A required: true field in a form extension became a rule on the owner's
model, where its value never exists, so every save of the host form failed,
also for administrators who cannot see the extension. mergedRules now skips
extension fields; liftExtensionValues checks required on the submitted value
for visible extensions only (create: must be sent and not blank; update:
only when sent).
- pact.AdminActionExtension.Form with AdminFormExtension: a fields
document (fields.yaml format plus before:/after:/zone: and a tabs:
list) given as an AdminFS path or YAML bytes, Load and Save hooks,
AdminFormLoad/Save/SaveResult, AdminFormErrors and zone constants
- cabana compileFormExtensions places extension fields at owner
anchors at boot, regrouping an extended form by tab
- save lifts extension values before any owner path and runs Save in
the record's transaction after the owner row; show merges Load
- TestFormExtensionTracer: c after a on a, b gives a, c, b through the
admin API, stored in the contributor's table
