startAttachedBackendMonitor's dead/drifted-backend recovery called
invalidatePrimaryConnection(), which sets primaryRecoverySuppressed
before scheduleUnexpectedPrimaryRecovery() reads it back as an
intentional teardown and refuses to claim the respawn, leaving the
desktop app with no backend. Clear the slot via
backendConnectionState.invalidate() directly instead, since an
unexpected attach teardown is exactly what the supervisor's recovery
path exists for.
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