refactor!: replace mcp-go with the official MCP Go SDK

- Swap the mark3labs MCP dependency for modelcontextprotocol/go-sdk v1.7.0
- Add a declarative tool definition and JSON Schema builder to the tool package
- Adapt registered tools to the official low-level handler, recovering panics and mapping failures to JSON-RPC errors
- Narrow tool handlers to take a plain argument map instead of an SDK request type
- Rewire stdio and HTTP transports onto the official server, moving Authorization parsing into receiving middleware
- Add a golden contract test that locks the exposed tool schemas, plus SDK integration and helper tests
- Add a test target and run it in the pull request workflow

BREAKING CHANGE: The exported helpers change signature. Tool.RegisterRead and
Tool.RegisterWrite now take tool.ServerTool instead of server.ServerTool, and the
annotation constructors return *mcp.ToolAnnotations from the official SDK. Callers
must build tool definitions with tool.NewDefinition and handlers with the
func(context.Context, map[string]any) signature.

The 30-second SSE heartbeat is removed because the official SDK has no equivalent.
ServerOptions.KeepAlive is deliberately not used as a substitute, since it sends MCP
ping requests and ping is removed in protocol 2026. HTTP stays stateless=false, so
new clients negotiate at most 2025-11-25.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pkg/tool/definition.go

@@ -0,0 +1,110 @@
+package tool
+
+import "github.com/modelcontextprotocol/go-sdk/mcp"
+
+// Property describes one property in a tool's input schema.
+type Property struct {
+	name     string
+	schema   map[string]any
+	required bool
+}
+
+// PropertyOption configures one property in a tool's input schema.
+type PropertyOption func(map[string]any)
+
+// NewDefinition builds a tool definition without enabling SDK-side validation.
+func NewDefinition(name, description string, annotations *mcp.ToolAnnotations, properties ...Property) *mcp.Tool {
+	inputProperties := make(map[string]any, len(properties))
+	required := make([]string, 0, len(properties))
+	for _, property := range properties {
+		inputProperties[property.name] = property.schema
+		if property.required {
+			required = append(required, property.name)
+		}
+	}
+
+	inputSchema := map[string]any{
+		"type":       "object",
+		"properties": inputProperties,
+	}
+	if len(required) > 0 {
+		inputSchema["required"] = required
+	}
+
+	return &mcp.Tool{
+		Name:        name,
+		Description: description,
+		Annotations: annotations,
+		InputSchema: inputSchema,
+	}
+}
+
+func String(name string, options ...PropertyOption) Property {
+	return newProperty(name, "string", false, options...)
+}
+
+func Number(name string, options ...PropertyOption) Property {
+	return newProperty(name, "number", false, options...)
+}
+
+func Boolean(name string, options ...PropertyOption) Property {
+	return newProperty(name, "boolean", false, options...)
+}
+
+func Array(name string, options ...PropertyOption) Property {
+	return newProperty(name, "array", false, options...)
+}
+
+func Object(name string, options ...PropertyOption) Property {
+	return newProperty(name, "object", true, options...)
+}
+
+func newProperty(name, propertyType string, object bool, options ...PropertyOption) Property {
+	schema := map[string]any{"type": propertyType}
+	if object {
+		schema["properties"] = map[string]any{}
+	}
+	for _, option := range options {
+		option(schema)
+	}
+
+	required, _ := schema["required"].(bool)
+	delete(schema, "required")
+	return Property{name: name, schema: schema, required: required}
+}
+
+func Required() PropertyOption {
+	return func(schema map[string]any) {
+		schema["required"] = true
+	}
+}
+
+func Description(description string) PropertyOption {
+	return func(schema map[string]any) {
+		schema["description"] = description
+	}
+}
+
+func Enum(values ...string) PropertyOption {
+	return func(schema map[string]any) {
+		schema["enum"] = values
+	}
+}
+
+func Default(value any) PropertyOption {
+	return func(schema map[string]any) {
+		schema["default"] = value
+	}
+}
+
+func Minimum(value float64) PropertyOption {
+	return func(schema map[string]any) {
+		schema["minimum"] = value
+	}
+}
+
+func Items(schema any) PropertyOption {
+	return func(propertySchema map[string]any) {
+		propertySchema["items"] = schema
+	}
+}