PyTCP

Add a new runtime-tunable sysctl knob to PyTCP — the registered policy-tunable equivalent of a Linux net.* sysctl. Invoke when adding a new knob, migrating an existing module-level constant from static to runtime-tunable, or doing a per-package migration sweep of `*__constants.py` policy values. Do NOT invoke for protocol-invariant constants (RFC-pinned wire values, header sizes, IANA codepoints) — those stay as plain module constants.

Author and maintain per-RFC adherence records under docs/rfc/<group>/rfc_XXXX__<name>/ — paragraph-by-paragraph audit of how PyTCP code complies with each normative statement, including a parallel test-coverage audit. Invoke when creating a new RFC adherence record, refreshing an existing one after code changes, or filling in the catalog for an RFC that has no record yet.