Two UX issues when the selected relay is unreachable (e.g. user
switched from WiFi to LTE and the LAN relay is gone):
1. Pressing Register blocked the UI for ~30s while the QUIC
connect timed out against a dead host. No way to abort.
2. No feedback that the relay was unreachable — just a long
wait followed by a cryptic error.
Fix:
**Pre-flight ping**: before attempting the full register flow,
run `ping_relay` (existing Tauri command, 3s QUIC handshake
timeout). If it fails, immediately show "Server unavailable:
<error>" and re-enable the Register button. No blocking, no
wasted time. If it succeeds, proceed to register_signal.
**Cancel button**: during the register_signal await, the
Register button becomes "Cancel". Tapping it calls `deregister`
which closes the in-flight transport and makes the connect
fail immediately, breaking the await. The button goes back to
"Register on Relay" with a "Registration cancelled" message.
Flow:
[Register] → "Checking..." (disabled, 3s ping) →
ping fails → "Server unavailable" (re-enabled)
ping ok → "Cancel" (enabled, register in flight) →
user taps Cancel → "Registration cancelled" (re-enabled)
register succeeds → registered panel shown
register fails → error shown (re-enabled)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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