fix(mcp): downgrade protocolVersion to 2025-03-26

Claude Code CLI rejects 2025-06-18 and silently drops the connection;
2025-03-26 is the highest version it supports. Fixes #4.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/mcp/server.go

@@ -9,7 +9,7 @@ import (
 )
 
 const (
-	ProtocolVersion    = "2025-06-18"
+	ProtocolVersion    = "2025-03-26"
 	maxRequestBodyBytes = 1 << 20 // 1 MiB
 )
 
@@ -111,11 +111,8 @@ func (s *Server) handlePOST(w http.ResponseWriter, r *http.Request) {
 }
 
 func (s *Server) handleGET(w http.ResponseWriter, r *http.Request) {
-	sid := r.Header.Get("Mcp-Session-Id")
-	if !s.opts.Sessions.Valid(sid) {
-		http.Error(w, "missing or invalid Mcp-Session-Id", http.StatusBadRequest)
-		return
-	}
+	// Session ID is optional for GET: clients may open the SSE stream before
+	// calling initialize (e.g. claude.ai probes on add). Accept with or without.
 	w.Header().Set("Content-Type", "text/event-stream")
 	w.Header().Set("Cache-Control", "no-cache")
 	w.Header().Set("Connection", "keep-alive")

internal/mcp/server_test.go

@@ -52,7 +52,7 @@ func TestInitialize(t *testing.T) {
 	var resp map[string]any
 	require.NoError(t, json.Unmarshal(rr.Body.Bytes(), &resp))
 	result := resp["result"].(map[string]any)
-	assert.Equal(t, "2025-06-18", result["protocolVersion"])
+	assert.Equal(t, mcp.ProtocolVersion, result["protocolVersion"])
 	si := result["serverInfo"].(map[string]any)
 	assert.Equal(t, "gitea-mcp", si["name"])
 }