The headers a filter needs before evaluating, decoded from the raw block:
nothing, only agdx.ct, or every entry. None when the block’s structure
does not parse, which the caller reports as a malformed record.
Only the agdx.ct header, for a filter that reads no other header. Every
entry is stepped over, so a block whose structure does not parse still
faults the record, but no other key or value is decoded or checked.
Decode native Iggy header TLVs without changing unknown value kinds. An
entry under a non-text key is stepped over undecoded. A malformed value
under a text key faults the whole record. Entries keep their order, and
the evaluator reads the last entry of a repeated key.