cli: make bundled help self-describing

packages/inbox-runtime/internal/cli/inbox/cancel.go

@@ -22,6 +22,12 @@ func newCancelCmd(root *rootOptions) *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "cancel",
 		Short: "Cancel a thread",
+		Long: helpLong(
+			"Use cancel to terminate a thread and record a control message explaining why it should stop.",
+			"cancel is usually a leader or operator action rather than a normal worker completion step.",
+			"Use a reason when you need later readers to understand why the thread was stopped.",
+		),
+		Example: `  inbox --db .agents/coord.db cancel --agent leader --thread thr_123 --reason "Task superseded by a new plan."`,
 		RunE: func(cmd *cobra.Command, args []string) error {
 			ctx := cmd.Context()