The MQTT bridge fanned out one Home-Assistant device per node (#898) but
applied the *room-level aggregate* classification to every node — so in a
multi-node setup a node in an empty corner inherited another node's
"present", and `motion_level: "absent"` was mis-mapped to full motion
(the aggregate match fell through `Some(_) => 1.0`).
Each node in the sensing broadcast's `nodes` array already carries its own
`classification` (`motion_level`/`presence`/`confidence`, see
PerNodeFeatureInfo) and RSSI. Now each per-node snapshot reads that node's
own classification, deferring to the room aggregate only for fields a node
omits. Vitals (breathing/heart rate) and person count stay room-level.
Extracted the JSON→VitalsSnapshot mapping into a pure, testable function
(`vitals_snapshots_from_sensing_json`) and added 4 unit tests covering
per-node divergence, partial-field fallback, the no-nodes aggregate path,
and the absent→zero-motion fix.
Supersedes #899, which targeted the right bug but read non-existent fields
(`node["motion_level"]` / `node["status"]` instead of the nested
`node["classification"]` + `stale`).
Verified: builds with `--features mqtt`; new tests pass; full crate unit
suite 432 + 114 passed, 0 failed.
Co-Authored-By: claude-flow <ruv@ruv.net>
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