feat(capability/mcp): MCP 客户端（stdlib JSON-RPC over stdio/SSE）+ Registry 自动注册/Unregister（registry 增 Remove）

internal/capability/mcp/tool.go

@@ -0,0 +1,63 @@
+package mcp
+
+import (
+	"context"
+	"strings"
+)
+
+// mcpTool adapts an MCP tool to the pkg/plugins/sdk Tool interface so it can be
+// registered and invoked like any built-in tool. It is immutable and safe for
+// concurrent use.
+type mcpTool struct {
+	client *Client
+	info   ToolInfo
+}
+
+// Name returns the MCP tool identifier.
+func (t *mcpTool) Name() string {
+	return t.info.Name
+}
+
+// Description returns the MCP tool description.
+func (t *mcpTool) Description() string {
+	return t.info.Description
+}
+
+// Parameters returns the MCP tool input schema, defaulting to an empty object
+// schema when the server omits one.
+func (t *mcpTool) Parameters() (map[string]any, error) {
+	if t.info.InputSchema == nil {
+		return map[string]any{"type": "object", "properties": map[string]any{}}, nil
+	}
+	return t.info.InputSchema, nil
+}
+
+// Execute invokes the MCP tool and returns its concatenated text content.
+func (t *mcpTool) Execute(ctx context.Context, args any) (any, error) {
+	res, err := t.client.CallTool(ctx, t.info.Name, args)
+	if err != nil {
+		return nil, err
+	}
+	return contentText(res.Content), nil
+}
+
+// contentText concatenates the text blocks of a tool result into a single
+// string, ignoring non-text blocks.
+func contentText(content []ContentBlock) string {
+	var b strings.Builder
+	for _, blk := range content {
+		if blk.Type == "" || blk.Type == "text" {
+			b.WriteString(blk.Text)
+		}
+	}
+	return b.String()
+}
+
+// toContentBlocks converts wire content blocks to the public content block type.
+func toContentBlocks(wire []contentBlock) []ContentBlock {
+	out := make([]ContentBlock, 0, len(wire))
+	for _, c := range wire {
+		out = append(out, ContentBlock{Type: c.Type, Text: c.Text})
+	}
+	return out
+}