The fixed-tree loop swallowed every failure at Debug and never touched health, so a
driver serving only FIXED: tags (Identity/Axes/Program/Status, the typical FOCAS shape)
read Healthy on /hosts with every node Bad and the #527 watchdog could never fire.
The fixed tree is now a third health path beside the value and alarm paths, combined in
GetHealth (worst state, latest LastSuccessfulRead):
- an answered bootstrap / axis pass clears the device's failure and advances
LastSuccessfulRead;
- a transport failure degrades the driver once the device has been silent past the
same staleness budget that turns its values Bad (from its last answer, or from loop
start when it never answered), with LastSuccessfulRead frozen;
- a CNC refusal (non-OK rc) is not a comms loss: it clears the failure and credits nothing.
Refs #740
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty