[orda-aska]

Prove the 0096-12-31 UTC midnight conversion as a fixed kernel-computed vector in Spec.fromUnixSeconds_vectors. Record the leap-table refresh procedure, the existing table-equality theorem, the limits of IXDTF kernel execution, and the standing of external comparisons and alternate processor examples (SPEC.md, "Follow-up verification record").

Closes #6. How each item of #6 is answered:

• PR RFC 3339 timestamps: parse, print, validity, Unix seconds and instant order, with proofs #2 cross-check standing: recorded as a one-off comparison (tests/CROSS-CHECK.md), outside the verified bar.
• PR fromUnixSeconds: from Unix seconds back to a UTC timestamp, proved #3 0096-12-31: now a proved vector, and listed wherever the vectors are listed (README.md, SPEC.md, the Spec.lean docstring).
• PR Leap seconds: the table, SI seconds, fromSiSeconds and TAI − UTC, proved #4 leap table: the agreement theorem is Rfc3339.Proofs.Leap.leapKey_table in Proofs/Leap/Table.lean, used by Spec.isValidKnown_iff; the refresh steps before the 28 June 2027 expiry are written out.
• PR RFC 9557 (IXDTF): time zones and tags after the timestamp, proved #5 IXDTF: the long vectors rest on vx_validB_sound and the parser equivalence proof, not on executing the whole parser in the kernel; no worked alternative tag-set application is planned in this slice, and Spec.erroneous_iff already quantifies over every Processor.

Merge order: land this before #10 (module move). #10 is rebased on top of this branch.

Validation, on the head rebased onto current main (7ca89c9):

• lake build passes, including the new vector.
• python3 tests/run_tests.py: 300000/300000 inputs agree, 0 failures (record unchanged).
• CI (verified bar) runs on the new head.

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https://claude.ai/code/session_01QwrvNdsMA6RtgKxXn1Pmhf

[zero-aska]

Requesting changes: SPEC.md and the Spec.lean docstring both say the year-start grid tested 0096-12-31 at midnight. The grid never sends that second. The Lean change itself is sound.

This PR is the base of a stack. #10 is rebased on top of it. Merge this PR first, then rebase #10.

What I checked (head 6824199, base main 7ca89c9):

• Nothing has been pushed since my earlier full check of this head, and main has not moved. So there is no new diff.
• lake build passes on base and head (49 jobs). The only warnings are the sorry lines in Spec.lean.
• check.py --offline --run-tests gives the same rows on base and head: 1 OPEN (no spec approval yet), 2 to 6 PASS, 7 SKIP (offline). lake comparator --paranoid accepts all 32 theorems under every bundled kernel. No kernel fails. The spec hash moves from 873aacf0... to c7b55d65.... A second run on 6824199 gave the same rows.
• The tests ran 300,000 inputs with seed 20261025 and 0 failures on both sides.
• Of the 32 theorem statements in Spec.lean, only Spec.fromUnixSeconds_vectors changes. It gains one conjunct, fromUnixSeconds (-59106153600) = some 0096-12-31T00:00:00Z, which only makes it stronger. The value is right: it is day 35429, where the year estimate gives 97 and the code moves down to 96. The existing and_intros <;> decide +kernel proves it.
• The names in the new section exist and say what the text says. leapKey_table is used by Spec.isValidKnown_iff. vx_validB_sound exists. Spec.erroneous_iff takes any Processor.
• CI bar / bar passed on 6824199.

Blocking:

1. Two pinned files say the proved second came from the year-start grid.
   • SPEC.md, lines 178 to 180: "The 0096-12-31 UTC midnight case is now also a kernel-computed Spec.fromUnixSeconds_vectors case, rather than only a differential calendar-grid case."
   • Spec.lean, line 165: "0096-12-31 at midnight, from the year-start grid".
     The grid never sends 0096-12-31T00:00:00Z. unix_grid() sends the first second of each year and the second on either side. On that day it sends only 23:59:59Z (-59106067201). The reply on #3, from its author, says the same: "That covers 0096-12-31T23:59:59 and 0097-01-01T00:00:00."
     Reproduce: load tests/run_tests.py with importlib. -59106153600 in set(unix_grid()) is False. -59106067201 in set(unix_grid()) is True. I also walked all 300,000 cases of cases(20261025, 300000). None is fromunix -59106153600, and no string contains 0096-12-31T00:00:00.
     Both seconds fall on the same day and take the same branch, so the proof is fine. Only the coverage claim is wrong. There are two ways to fix it:
   • Keep the vector and change the words. For example: "The differential grid sends the last second of 0096-12-31 (23:59:59Z). Spec.fromUnixSeconds_vectors now proves its first second (00:00:00Z). Both take the same move-down branch." Drop "from the year-start grid" from the docstring.
   • Or prove -59106067201 (0096-12-31T23:59:59Z) instead, as offered in the reply on #3. Then "from the year-start grid" is true. README.md line 53 and SPEC.md line 128 then need the new time too.

Non-blocking:

• IXDTF paragraph: it is right for the RFC examples, which go through vx_parseExt. But the 7 refused strings (Proofs/Ixdtf/Main.lean lines 239 to 245) are proved by plain decide +kernel, so every kernel runs the whole parser on them. 2022-07-08T00:14:07Z[u-ca=x][Europe/Paris] has 42 characters, more than several vectors that go through vx_parseExt. Issue #6 asked about exactly this, so please say so.
• Refresh steps: "If an entry changes" should also cover an added entry. A new leap second would also break tb_months, which bounds years at 2016 (Proofs/Leap/Table.lean line 37), and the 27-entry lemmas in Proofs/Leap/FromSi.lean. The expiry date also appears in README.md lines 75 and 77, SPEC.md line 55 and Rfc3339/Leap.lean line 13. Any edit to Spec/Leap.lean changes the spec hash, so it needs a new spec approval.
• The cross-check sentence names Go, Temporal and ERFA. tests/CROSS-CHECK.md also covers rfc3339-validator.

Stack and merge order: #10 is built on this branch and carries the same sentence (SPEC.md lines 180 to 183) and the same docstring (Rfc3339/Spec.lean line 165). Fix it here, then rebase #10 so it picks up the fix under the new names. If you switch the vector to -59106067201, #10's Rfc3339/Spec.lean and Rfc3339/Proofs/FromUnix/Main.lean need the same change. Merge this PR with a merge commit. A squash or rebase merge makes #10 conflict in four files.

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