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feat: add Anthropic tool_search_tool_bm25_20251119 for lazy loading #260

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feat: add Anthropic tool_search_tool_bm25_20251119 for lazy loading #260

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77 changes: 77 additions & 0 deletions internal/server/mcp.go
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Original file line number Diff line number Diff line change
Expand Up @@ -300,6 +300,21 @@ func (p *MCPProxyServer) registerTools(_ bool) {
)
p.server.AddTool(retrieveToolsTool, p.handleRetrieveTools)

// tool_search_tool_bm25_20251119 - Anthropic-compatible tool search (lazy loading)
// Claude models are fine-tuned to recognize this specific tool name for on-demand tool discovery.
// Returns tool_reference content blocks per Anthropic's custom implementation format.
// See: https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-search-tool
toolSearchBM25Tool := mcp.NewTool("tool_search_tool_bm25_20251119",
mcp.WithDescription("Search for tools by keyword or description. Use this to find relevant tools before calling them."),
mcp.WithTitleAnnotation("Tool Search (BM25)"),
mcp.WithReadOnlyHintAnnotation(true),
mcp.WithString("query",
mcp.Required(),
mcp.Description("The search query (e.g. 'weather', 'git commit', 'database query')."),
),
)
p.server.AddTool(toolSearchBM25Tool, p.handleToolSearchBM25)

// Intent-based tool variants (Spec 018)
// These replace the legacy call_tool with three operation-specific variants
// that enable granular IDE permission control and require explicit intent declaration.
Expand Down Expand Up @@ -900,6 +915,68 @@ func (p *MCPProxyServer) handleRetrieveTools(ctx context.Context, request mcp.Ca
return mcp.NewToolResultText(string(jsonResult)), nil
}

// handleToolSearchBM25 implements the Anthropic-standard tool search tool
// This tool name (tool_search_tool_bm25_20251119) is fine-tuned into Claude models
// for lazy loading tool discovery. Returns tool_reference content blocks per
// Anthropic's custom implementation format.
// See: https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-search-tool
func (p *MCPProxyServer) handleToolSearchBM25(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
startTime := time.Now()

// Extract session info for activity logging (Spec 024)
var sessionID string
if sess := mcpserver.ClientSessionFromContext(ctx); sess != nil {
sessionID = sess.SessionID()
}
requestID := fmt.Sprintf("%d-tool_search_bm25", time.Now().UnixNano())

query, err := request.RequireString("query")
if err != nil {
p.emitActivityInternalToolCall("tool_search_tool_bm25_20251119", "", "", "",
sessionID, requestID, "error", err.Error(),
time.Since(startTime).Milliseconds(), nil, nil, nil)
return mcp.NewToolResultError(fmt.Sprintf("Missing required parameter 'query': %v", err)), nil
}

// Build arguments map for activity logging
args := map[string]interface{}{"query": query}

// Search using existing BM25 index (limit to 5 per Anthropic standard)
results, err := p.index.Search(query, 5)
if err != nil {
p.logger.Error("Tool search failed", zap.String("query", query), zap.Error(err))
p.emitActivityInternalToolCall("tool_search_tool_bm25_20251119", "", "", "",
sessionID, requestID, "error", err.Error(),
time.Since(startTime).Milliseconds(), args, nil, nil)
return mcp.NewToolResultError(fmt.Sprintf("Search failed: %v", err)), nil
}

// Build tool_reference content blocks (Anthropic custom implementation format)
content := make([]map[string]interface{}, 0, len(results))
for _, result := range results {
content = append(content, map[string]interface{}{
"type": "tool_reference",
"tool_name": result.Tool.Name,
})
}

// Return as JSON array (Claude will parse this)
jsonResult, err := json.Marshal(content)
if err != nil {
p.emitActivityInternalToolCall("tool_search_tool_bm25_20251119", "", "", "",
sessionID, requestID, "error", err.Error(),
time.Since(startTime).Milliseconds(), args, nil, nil)
return mcp.NewToolResultError(fmt.Sprintf("Failed to serialize results: %v", err)), nil
}

// Emit success event
p.emitActivityInternalToolCall("tool_search_tool_bm25_20251119", "", "", "",
sessionID, requestID, "success", "",
time.Since(startTime).Milliseconds(), args, content, nil)

return mcp.NewToolResultText(string(jsonResult)), nil
}

// handleCallToolRead implements the call_tool_read functionality (Spec 018)
func (p *MCPProxyServer) handleCallToolRead(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
return p.handleCallToolVariant(ctx, request, contracts.ToolVariantRead)
Expand Down