[vladwing]

semcode lore -b nvme_tcp_queue --limit 0 aborts with "user-provided comparison function does not correctly implement a total order". Any result set that mixes Date headers that parse with ones that do not can trigger this panic.

sort_emails_by_date() compares parsed dates when both Date headers parse and raw strings otherwise, which is not transitive. With A = "Tue, 01 Jan 2030 00:00:00 +0000", B = "U-not-a-date" and C = "Wed, 01 Jan 2020 00:00:00 +0000", it says A < B and B < C by string but C < A by date. Rust's sort panics when it detects such a comparator.

Sort on a key instead: emails whose date parses come first in time order, the rest follow by raw header, and ties break on the raw header and then on message_id. Same-second emails now come out in the same order on every run, whatever order the query returned them in. The function's signature and its five callers are unchanged. The key is computed once per email, so each Date header is parsed once rather than on every comparison.

The newest-first sort in dig was already a total order; its same-instant ties now break on message_id too.

Both new tests fail on the old comparator. One sorts the A/B/C triple from all six input orders. The other sorts 2,000 emails, a third of them with unparseable dates and most sharing a timestamp, from two fixed permutations, and checks the order and that both permutations give the same result.