a rev bump has to actually reach the machines it was bumped for

It did not. pending() short-circuited on available(), and available() was
true for any checkout carrying assets/stadium -- so when REV went to 3 for
the shiny variants, such a machine was never pending, was never asked to
rebuild, and quietly went on serving the old set. ready() was false, so
readPack skipped the save-dir cache and read the shipped normal-only packs:
every shiny Pokemon drawn in its ordinary colours, with nothing on screen
saying why. A driver run sitting at "idle 0/151" for twelve thousand frames
is what surfaced it.

pending() is now keyed on ready(), not available(). A checkout with a ROM
spends one loading screen rebuilding a set it had files for; after that it is
current and never pending again. That was the cost the old short-circuit was
avoiding, and it is worth paying once to make a rev bump mean something.

The other half is the players who imported a ROM through the picker rather
than dropping it in baseroms/. beginFrom builds from the bytes and never
keeps them, so on a rev bump there is no ROM to rebuild from -- and with
available() keyed on ready(), the STADIUM rungs would have vanished off the
options row entirely. usable() now separates "these packs are readable" from
"these packs are current": format and count, deliberately not rev. Stale
packs keep the mode working and keep the rungs offered; only the recolour
waits for a rebuild. Losing the shinies until then is a blemish, losing the
mode is not.

readPack orders the two accordingly: a current cache always wins, a stale one
wins only when there is no shipped set to prefer instead -- so a cache from
an extractor rev we have since fixed cannot shadow good files, while a player
whose only copy IS that cache still gets Pokemon on the field.

Verified by rolling the marker back to rev 2 and launching: ready=false,
usable=true, available=true, pending=true, and the build runs unprompted.

tests/shiny_shots.lua

@@ -58,6 +58,15 @@ return function(game)
   -- unrecoloured Pokemon. Calling begin/step directly is both faster and
   -- honest about what is being tested, which is the extraction, not the
   -- screen that usually triggers it.
+  -- the upgrade question, asked before anything is built: with a stale
+  -- marker on disk, does this machine know it has work to do?
+  U.log(("upgrade check: ready=%s usable=%s available=%s pending=%s rom=%s")
+        :format(tostring(StadiumInstall.ready()),
+                tostring(StadiumInstall.usable()),
+                tostring(StadiumInstall.available()),
+                tostring(StadiumInstall.pending()),
+                tostring(StadiumInstall.romPresent())))
+
   if not StadiumInstall.ready() then
     local ok, err = StadiumInstall.begin()
     U.log(("stadium build: begin=%s %s"):format(tostring(ok), tostring(err or "")))