app: fault handling: lost adapter ends the session, position is the default mode, latched faults say how to clear

[aq1018]

Three things the bench pass showed when something goes wrong, each with a way out now.

• An unplugged adapter ends the session. The manager's failure path recognises the disconnect class and reports it once; the session detaches the bus, releases the client and enters a new lost status. The browser's USB disconnect event takes the same path so an idle bus notices at once. The sidebar reads Connection lost, the popover gives the reason in plain words and a Reconnect button that reuses the permitted adapter without a chooser.
• Position is the app's default mode and the app owns it: the select's value is a stored preference, written to the servo once whenever the servo reports something else, so a reboot or factory reset back to open loop is corrected. A mode write is not torque-gated in the firmware, so no torque dance is needed.
• Latched faults say how to clear: every fault statement on the Health card ends with the torque off and on instruction (the firmware's only fault acknowledge), a Clear fault button appears while a fault is latched and does the toggle inside one bus turn, and the Live cluster shows one warning line under the torque switch until the fault is gone.

Specs: an unplugged simulated adapter ends the session and Reconnect brings the fleet back; a fresh fleet is switched to position mode on its own; every fault statement carries the clearing instruction. The sim cannot latch a fault within an exchange, so the Clear button is covered by unit tests on the statement and visibility rules.

https://claude.ai/code/session_015YgEehU5GLftenbuhpKWMi