☂️: Self-transparent, COSE-only ledgers

[maxtropets]

Completion of this umbrella brings us to

• COSE-only signed ledgers with self-transparency capabilities
• fast and clean receipt generation/verification

Self-transparency breakdown (somewhat in order)

• C++ API to verify COSE receipts (COSE receipt verification in C++ API  #7494)
• C++ API to verify self-signing (current identity only) (COSE receipt verification in C++ API  #7494)
• Preload previous service identities on startup (Prefetch COSE endorsements of previous identities #7518)
• Better C++ API to verify self-signing (including any previous identity) (Verify pre-DR self-issued receipts  #7546)
• Code update policy with self-transparency check (Self-transparent code update #7681)

COSE-only breakdown (somewhat in order too)

• COSE-only receipt getter (Extract describe_cose_receipt_v1 into reusable API #7700)
• New snapshot format (with new receipt) (ONLY COSE receipts in snapshots #7711)
  • to be backported: consuming new snapshots (ONLY COSE receipts in snapshots - backport #7712)
• COSE-only signature config (make sure it's one-way) (COSE-only ledgers #7772)
  • to be backported: consuming COSE-only signed entries (not needed, described why in COSE-only ledgers #7772)

Other important things (at least to discuss, at most to resolve)

• Snapshot format change, to include both COSE receipts and previous service identities endorsement chain
  • Maybe goes separate from a snapshot, is an optimisation and detached to a self-contained issue: (Optimise back-endorsement chain handling #7736)
• COSE receipts endpoint (COSE-only ledgers #7772)
• Make COSE back-endorsement chain optional (moved to Revisit historical TX handling #7824)
• Check Create a dedicated endpoint for COSE service identity endorsement verification #6560 (moved to Revisit historical TX handling #7824)
• Maybe blocking-commit dup related, but make sure to get rid of retrying for historical queries (moved to Revisit historical TX handling #7824)