Deduplicate raw MCP text response envelope construction

Agent-Logs-Url: https://github.com/github/gh-aw-mcpg/sessions/a3f06b05-31a7-402c-85b4-9fb0e879b2fc

Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Author: Copilot

internal/mcp/tool_result.go

@@ -156,3 +156,12 @@ func NewErrorCallToolResult(err error) (*sdk.CallToolResult, interface{}, error)
 		},
 	}, nil, err
 }
+
+// BuildMCPTextResponse returns a raw MCP response map with a single text content item.
+func BuildMCPTextResponse(text string) map[string]interface{} {
+	return map[string]interface{}{
+		"content": []map[string]interface{}{
+			{"type": "text", "text": text},
+		},
+	}
+}

internal/mcp/tool_result_test.go

@@ -415,3 +415,18 @@ func TestConvertToCallToolResult_MarshalError(t *testing.T) {
 	assert.Nil(t, result)
 	assert.Contains(t, err.Error(), "failed to marshal backend result")
 }
+
+func TestBuildMCPTextResponse(t *testing.T) {
+	text := `{"permission":"write"}`
+
+	result := BuildMCPTextResponse(text)
+
+	require := require.New(t)
+	assert := assert.New(t)
+
+	content, ok := result["content"].([]map[string]interface{})
+	require.True(ok)
+	require.Len(content, 1)
+	assert.Equal("text", content[0]["type"])
+	assert.Equal(text, content[0]["text"])
+}

internal/proxy/proxy.go

@@ -20,6 +20,7 @@ import (
 	"github.com/github/gh-aw-mcpg/internal/difc"
 	"github.com/github/gh-aw-mcpg/internal/guard"
 	"github.com/github/gh-aw-mcpg/internal/logger"
+	"github.com/github/gh-aw-mcpg/internal/mcp"
 	"github.com/github/gh-aw-mcpg/internal/tracing"
 )
 
@@ -331,12 +332,7 @@ func (r *restBackendCaller) CallTool(ctx context.Context, toolName string, args
 	}
 
 	// Wrap in MCP response format: {content: [{type: "text", text: "..."}]}
-	mcpResp := map[string]interface{}{
-		"content": []map[string]interface{}{
-			{"type": "text", "text": string(body)},
-		},
-	}
-	return mcpResp, nil
+	return mcp.BuildMCPTextResponse(string(body)), nil
 }
 
 // forwardToGitHub sends a request to the upstream GitHub API.

internal/server/system_tools.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 
 	"github.com/github/gh-aw-mcpg/internal/logger"
+	"github.com/github/gh-aw-mcpg/internal/mcp"
 )
 
 var logSys = logger.New("server:system_tools")
@@ -89,14 +90,7 @@ func (s *SysServer) callTool(name string, args map[string]interface{}) (interfac
 
 func (s *SysServer) sysInit() (interface{}, error) {
 	logSys.Printf("Initializing MCPG system with %d servers", len(s.serverIDs))
-	return map[string]interface{}{
-		"content": []map[string]interface{}{
-			{
-				"type": "text",
-				"text": fmt.Sprintf("MCPG initialized. Available servers: %v", s.serverIDs),
-			},
-		},
-	}, nil
+	return mcp.BuildMCPTextResponse(fmt.Sprintf("MCPG initialized. Available servers: %v", s.serverIDs)), nil
 }
 
 func (s *SysServer) listServers() (interface{}, error) {
@@ -105,12 +99,5 @@ func (s *SysServer) listServers() (interface{}, error) {
 		serverList += fmt.Sprintf("%d. %s\n", i+1, id)
 	}
 
-	return map[string]interface{}{
-		"content": []map[string]interface{}{
-			{
-				"type": "text",
-				"text": fmt.Sprintf("Configured MCP Servers:\n%s", serverList),
-			},
-		},
-	}, nil
+	return mcp.BuildMCPTextResponse(fmt.Sprintf("Configured MCP Servers:\n%s", serverList)), nil
 }

internal/server/unified.go

@@ -346,12 +346,7 @@ func (g *guardBackendCaller) callCollaboratorPermission(ctx context.Context, arg
 	}
 
 	// Wrap in MCP response format so the WASM guard can parse it consistently
-	mcpResp := map[string]interface{}{
-		"content": []map[string]interface{}{
-			{"type": "text", "text": string(body)},
-		},
-	}
-	return mcpResp, nil
+	return mcp.BuildMCPTextResponse(string(body)), nil
 }
 
 // buildCircuitBreakers creates per-backend circuit breakers from the configuration.