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The ESP8266 software serial GPIO ISR decodes a full byte into the RX buffer, then returns. With the 2026.5.0 loop cadence change the byte may sit unread for up to one loop_interval_ tick (~16 ms), which breaks timing-sensitive components (e.g. fingerprint_grow) that poll read() in a tight setup() loop and time out before bytes appear. Call wake_loop_isrsafe() from the ISR after the byte is buffered, mirroring the ESP-IDF UART path (and the same pattern ratgdo uses via SoftwareSerial::onReceive). The wake call is a single inline flag set plus esp_schedule(); IRAM-safe and essentially free. Gated on USE_UART_WAKE_LOOP_ON_RX, now enabled by default for ESP8266 (in addition to ESP32) when networking is configured.
