feat(ingestion): add MCP server skeleton with tools/list

Adds an MCP HTTP handler under ingestion/internal/mcp. Implements
initialize, tools/list, and the JSON-RPC notification skip from prior
work. Tool dispatch is stubbed (returns unknown-tool error) and will be
filled in by subsequent tasks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ingestion/internal/mcp/server.go

@@ -0,0 +1,119 @@
+// Package mcp implements an MCP HTTP handler for the ingestion service.
+// Exposed tools: brain_query, brain_write, brain_ingest, brain_ingest_raw, session_log.
+package mcp
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/pipeline"
+)
+
+type request struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      any             `json:"id"`
+	Method  string          `json:"method"`
+	Params  json.RawMessage `json:"params"`
+}
+
+type response struct {
+	JSONRPC string    `json:"jsonrpc"`
+	ID      any       `json:"id,omitempty"`
+	Result  any       `json:"result,omitempty"`
+	Error   *rpcError `json:"error,omitempty"`
+}
+
+type rpcError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+}
+
+// Server handles MCP JSON-RPC over HTTP for the ingestion service.
+type Server struct {
+	brainDir string
+	pipeline pipeline.Config
+	llm      pipeline.CompleteFunc
+}
+
+// NewServer constructs a Server bound to brainDir. pipelineCfg supplies the
+// LLM-backed pipeline; llm may be nil for non-LLM tools only.
+func NewServer(brainDir string, pipelineCfg *pipeline.Config, llm pipeline.CompleteFunc) *Server {
+	cfg := pipeline.Config{}
+	if pipelineCfg != nil {
+		cfg = *pipelineCfg
+	}
+	return &Server{brainDir: brainDir, pipeline: cfg, llm: llm}
+}
+
+func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	var req request
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, nil, -32700, "parse error")
+		return
+	}
+
+	// JSON-RPC 2.0 notifications (no id) must not receive a response.
+	if req.ID == nil {
+		return
+	}
+
+	var result any
+	var rpcErr *rpcError
+
+	switch req.Method {
+	case "initialize":
+		result = map[string]any{
+			"protocolVersion": "2024-11-05",
+			"capabilities":    map[string]any{"tools": map[string]any{}},
+			"serverInfo":      map[string]any{"name": "ingestion-brain", "version": "0.1.0"},
+		}
+
+	case "tools/list":
+		result = map[string]any{"tools": s.tools()}
+
+	case "tools/call":
+		var p struct {
+			Name      string          `json:"name"`
+			Arguments json.RawMessage `json:"arguments"`
+		}
+		if err := json.Unmarshal(req.Params, &p); err != nil {
+			rpcErr = &rpcError{Code: -32602, Message: "invalid params"}
+			break
+		}
+		out, err := s.handleCall(r.Context(), p.Name, p.Arguments)
+		if err != nil {
+			rpcErr = &rpcError{Code: -32000, Message: err.Error()}
+			break
+		}
+		result = map[string]any{
+			"content": []map[string]any{{"type": "text", "text": string(out)}},
+		}
+
+	default:
+		rpcErr = &rpcError{Code: -32601, Message: "method not found: " + req.Method}
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(response{
+		JSONRPC: "2.0",
+		ID:      req.ID,
+		Result:  result,
+		Error:   rpcErr,
+	})
+}
+
+func writeError(w http.ResponseWriter, id any, code int, msg string) {
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(response{
+		JSONRPC: "2.0",
+		ID:      id,
+		Error:   &rpcError{Code: code, Message: msg},
+	})
+}
+
+// handleCall dispatches a tools/call. Stub for Task 1; expanded in later tasks.
+func (s *Server) handleCall(ctx context.Context, name string, args json.RawMessage) (json.RawMessage, error) {
+	return nil, fmt.Errorf("unknown tool: %s", name)
+}