fix(ingestion): support GET/SSE on /mcp endpoint for claude.ai compatibility

ingestion/internal/mcp/server.go

@@ -48,6 +48,20 @@ func NewServer(brainDir string, pipelineCfg *pipeline.Config, llm pipeline.Compl
 }
 
 func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// MCP streamable HTTP: GET establishes the SSE stream for server-to-client events.
+	if r.Method == http.MethodGet {
+		w.Header().Set("Content-Type", "text/event-stream")
+		w.Header().Set("Cache-Control", "no-cache")
+		w.Header().Set("Connection", "keep-alive")
+		w.Header().Set("X-Accel-Buffering", "no")
+		w.WriteHeader(http.StatusOK)
+		if f, ok := w.(http.Flusher); ok {
+			f.Flush()
+		}
+		<-r.Context().Done()
+		return
+	}
+
 	var req request
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 		writeError(w, nil, -32700, "parse error")