1	import Base
2	import ./ordinary_declaration.bend as C
3	import ./decode_data.bend as D
4	
5	# Trusted schema-author witness, not an unforgeable public constructor.
6	# Decoder describes untrusted DATA validation; no implicit Raw -> P inverse.
7	type Gate<-S:Data,-P:Type,-declaration:C.Declaration<S,P>> is Type:
8	  Transient{}
9	  Persisted{codec:D.Codec,project:P -> P & D.Raw}
10	type Field is Data:
11	  Omitted{name:String}
12	  Saved{name:String,value:D.Raw}
13	def transient(~S:Data,~P:Type,~declaration:C.Declaration<S,P>) -> Gate<S,P,declaration>:
14	  Transient{}
15	def persisted(~S:Data,~P:Type,~declaration:C.Declaration<S,P>,codec:D.Codec,project:P -> P & D.Raw) -> Gate<S,P,declaration>:
16	  Persisted{codec,project}
17	def projected(~P:Type,name:String,observed:P & D.Raw) -> P & Field:
18	  match observed:
19	    case (owner,value):(owner,Saved{name,value})
20	# Static eligibility mirrors TS Gate: export itself does not run its decoder.
21	# This low-level operation consumes Gate; snapshot-leaf reconstructs it from
22	# the retained ordinary declaration for repeated owner-preserving saves.
23	def export_owner(~S:Data,~P:Type,~declaration:C.Declaration<S,P>,gate:Gate<S,P,declaration>,owner:P) -> P & Field:
24	  match gate:
25	    case Transient{}:(owner,Omitted{C.key(~S,~P,declaration)})
26	    case Persisted{_,project}:projected(~P,C.key(~S,~P,declaration),project(owner))