Preserve OTA block progress and channel checks during radio recovery

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.

docs/ota_user_guide.md

@@ -422,6 +422,10 @@ maintenance rate even when LoRa pacing is slow.
 If the local transmit queue cannot accept a catalog, manifest, or leaf request,
 OTA keeps it pending without consuming a network retry. Successfully queued
 requests that receive no answer still have bounded retries.
+Blocked block requests also preserve the v2 transfer format and fragments
+already received; queue congestion alone does not trigger legacy fallback.
+Retry timing includes the primary channel when an RX-only temporary radio2
+uses crossover to send requests there.
 
 `ota config speed 0.5` is an equivalent setter. `ota config speed` and
 `ota speed` read the current factor; the `ota config` summary also includes it.