The W8c picker pinned the device-type ladder to `pickedRows[0].type` for
the entire bucket and walked one ladder for every row. The inline
comment promised per-row resolution against the cached ladder map; the
implementation never delivered it. Today's only caller — the
`SLEEP_DURATION` aggregation in `/api/analytics` — feeds single-type
rows so the gap is latent. Future callers (Coach evidence rollup,
doctor-PDF section, correlations engine) that batch multiple
MeasurementTypes through one picker call would have tested non-matching
rows against the wrong ladder.
Group present device-types per row-type, resolve each type's ladder
from the cache, pick the winning device-type independently per type.
Per-type fall-through covers the case where the user's custom ladder
doesn't enumerate any device-type present for a given row-type.
Cover the multi-type path with two new tests:
- per-row ladder resolution preserves each type's winner
- per-type fall-through when a custom ladder is unreachable
Marc-André Bombeck
db5e07a944