voice.lassul.us goes away without a redirect, like other retired names
in the zone. There is no gatus check for it (coaxmetal is not alwaysOn).

With the lazy /nix/store in the machine jobs, hestia's drain read every
cache.lassul.us-only input path to mirror it into the GitHub Actions
cache, downloading 375-760 MiB per job through the lazy store and
spending 1-4.5 min uploading to the Actions cache at 2-11 MiB/s (PR 65
run). Those paths are already in cache.lassul.us; niks3 uploads
everything newly built.

upstream-cache-key-names replaces hestia's default list, so it repeats
cache.nixos.org-1 next to cache.lassul.us-1. In the eval job,
filter-drv-closures applies the same keys to the drv closures; members
signed by cache.lassul.us are substituted from there by the later jobs.

The day side now shows what the geostationary satellites see, like
zoom.earth, instead of the base map under white clouds synthesised from
infrared:

- Europe/Africa/Atlantic: MTG (Meteosat-12) rgb_truecolour from EUMETSAT.
rgb_geocolour looks the same by day but renders ~4x slower on the
server and timed out (502) for full 2048 px tiles.
- Americas/Pacific: GOES-East and GOES-West GeoColor from GIBS.
- Asia/Australia: GIBS has no Himawari colour product. Himawari band 3
(red, 10 min) is turned into white cloud over the base map, with the
cloud opacity being the reflectance beyond the ground's own albedo.
The daily VIIRS true colour mosaics were the alternative, but their
clouds are up to a day old, have swath seams of different times and
would not match the IR clouds next to them.

Each source is weighted by how well its satellite sees the point: full
trust up to 62° view zenith, none from 78° (the limb is smeared), and
the more nadir satellite wins in overlaps with cos^8 of the zenith
angle, so seams are soft. Trust also needs the sun not to be in front
of the satellite: looking towards a low sun both MTG (mornings over the
Indian Ocean) and Himawari (evenings) are washed out to a pale band
with straight edges, while a long path with the sun behind the
satellite is fine (Berlin at winter noon). A plain path-length limit
would have dropped the latter. Near the terminator (cosz < 0.2)
GeoColor fades into its purple night blend, so the live imagery fades
out there and the IR clouds over the base map take over as before.
Where it is shown, the synthetic clouds and so their relief shading and
shadows are scaled down, so the real image is not shaded twice.

All live layers (including the IR clouds) now request an explicit TIME,
the render time floored to 10 min: without TIME GIBS served tiles of
one layer from different frames (sun glint cut at a tile edge), and it
makes --time render the imagery of that time, not only the sun. The
TIME is capped at the newest frame the server lists (GIBS
DescribeDomains, EUMETSAT per-layer capabilities), since GIBS answers
an unpublished time with an empty image and EUMETSAT with an error;
MTG true colour stops producing frames while its disk is dark.

GIBS also now and then answers with an empty 1 kB image for a frame it
has (the same request succeeds when repeated), which left a quarter of
the Himawari disk missing, so empty tiles are asked for up to 3 times.

A machine job substituted the whole input closure of the derivations it
builds, e.g. 3.4 GiB for neoprism, of which the builds open a few dozen
MiB. .github/lazy-store.sh now runs before the build: it takes what
`nix build --dry-run` would fetch, collects its closure from the
narinfos of cache.nixos.org and cache.lassul.us (tools.lazy-store),
mounts lazy-store on /nix/store, registers the paths with
`nix-store --load-db` and copies their signatures. The build itself,
ci-build.sh's niks3 push and hestia stay as they were: outputs are
written to the real store dir below the mount, and ci-build.sh's
before/after diff of the store starts after the registration.

If anything fails before the paths are registered, it logs an error,
undoes the mount and exits 0, so the build substitutes eagerly. The FUSE
log and the fetched NARs are printed by an always-run step after the
build.

The eval job builds lazy-store next to niks3 and pushes it, the machine
jobs substitute it. The eval and shared jobs keep the plain store: eval
builds nothing but niks3 and lazy-store, and shared builds package
derivations, which read most of their inputs anyway.

FUSE file system for CI's machine builds, ported from the experiment on
ci-lazy-fuse (.github/exp/lazy-store). It mounts on /nix/store the real
store dir (all writes go there) merged with store paths of
cache.nixos.org and cache.lassul.us, whose metadata comes from their
.ls listings and whose NAR is fetched, checked and unpacked on the first
open() of a file in them; reads go through kernel FUSE passthrough. In
the experiment, rebuilding neoprism's system-units, etc, system-path and
toplevel downloaded 62 MiB instead of the 3,455 MiB of an eager
substitution.

Changes from the experiment:
- closure takes the store paths to make valid on stdin (what
`nix build --dry-run` would fetch) instead of walking derivations, and
leaves out paths whose closure is not entirely in the caches, so that
nix never sees a valid path with a missing reference; nix substitutes
those as usual.
- closure also writes the fetched narinfos as a file:// binary cache:
`nix-store --load-db` registers no signatures, and niks3's
--ignore-upstream-key and hestia's upstream-cache-filter go by the
signatures in the local database, so without them both would upload
(and thereby download) every cache.nixos.org path in an output's
closure. `nix store copy-sigs` adds them from there.
- mount fails if a path has no listing instead of leaving it out, as
every path gets registered.

Static, so that once it serves /nix/store it loads nothing from there.
A flake package, so CI builds it once and pushes it to cache.lassul.us,
and the jobs substitute it. passthru.tests.fetch covers fetch, closure
and the registration with signatures against a file:// cache.

The GIBS VIIRS_NOAA20_Thermal_Anomalies_375m_All raster shows each
detection as a coarse blob, far bigger than its 375 m footprint at
wallpaper scale, so the fire layer was loud and distracting.

Fetch FIRMS' keyless global 24 h VIIRS CSVs of NOAA-20, NOAA-21 and
Suomi NPP instead (cached, refreshed hourly like the old layer), drop
low-confidence detections and draw each one as an antialiased dot in
screen space through the same forward mapping as the markers: about
1 px at 1080p, growing slightly with the lens zoom, opacity from FRP on
a log scale between 1 and 500 MW. The colour and max blend under the
clouds stay as before.

Mercator at 16:9 only showed about +-71 degrees, cutting off northern
Greenland and the Arctic. The new variant world is plate carrée, north up,
centred on the equator and the home longitude, showing -90..90 degrees
stretched vertically to fill the screen. It replaces mercator in the CLI
--projection choices and the server's variant parameter, without an alias
for the old name. lens and plain are unchanged.

bluetoothd's hostname plugin overrode General.Name (and Class) with the
hostname and chassis, so disable it. bluetooth-pairing set adapter
properties before AutoEnable powered hci0, failed with Not Powered and
failed the switch; wait for Powered first.