fix: gate manifest sync command behind experiment

Hides the slack manifest sync subcommand and the slack sync alias
from --help, and refuses execution unless the manifest-sync experiment
is enabled. Adds ErrExperimentRequired so the user gets a clear
remediation pointing at the --experiment flag.

Author: mwbrooks

cmd/manifest/sync.go

@@ -4,9 +4,11 @@ import (
 	"github.com/opentracing/opentracing-go"
 	"github.com/slackapi/slack-cli/internal/app"
 	"github.com/slackapi/slack-cli/internal/cmdutil"
+	"github.com/slackapi/slack-cli/internal/experiment"
 	"github.com/slackapi/slack-cli/internal/pkg/manifest"
 	"github.com/slackapi/slack-cli/internal/prompts"
 	"github.com/slackapi/slack-cli/internal/shared"
+	"github.com/slackapi/slack-cli/internal/slackerror"
 	"github.com/slackapi/slack-cli/internal/style"
 	"github.com/spf13/cobra"
 )
@@ -15,14 +17,22 @@ var manifestSyncFunc = manifest.Sync
 
 func NewSyncCommand(clients *shared.ClientFactory) *cobra.Command {
 	cmd := &cobra.Command{
-		Use:   "sync",
-		Short: "Sync the app manifest between project and app settings",
-		Long:  "Compare the local project manifest with app settings, resolve differences, and sync both to the same state.",
+		Use:    "sync",
+		Short:  "Sync the app manifest between project and app settings",
+		Long:   "Compare the local project manifest with app settings, resolve differences, and sync both to the same state.",
+		Hidden: true,
 		Example: style.ExampleCommandsf([]style.ExampleCommand{
 			{Command: "manifest sync", Meaning: "Sync project manifest with app settings"},
 		}),
 		Args: cobra.NoArgs,
 		PreRunE: func(cmd *cobra.Command, args []string) error {
+			if !clients.Config.WithExperimentOn(experiment.ManifestSync) {
+				return slackerror.New(slackerror.ErrExperimentRequired).
+					WithRemediation("Enable the %s experiment with %s",
+						style.Highlight(string(experiment.ManifestSync)),
+						style.CommandText("--experiment manifest-sync"),
+					)
+			}
 			return cmdutil.IsValidProjectDirectory(clients)
 		},
 		RunE: func(cmd *cobra.Command, args []string) error {

cmd/manifest/sync_test.go

@@ -0,0 +1,51 @@
+// Copyright 2022-2026 Salesforce, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package manifest
+
+import (
+	"context"
+	"testing"
+
+	"github.com/slackapi/slack-cli/internal/experiment"
+	"github.com/slackapi/slack-cli/internal/shared"
+	"github.com/slackapi/slack-cli/internal/slackerror"
+	"github.com/slackapi/slack-cli/test/testutil"
+	"github.com/spf13/cobra"
+)
+
+func TestSyncCommand(t *testing.T) {
+	testutil.TableTestCommand(t, testutil.CommandTests{
+		"errors when the manifest-sync experiment is off": {
+			Setup: func(t *testing.T, ctx context.Context, cm *shared.ClientsMock, cf *shared.ClientFactory) {
+				cm.AddDefaultMocks()
+				cf.Config.LoadExperiments(ctx, cf.IO.PrintDebug)
+			},
+			ExpectedError: slackerror.New(slackerror.ErrExperimentRequired),
+		},
+		"passes the experiment gate when manifest-sync is enabled via flag": {
+			Setup: func(t *testing.T, ctx context.Context, cm *shared.ClientsMock, cf *shared.ClientFactory) {
+				cm.AddDefaultMocks()
+				cf.Config.ExperimentsFlag = []string{string(experiment.ManifestSync)}
+				cf.Config.LoadExperiments(ctx, cf.IO.PrintDebug)
+			},
+			// We expect the command to fail downstream of the gate (no app
+			// selected, no SDK config), but NOT with ErrCommandUnavailable —
+			// the gate itself should pass.
+			ExpectedErrorStrings: []string{},
+		},
+	}, func(clients *shared.ClientFactory) *cobra.Command {
+		return NewSyncCommand(clients)
+	})
+}

internal/slackerror/errors.go

@@ -104,6 +104,7 @@ const (
 	ErrDotEnvPlaceholderNotFound                     = "dotenv_placeholder_not_found"
 	ErrDotEnvVarMarshal                              = "dotenv_var_marshal_error"
 	ErrEnterpriseNotFound                            = "enterprise_not_found"
+	ErrExperimentRequired                            = "experiment_required"
 	ErrFailForSomeRequests                           = "failed_for_some_requests"
 	ErrFailToGetTeamsForRestrictedUser               = "fail_to_get_teams_for_restricted_user"
 	ErrFailedAddingCollaborator                      = "failed_adding_collaborator"
@@ -733,6 +734,11 @@ Otherwise start your app for local development with: %s`,
 		Message: "The `enterprise` was not found",
 	},
 
+	ErrExperimentRequired: {
+		Code:    ErrExperimentRequired,
+		Message: "This command requires an experiment to be enabled",
+	},
+
 	ErrFailForSomeRequests: {
 		Code:    ErrFailForSomeRequests,
 		Message: "At least one request was not cancelled",