docs(protocols): second-round pass over the schema prose (#719)

[JarryShaw]

• Searched for similar pull requests
• Followed the coding style — lint not run; no code changed (AST guard)
• make test passes, and a test case covers the change
• Added a changelog entry — N/A — centralised in docs(changelog): shared 1.5.0 changelog — long-lived, merges last (#610, #616, #617, #618, #620) #657

What is the purpose of your pull request?

• docs — documentation only

---

Description

Round-two read of all 37 files under pcapkit/protocols/schema/ for #719; 10 changed, 27 left alone. Fixes: claims the code contradicts (EnumMeta naming the wrong class, MH's Pad1 comment saying length 1 while the code sets 0, NoPayload's __init__ rationale, "special-case by name" vs. isinstance), past-tense history in ethernet/hip/pcapng, the IGMP values RFC 7028 §8 gives alongside the MLD ones, two cross-references split across lines, four MH/PCAP-NG attribute comments whose lead phrase rendered as a type, and typos.

Sphinx -n, fresh builds: warnings naming these files drop from 50 to 40 (main → branch), none new. test_docstring_contract.py, tests/project, test_final_enforcement.py and tests/protocols/schema/* pass.

AST guard (docstrings stripped, compared with origin/main):

File	Identical
__init__.py	True
application/httpv2.py	True
internet/hip.py	True
internet/ipv4.py	True
internet/mh.py	True
link/ethernet.py	True
misc/null.py	True
misc/pcapng.py	True
schema.py	True
transport/tcp.py	True

[github-actions]

Coverage: 88.74% (unit tier, Python 3.14, 6f97862dd, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	4	20	4	93.55%
pcapkit/const	18757	1035	2342	846	90.23%
pcapkit/corekit	1874	91	578	22	94.33%
pcapkit/dumpkit	136	0	40	0	100.00%
pcapkit/foundation	2422	143	842	34	92.62%
pcapkit/interface	112	7	40	5	92.11%
pcapkit/protocols	15653	187	3942	162	98.19%
pcapkit/toolkit	487	71	144	3	84.15%
pcapkit/utilities	429	4	122	4	98.55%
pcapkit/vendor	4409	2359	1006	158	42.84%

Per-file detail: the coverage-html artifact of this run.

[JarryShaw]

Cross-review verdict on 6f97862dd: GOOD TO GO (ran on Sonnet; author Opus)

• AST guard: all 10 files are identical to origin/main once bare strings are stripped.
• null.py: schema_final generates an __init__ only when the class does not define one. Probed: NoPayload({}) raises TypeError.
• ethernet.py: _lookup_next_layer writes a resolved ModuleDescriptor back into the registry, and misses are not recorded.
• mh.py:
  • The Pad1 length is set to 0 in post_process.
  • The IGMP/MLD values match RFC 7028 §8 and §5.1.2, fetched.
• ipv4.py: the Quick-Start options inherit type and length from Option rather than re-declaring them.
• tcp.py: ConditionalField is checked by type in both pack and unpack.
• Cross-references: in a full Sphinx -n build, the repointed Protocol._lookup_registry and EnumLookup targets resolve with no warnings.
• Tests: test_docstring_contract, three schema modules and all 22 tests/project modules pass, one module per process.

Non-blocking: the OSPF comment is true but sits under the # Link Layer Protocols heading of __all__. The real fix is to move the names into the application group. That is a code edit, so it will be filed as a follow-up rather than added to this prose-only PR.

UNVERIFIED: the rendered HTML (checked with the dummy builder only), and there is no base-tree Sphinx diff.