Two holes in the previous two commits, both found by the same review round.
The per-model write queue keyed on the literal spelling, so the backfill's
legacy casing and a UI save's normalized one opened two queues for one model and
raced exactly as before. It now keys on the folded identity, which is what the
backend resolves by.
A .gguf with no recognizable quant token is labelled by its filename stem, and
v2 storage lowercases that label while the scanner probes with the filename's
own casing. Folding only recognized quant labels therefore left the migrated
entry unreachable for precisely the files that need the stem fallback. The
suffix rule now also accepts a case-insensitive match against the label the
scanner derives for that filename, which keeps an ordinary colon out because the
head still has to be a .gguf. _bare_model_id drops onto the same shared rule
rather than repeating half of it.
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