v0.81b "First Light" Hotfix

USB-level misbehaviour related to the ACE Pro's internal reset cycle could cause sporadic failures mid-print when switching between ACEs on every toolchange. This release works around it by keeping a single connection to the ACE that was active when the print started — the start ACE — and never disconnecting from it for the duration of the print.

Trade-off: during a print, only the start ACE has feed_assist available. Heads on other ACEs print without feed_assist; the extruder pulls the filament directly through the bowden. Validated through several hours of multi-color test prints without visible underextrusion. For unusually long bowden routing or high-friction filament, pick the start ACE deliberately with ACE_SWITCH TARGET=N so your most-used material lives on it. The next major version (v0.82) will lift this restriction.

Bonus: cross-ACE toolchanges no longer pay the ~5–10 second USB disconnect/reconnect cost.

Logging: dedicated state and USB debug logs were significantly expanded for post-mortem analysis after print issues (state_debug / usb_debug in [ace]).