The LossLog callback filtered on `"loss" in logs`. Trainer emits eval under
`eval_loss` with no `loss` key, so every eval record was discarded and
loss-series.json showed zero eval points while the log a metre away carried
`eval_loss: 3.198`. An artefact that omits data which demonstrably exists reads as
"no eval was run" rather than "the collector dropped it", which is the failure mode
that costs someone a re-run.
Collector now accepts either key. Seed 2 gets it from launch; seed 1 is already
running with the old code, so recover_eval_series.py parses the eval records back
out of its log -- the data was printed, not lost -- and the chain runs that
recovery before cutting the generation arms, so the artefact is complete before
anything reads it.
The two seeds therefore differ in logging code but not in training math: the
callback only affects what is recorded, never what is computed, so the weight
trajectories remain comparable. Noting it because a difference between the two
arms whose spread sets the decision threshold is worth stating even when it is
provably inert.
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