Drain received packets in single-profile radio fault backoff as well as
dual-profile mode. Share the normal channel-clear and bounded busy policy
with driver retries so a failed send cannot retry blindly or bypass the
existing single-retry limit.
Retain an unadmitted OTA request flight and count v2 fallback evidence only
after a sparse retry enters the transmit queue. Local queue congestion no
longer disables v2 before a request was sent or discards received fragments.
Include primary airtime when temporary RX-only radio2 crosses requests onto
that channel, keeping response allowances conservative on slower profiles.
Add six native regressions, including five failing-before cases, and document
the queue-admission and crossover timing behavior.
Validation: 1,502 native tests, 29 integration checks, and five firmware
builds passed across ESP32-S3, nRF52, and STM32.