[Catalyst] Best way to validate Chained actions?

[Micah Jaffe]

I'm trying to figure out the best[*] way to validate Chained actions  
at various points along the action chain.  By validate, I mean "check  
if the action should proceed or bomb out."  Validation is not the  
same as authentication; I may be logged in but I may not have  
permissions to do certain things.  It may also mean proceeding is not  
possible because there is some bad data introduced in one of the  
links.  Let's take a simple chain where I want to check whether or  
not a user can perform basic CRUD type things on our data.
Given two paths:

/bigthing/<id>
/bigthing/<id>/edit

I was building this chain as:

load-bigthing-data -> check_read -> view
                                  -> check_update -> edit

Now this gets convoluted when I want to act on sub part of bigthing.   
Say we have action paths that resemble something like:

/bigthing/<id>/smallthing/<id_2>
/bigthing/<id>/smallthing/<id_2>/edit

So presumably, I'd try to chain like:

load-bigthing-data -> check_read -> load-smallthing-data -> view  
(that's ok)
                                                          ->  
check_update -> edit (bad)

check_update is chained between check_read and edit, so I either need  
to create a new (duplicated) check_update for smallthing edit or  
preferably come up with something better.

I wasn't very happy with the permissions validation being wedged in  
as a link in this action chain.  I think a better solution might be  
to use attributes and custom Actions, but I'm still trying to wrap my  
head around that possibility.  The best solution would bomb out  
before doing any more processing in further actions (i.e. doing it as  
part of an 'end' action is not preferable).

Thoughts?

thanks,
Micah

[*] Best = laziest to code + cleanest to extent + easiest to understand