app.py had grown three co-resident strata: HTTP/caching plumbing, payload
assembly, and search policy. This moves the payload layer — the four
build_* functions, cal_span clamping, hist_end, PAYLOAD_VER, NullRun and
their helpers — into a new views.py with no web dependencies (pure moves,
public names). app.py keeps routing, ETag/derived-store plumbing, and
page serving; migrate.py imports views instead of reaching into app's
privates.
That import previously constructed the whole FastAPI app and — because
places.start_loading() ran at import time — kicked off a background
GeoNames download from an offline batch script. The index load now hangs
off the app's lifespan hook, so it fires when a server starts, not when
the module is imported (tests, migrate).
New tests: cal_span clamping (months-back default, record bounds, 2-year
cap, inversion), builder shapes (grade window ordering, day obs from the
recent bundle, forecast future-only), a regression test that build_day
degrades to climatology when the recent fetch fails, and a subprocess
layering guard that importing views/migrate pulls in neither FastAPI nor
the app module and starts no index download.
