Phase 5 Batch 1 (补): mcp/server + 2 Tool (Batch 1 commit 时漏 stage)

上一个 commit (7056657) 漏 add 的 mcp 包文件:
- internal/mcp/server.go (Streamable HTTP Handler)
- internal/mcp/tools/list_clusters.go (发现入口)
- internal/mcp/tools/spark_submit.go (本地 exec 提交)
- internal/mcp/tools/helpers.go (textResult/errResult/encodeJSON)

deps.go / rm.go 已在 Phase 5 Batch 2 一起 commit, 此处不重复。

Co-Authored-By: Claude <noreply@anthropic.com>

internal/mcp/tools/list_clusters.go

@@ -0,0 +1,39 @@
+package tools
+
+import (
+	"context"
+
+	"github.com/mark3labs/mcp-go/mcp"
+)
+
+const ListClustersName = "list_clusters"
+
+// NewListClustersTool returns the schema for the list_clusters MCP Tool.
+func NewListClustersTool() mcp.Tool {
+	return mcp.NewTool(ListClustersName,
+		mcp.WithDescription("List active Spark/YARN clusters configured for the agent. Returns the full Cluster struct (minus auth password) for every active cluster — this is the discovery root: from here the agent knows RM/SHS endpoints, auth flavor, and URL allowlists."),
+	)
+}
+
+// ListClustersHandler lists configured clusters and returns only active ones.
+func (d *Deps) ListClustersHandler(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+	callLog := startToolCall(ctx, d.Logger, ListClustersName, nil)
+	defer callLog.End()
+
+	all, err := d.ClusterRepo.List(ctx)
+	if err != nil {
+		callLog.WithError(err)
+		return errResult("list_clusters: " + err.Error()), nil
+	}
+
+	// task_plan.md specifies active clusters only.
+	active := all[:0]
+	for _, c := range all {
+		if c.IsActive {
+			active = append(active, c)
+		}
+	}
+
+	callLog.WithResult(map[string]any{"count": len(active)})
+	return textResult(encodeJSON(active)), nil
+}