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photocraft/apps
Dylan M. Taylor 6649b78526 Use chrono instead of hand-rolled UTC conversion (#8234)
* Use chrono for UTC/calendar conversion instead of hand-rolled copies

Replaces the civil_from_days copies behind the app's log timestamp, the
Measurement Log's date/time, and the perf report date with chrono as a
workspace dependency (reusing the version already in the tree). Output formats
are unchanged and pinned by the existing tests. AGENTS.md now says time goes
through chrono.

Follow-up to storytold/cadcraft#1785

* Never panic on a clock outside chrono's range; keep 5-digit years unprefixed

chrono's From<SystemTime> unwraps internally, so a clock past year 262143
panicked. logging::timestamp and analysis_cmds::now_iso now read the duration
since the epoch and go through the fallible DateTime::from_timestamp, reading
an out-of-range or pre-epoch clock as the epoch as the old saturating code
did. All three ISO helpers (timestamp, now_iso, perf::iso_utc) write the year
with {:04} rather than %Y, which prefixes a '+' past year 9999.

Tests cover the far-future and year-10000 cases for timestamp and iso_utc.

* Don't build an unrepresentable SystemTime in the far-future test

UNIX_EPOCH + Duration::from_secs(u64::MAX / 2) overflows Windows'
SystemTime and panicked before timestamp() ran, failing the Windows
test job. Build it with checked_add and only assert where it exists.

* time: preserve old out-of-range date conversion (no epoch fallback)

`DateTime::from_timestamp(...).unwrap_or_default()` silently reset any
instant past chrono's year range to 1970-01-01, changing output the old
hand-rolled Howard-Hinnant code converted exactly (e.g. 10_000_000_000_000 s
was 318857-05-20 17:46:40, not the epoch). Restore the old conversion domain
with a cycle-based helper that routes the calendar through chrono (the
calendar repeats every 400 years = 146_097 days, so month/day/time come from
chrono and only the year is carried in i128, keeping every i64 exact).

- apps/photocraft/src/logging.rs: `timestamp` via `utc_parts`; keep the
  pre-1970 epoch clamp; u64 secs past i64::MAX saturate, not epoch.
- crates/engine/src/analysis_cmds.rs: extract pure `iso_from_unix` (cycle
  based) from `now_iso` so the conversion is tested directly.
- xtask/src/perf.rs: `iso_utc` cycle-based, accepts the full u64 range the
  old code did.

Pinned old outputs in tests:
  logging u64::MAX/2 s -> 292277026596-12-04T15:30:07.000Z (was epoch),
          10_000_000_000_000 s -> 318857-05-20T17:46:40.000Z
  iso_from_unix 10_000_000_000_000 -> 318857-05-20T17:46:40Z,
          -10_000_000_000_000 -> -314918-08-13T06:13:20Z, i64 extremes
  iso_utc u64::MAX -> 584554051223-11-09T07:00:15Z (was epoch),
          10_000_000_000_000 -> 318857-05-20T17:46:40Z

* Don't build a year-318857 SystemTime unchecked in the logging test

Windows' SystemTime only reaches about year 30828, so
UNIX_EPOCH + Duration::from_secs(10_000_000_000_000) panicked before
timestamp() ran and failed the Windows test job. Build it with
checked_add and assert where the platform can hold it. The year-10000
case fits everywhere and stays unconditional.

* Name the 400-year range extension as the one exception to the time rule

The rule said never to hand-roll calendar math, but the range fix
(shifting by whole 400-year Gregorian cycles so dates past chrono's year
range keep their old output) is cycle arithmetic, so the rule and the code
disagreed. The rule now names that exception: the library still computes
month, day and time, and only whole cycles are carried in the year.

* Say the library computes month and day; time-of-day is plain arithmetic

Narrows the range-extension wording: the date library computes the
calendar fields, and splitting seconds into hours, minutes and seconds
is ordinary arithmetic, which is what the code does.
2026-10-22 13:54:10 -04:00
..
2026-10-22 15:38:14 +00:00