Policy action getting overwrote by irule

I found the solution. You can find if a pool is already selected.

[LB::server pool] will give you the name of the pool selected (or nothing) for example: /Common/example-com-pool

So the solution in my case to avoid the default case to overwrite what my policy did.

default {
    if { ! ([LB::server pool] starts_with "/Common/") } {
        log local0. "DEBUG – pool not selected"    
        HTTP::respond 301 Location "https://[HTTP::host][HTTP::uri]" 
    }
}

NB: For the random googler coming accros this question you can also catch if a redirect was already performed (by your policy) with this ([catch {HTTP::payload replace 0 0 {}}])