I (...) ch12_network: COURSE_BOOT chapter=12 target=esp32 mac=xx:xx:xx:xx:xx:xx
W (...) ch12_network: GPIO2 is an optional status output; UART0 log is the acceptance signal
I (...) ch12_network: COURSE_SCAN_BEGIN sequence=1 limit=16
I (...) ch12_network: COURSE_AP index=0 ssid="..." rssi=-.. channel=.. auth=...
I (...) ch12_network: COURSE_SCAN_DONE sequence=1 total=.. reported=..

允许附近没有 AP，此时 total=0、reported=0 仍是一次成功扫描。验收必须同时看到
COURSE_SCAN_BEGIN 和 COURSE_SCAN_DONE；只看到 COURSE_BOOT 不代表扫描完成。
