Self-review pass on ec4a55c1 — applying the standing kettui-grade
rule (see memory/feedback_always_build_kettui_grade.md). Three issues
that would have surfaced on review:
1. Silent tz fallback to UTC
``_resolve_tz`` returned UTC when the IANA name was unknown — no
log, no warning. User on a host without ``tzdata`` who configures
``America/Los_Angeles`` got schedules running silently at UTC
offset with no way to debug. Now logs WARNING once per unknown
name (deduped via ``_UNKNOWN_TZ_WARNED`` set so a misconfigured
row doesn't spam every poll cycle) and the log line names BOTH
real causes — typo or missing tzdata — so the user can fix from
a single grep.
2. ``weeks`` unit drift from engine
I added ``'weeks': 86400*7`` to ``_INTERVAL_MULTIPLIERS`` but the
engine's existing ``_calc_delay_seconds`` only recognises
minutes/hours/days. Until PR 2 collapses both paths through this
function, any row whose config snuck through with ``unit='weeks'``
would get scheduled by the engine as 1-hour and by this function
as 7-day — drift between two live implementations. Dropped
``weeks`` from the map to match the engine. Added a comment
pinning the map to the engine's contract and a regression test
that asserts ``unit='weeks'`` falls back to the same hours
default the engine produces.
3. DST edge cases unverified
The module docstring claims DST-aware via ``zoneinfo`` but no test
pinned the spring-forward gap (02:30 LA on DST-Sunday doesn't
exist) or fall-back ambiguity (01:30 LA on fall-Sunday happens
twice). Three new tests:
- ``test_dst_spring_forward_lands_after_the_gap`` — pins that the
function doesn't crash + lands on a real instant past ``now``.
- ``test_dst_fall_back_handles_ambiguous_local_time`` — pins
zoneinfo's default-earlier-instant resolution for ambiguous
local times (01:30 PDT vs 01:30 PST → picks PDT).
- ``test_weekly_across_dst_boundary_keeps_local_wall_clock`` —
pins that a "every Sunday at 09:00 LA" schedule keeps the
local wall clock across the boundary even though the UTC
equivalent shifts by an hour. This is the exact bug class
that caused the May 2026 "next in 8h" tz mismatch.
Also loosened ``tzdata==2026.2`` to ``tzdata>=2024.1``. IANA tz data
changes a few times a year for real-world DST policy updates; pinning
to one snapshot would freeze the app's tz knowledge to the build date
and miss future government-mandated rule changes.
41 schedule tests pass (5 new); 240 across the full automation suite.
Ruff clean.
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