Defines the SA-V3-Ext/Int placeholder attribute scheme (external list
owned by the S3 handover spec, internal list for SA routing + internal
S3 usage), the per-egress Regex property for packing/signing selection,
the inverse-regex delete step at true external egress, optional
ingest-time signing with mandatory validation when already signed, and
the S3 JSON-fallback size attribute for suffix-range trailer reads.
CLAUDE.md points future sessions at .claude/memory/ for accumulated
project context (purpose, SA/MR topology, packaging/signing decisions,
open external dependencies) not fully captured elsewhere in the repo.
Ubuntu