataExtractor installs an extractor that runs for each incoming
+// MCP HTTP request, and stores the extracted metadata into handler context.
+func WithRequestMetadataExtractor(extractor RequestMetadataExtractor) McpOption {
+	return mcpOptionFunc(func(opts *serverOptions) {
+		opts.requestMetadataExtractor = extractor
+	})
+}