fix(ipv4)!: the TS option zeroes the timestamp slots beyond the pointer on rebuild (#1349)

[JarryShaw]

• Searched for similar pull requests
• Followed the coding style (make pylint, make mypy, make isort) — not run
• make test passes, and a test case covers the change — scoped: every tests/protocols/internet/ module, test_option_roundtrip_unit.py, tests/project
• Added a changelog entry — N/A, added centrally

What is the purpose of your pull request?

• fix — corrects a defect

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Description of your pull request and other information

Closes #1349. TS ts_data covered only pointer - 5 octets, and the rest was a zero-packing PaddingField (schema/internet/ipv4.py:321, :326). As #1319 did for LSR/SSR/RR, ts_data now holds every 32-bit slot. The slots at or beyond the pointer go in the new remaining data field (raw words), also a make() keyword. A paired flag never splits a pair. A pre-specified flag still keeps every whole pair; an odd trailing slot now goes in remaining instead of being dropped.

Breaking: TSOption data gains a required remaining field.

Before → after, from_data option bytes: 440c0500 0000000100000002 → …0000000000000000 / exact; 44100900 000000010000000200000003 → …000000010000000000000000 / exact.

Tests: new test_ipv4_ts_slots_unit.py (3 tests, 6 subtests); with the three source files reverted to origin/main, 8 fail. test_ipv4_unit.py updated in four places: they pinned the removed padding-as-pre-specified-address path or built TSOption without remaining. Results: 41 modules gave 384 passed and 2433 subtests passed. Leg protocols/internet ran 549 tests with 0 failures. tests/project gave 389 passed.

[JarryShaw]

Cross-review verdict on a15053649: GOOD TO GO (Sonnet reviewed; author Opus).

• Repros. Both issue repros now rebuild byte-exactly. The revert proof gives 8 failed, as claimed. I re-ran the new module myself and got 3/0.
• Fuzz. 12,102 random TS options, with all 16 flags, lengths 4–40, pointers 0–44 and the overflow nibbles. The PR regresses no case. Exact round trips go from 153 to 2,962, and rebuild errors from 125 to 0. The 1,324 parse errors left are the same inputs main already rejects. A further ~3,800 make → parse → pack cases raise nothing.
• The removed remainder path. It was dead on the parse path. The only callers were the two unit tests this PR rewrites.
• breaking is justified. TSOption data gains a required remaining field, the same precedent as fix(ipv4): LSR/SSR/RR zero the route slots beyond the pointer on rebuild #1319. Nothing in the library reads its fields. Across the 22 fixture captures, the only info difference from main is remaining=() on options-ipv4.pcap frame 5.
• Test edits. The edits to test_ipv4_unit.py are needed, and the bool-rejection assertions still hold. protocols/internet gives 549/0.

Nit: make() silently drops remaining entries beyond the option's slot count.

The reviewer found two round-trip defects that main already has. I am filing them separately:

• a timestamp that comes back 1 ms off through timedelta;
• a trailing partial slot that is zeroed on rebuild.

It also saw that options-ipv4.pcap frame 7 does not rebuild byte-exactly, on both trees.

[JarryShaw]

Follow-up to the verdict above.

• Two of the three side findings are confirmed on main (66950b1f2) and filed as fix(ipv4): TS rebuild floors a float and loses 1 ms on ~1% of timestamps #1391 (the 1 ms float floor) and fix(ipv4): TS zeroes a trailing 1-3 octet partial slot on rebuild #1392 (the partial trailing slot, which still reproduces at this PR's head). Both are blocked until this PR merges.
• Correction: "frame 7 does not rebuild" was a harness artifact (fix(generators): make_samples builds fixtures from the shared checkout, not the tree it runs in #1343). The reviewer regenerated the fixtures against the shared checkout's stale writer. Generated from main itself, every IPv4 layer of options-ipv4.pcap rebuilds exactly.
• What that check did turn up is a separate defect: SEC normalises a non-conforming termination bit, filed as fix(ipv4): SEC rebuild rewrites a non-conforming Field Termination Indicator #1393.

[github-actions]

Coverage: 89.40% (unit tier, Python 3.14, 4deb00a9f, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	4	20	4	93.55%
pcapkit/const	18791	968	2352	869	90.90%
pcapkit/corekit	2018	88	628	24	94.78%
pcapkit/dumpkit	234	2	84	2	98.74%
pcapkit/foundation	2573	99	910	44	94.63%
pcapkit/interface	112	7	40	5	92.11%
pcapkit/protocols	16268	203	4298	165	98.17%
pcapkit/toolkit	539	74	168	3	84.58%
pcapkit/utilities	429	4	122	4	98.55%
pcapkit/vendor	4409	2342	1006	157	43.25%

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

[JarryShaw]

The red Python 3.x legs are main's, not this diff. test_protocol_make_unit.py::TestMakeRawItems::test_unparsable_raw_item_raises_protocol_error also fails on main at 66950b1f2, where I reproduced it locally. It is a semantic conflict between #1344 and #1352, tracked in #1394, and a fix is in progress. This PR needs a re-run once #1394 lands.