feat!: support protocol 2026-07-28 over HTTP and add --bind (#227)

Adds MCP protocol `2026-07-28` over HTTP through the official Go SDK, and validates the `Origin` header on every request as the spec requires.

Tool and Gitea failures now come back as an ordinary `tools/call` result carrying `result.isError: true`, the way the SDK's own tool wrapper reports them. Malformed requests, unknown tools or methods, and server faults stay JSON-RPC errors.

Adds `-b, --bind` to narrow the listen address. The default still accepts every interface, so this is opt-in hardening. It matters because a request that omits `Authorization` falls back to the server's own token.

**Breaking: the HTTP endpoint no longer keeps a session per client.** What changes for a client:

1. `/mcp` accepts `POST` only, and answers `405` to `GET` or `DELETE`.
2. The server neither sends nor accepts `Mcp-Session-Id`, so there is no session handshake to perform.
3. There is no standalone SSE stream and no `Last-Event-ID` resumption. If a response stream breaks, send the whole request again under a new JSON-RPC id.

Clients that already speak current streamable HTTP need no changes. Anything relying on the session handshake or the standalone SSE stream should stay on the previous release.

---------

Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/227
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>

pkg/flag/flag.go

@@ -2,6 +2,7 @@ package flag
 
 var (
 	Host    string
+	Bind    string
 	Port    int
 	Token   string
 	Version string

pkg/to/to.go

@@ -25,5 +25,7 @@ func TextResult(v any) (*mcp.CallToolResult, error) {
 
 func ErrorResult(err error) (*mcp.CallToolResult, error) {
 	log.Errorf("%s", err.Error())
-	return nil, err
+	var result mcp.CallToolResult
+	result.SetError(err)
+	return &result, nil
 }

pkg/to/to_test.go

@@ -27,7 +27,16 @@ func TestTextResult(t *testing.T) {
 func TestErrorResult(t *testing.T) {
 	want := errors.New("failed")
 	result, err := ErrorResult(want)
-	if result != nil || !errors.Is(err, want) {
-		t.Errorf("ErrorResult() = (%#v, %v), want (nil, %v)", result, err, want)
+	if err != nil {
+		t.Fatalf("ErrorResult() error = %v", err)
+	}
+	if !result.IsError {
+		t.Error("IsError = false, want true")
+	}
+	if len(result.Content) != 1 {
+		t.Fatalf("len(Content) = %d, want 1", len(result.Content))
+	}
+	if content, ok := result.Content[0].(*mcp.TextContent); !ok || content.Text != want.Error() {
+		t.Errorf("Content[0] = %#v, want text %q", result.Content[0], want)
 	}
 }

pkg/tool/handler_test.go

@@ -68,27 +68,36 @@ func TestMCPHandlerAcceptsAbsentArguments(t *testing.T) {
 	}
 }
 
-func TestMCPHandlerConvertsErrorsAndRecoversPanics(t *testing.T) {
+func TestMCPHandlerErrorClassification(t *testing.T) {
 	for _, test := range []struct {
-		name    string
-		handler Handler
+		name     string
+		handler  Handler
+		wantCode int64
 	}{
 		{
-			name: "handler error",
-			handler: func(context.Context, map[string]any) (*mcp.CallToolResult, error) {
-				return nil, errors.New("failed")
-			},
+			name:     "server error",
+			handler:  func(context.Context, map[string]any) (*mcp.CallToolResult, error) { return nil, errors.New("failed") },
+			wantCode: jsonrpc.CodeInternalError,
 		},
 		{
-			name: "panic",
+			name: "protocol error",
 			handler: func(context.Context, map[string]any) (*mcp.CallToolResult, error) {
-				panic("failed")
+				return nil, &jsonrpc.Error{Code: jsonrpc.CodeInvalidParams, Message: "failed"}
 			},
+			wantCode: jsonrpc.CodeInvalidParams,
+		},
+		{
+			name:     "panic",
+			handler:  func(context.Context, map[string]any) (*mcp.CallToolResult, error) { panic("failed") },
+			wantCode: jsonrpc.CodeInternalError,
 		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
-			_, err := callTool(test.handler, nil)
-			assertProtocolErrorCode(t, err, jsonrpc.CodeInternalError)
+			result, err := callTool(test.handler, nil)
+			if result != nil {
+				t.Errorf("result = %#v, want nil", result)
+			}
+			assertProtocolErrorCode(t, err, test.wantCode)
 		})
 	}
 }

pkg/tool/tool.go

@@ -107,8 +107,7 @@ func (s ServerTool) MCPHandler() mcp.ToolHandler {
 			if errors.As(err, &protocolErr) {
 				return nil, err
 			}
-			// Preserve mcp-go behavior; tool-result errors are a separate change.
-			return nil, internalError(err)
+			return nil, internalError(err) // Expected failures never reach here, handlers use CallToolResult.
 		}
 		return result, nil
 	}