Enable acknowledged RX retune caches for RAK3401

docs/test-results/rak3401_radio2_sf5_bw500_p384_2026-10-23.md

@@ -93,9 +93,10 @@ time. An unplugged-USB, SWD-only sleep experiment would be a separate test.
 
 Source inspection found concrete speed candidates, without changing this
 baseline: RAK currently uses the default 2 MHz byte-at-a-time SPI path,
-although a buffered nRF52 HAL exists; the retune path also performs modem
-queries during setup and maximum-airtime calculation. Their individual costs
-were not measured by this capture. Faster switching and any receiver repair
+although a buffered nRF52 HAL exists; the retune path also queries the modem
+during setup and repeats the IQ workaround. Its custom airtime override already
+uses cached parameters and does not issue a second modem query. Their individual
+costs were not measured by this capture. Faster switching and any receiver repair
 need fresh source-bound RF validation before a qualification claim.
 
 ## Controller correction and restoration