fix: inject MCP tools with stable order

mcp/mcp_test.go

@@ -1,14 +1,25 @@
 package mcp_test
 
 import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
 	"regexp"
+	"slices"
+	"strings"
 	"testing"
+	"time"
 
 	"cdr.dev/slog"
+	"cdr.dev/slog/sloggers/slogtest"
 	"go.uber.org/goleak"
 
 	"github.com/coder/aibridge/mcp"
+	"github.com/mark3labs/mcp-go/server"
 	"github.com/stretchr/testify/require"
+
+	mcplib "github.com/mark3labs/mcp-go/mcp"
 )
 
 func TestMain(m *testing.M) {
@@ -282,3 +293,66 @@ func TestFilterAllowedTools(t *testing.T) {
 		})
 	}
 }
+
+func TestToolInjectionOrder(t *testing.T) {
+	t.Parallel()
+
+	// Setup Coder MCP integration
+	mcpSrv := httptest.NewServer(createMockMCPSrv(t))
+	t.Cleanup(mcpSrv.Close)
+
+	logger := slogtest.Make(t, &slogtest.Options{IgnoreErrors: false}).Leveled(slog.LevelDebug)
+
+	proxy, err := mcp.NewStreamableHTTPServerProxy(logger, "coder", mcpSrv.URL, nil, nil, nil)
+	require.NoError(t, err)
+
+	ctx, cancel := context.WithTimeout(t.Context(), time.Second*30)
+	t.Cleanup(cancel)
+
+	require.NoError(t, proxy.Init(ctx))
+	validateToolOrder(t, proxy)
+
+	mgr := mcp.NewServerProxyManager(map[string]mcp.ServerProxier{
+		"mock": proxy,
+	})
+	require.NoError(t, mgr.Init(ctx))
+	validateToolOrder(t, proxy)
+}
+
+func validateToolOrder(t *testing.T, proxy mcp.ServerProxier) {
+	t.Helper()
+
+	tools := proxy.ListTools()
+	require.NotEmpty(t, tools)
+	require.Greater(t, len(tools), 1)
+
+	// Ensure tools are sorted by name; unstable order can bust the cache and lead to increased costs.
+	sorted := slices.Clone(tools)
+	slices.SortFunc(sorted, func(a, b *mcp.Tool) int {
+		return strings.Compare(a.Name, b.Name)
+	})
+	for i, tool := range tools {
+		require.Equal(t, tool.Name, sorted[i].Name, "tool order is not stable")
+	}
+}
+
+func createMockMCPSrv(t *testing.T) http.Handler {
+	t.Helper()
+
+	s := server.NewMCPServer(
+		"Mock coder MCP server",
+		"1.0.0",
+		server.WithToolCapabilities(true),
+	)
+
+	for _, name := range []string{"coder_list_workspaces", "coder_list_templates", "coder_template_version_parameters", "coder_get_authenticated_user"} {
+		tool := mcplib.NewTool(name,
+			mcplib.WithDescription(fmt.Sprintf("Mock of the %s tool", name)),
+		)
+		s.AddTool(tool, func(ctx context.Context, request mcplib.CallToolRequest) (*mcplib.CallToolResult, error) {
+			return mcplib.NewToolResultText("mock"), nil
+		})
+	}
+
+	return server.NewStreamableHTTPServer(s)
+}

mcp/proxy_streamable_http.go

@@ -89,7 +89,11 @@ func (p *StreamableHTTPServerProxy) Init(ctx context.Context) error {
 }
 
 func (p *StreamableHTTPServerProxy) ListTools() []*Tool {
-	return maps.Values(p.tools)
+	tools := maps.Values(p.tools)
+	slices.SortStableFunc(tools, func(a, b *Tool) int {
+		return strings.Compare(a.ID, b.ID)
+	})
+	return tools
 }
 
 func (p *StreamableHTTPServerProxy) GetTool(name string) *Tool {

mcp/server_proxy_manager.go

@@ -3,6 +3,8 @@ package mcp
 import (
 	"context"
 	"fmt"
+	"slices"
+	"strings"
 	"sync"
 
 	"github.com/coder/aibridge/utils"
@@ -82,6 +84,11 @@ func (s *ServerProxyManager) ListTools() []*Tool {
 	for _, tool := range s.tools {
 		out = append(out, tool)
 	}
+
+	slices.SortStableFunc(out, func(a, b *Tool) int {
+		return strings.Compare(a.ID, b.ID)
+	})
+
 	return out
 }