Add scm_revision to project updates and cleanup

Add validation around prompted scm_branch requiring
  project allow_override field to be true

Updated related process isolation docs

Fix invalid comarision in serializer

from PR review, clarify pre-check logging, minor docs additions

docs/prompting.md

@@ -20,6 +20,7 @@ The standard pattern applies to fields
  - `limit`
  - `diff_mode`
  - `verbosity`
+ - `scm_branch`
 
 ##### Non-Standard Cases