Article 27 research notes, checked on 2026-09-22 and reviewed on 2026-09-23.

Primary sources:
- RFC 9000 §§2, 5.1, 8.2, 9, 9.4, 12.3, 13.3, QUIC transport:
  https://www.rfc-editor.org/rfc/rfc9000.html
  Used for streams, packet/connection framing, connection IDs, migration, PATH_CHALLENGE/PATH_RESPONSE.
- RFC 9001 §§4, 4.4, 4.6, 9.2, QUIC over TLS:
  https://www.rfc-editor.org/rfc/rfc9001.html
  Used for TLS integration and 0-RTT boundary.
- RFC 9002 §§2, 4, 6, 7, QUIC loss detection and congestion control:
  https://www.rfc-editor.org/rfc/rfc9002.html
  Used for packet number spaces, ACK ranges, loss detection, PTO, congestion control.
- RFC 9114, HTTP/3:
  https://www.rfc-editor.org/rfc/rfc9114.html
  Used only to keep the boundary: HTTP/3 mapping is article 28.

Facts carried into the article:
- Stream-local ordered byte streams do not mean per-stream congestion control.
- QUIC packet numbers are separate from stream offsets.
- Initial, Handshake, and Application Data packet number spaces are distinct; 0-RTT and 1-RTT packets are in the Application Data space.
- PTO arithmetic can be hand-checked; PTO expiry alone is not a claim that the packet is lost or that cwnd is reduced.
- 0-RTT depends on resumption material and server policy; it is not available on a first connection.
- Path validation uses PATH_CHALLENGE/PATH_RESPONSE, and connection IDs help keep connection identity across address changes.
- PTO expiry sends probes but does not itself mark earlier packets lost.
- A newly validated path normally starts with reset congestion and RTT state; a peer port-only change is the specified exception.

Verification boundary:
- No mature QUIC implementation was run in this turn.
- No packet capture, loss-injection, NAT rebinding, path migration, or HTTP/3 comparison was performed.
- handcalc.py checks finite arithmetic examples only.