feat: PROVES USP radio integration (collapses PRs #1-#2)

subsys/usb/device_next/class/usbd_cdc_acm.c

@@ -383,6 +383,10 @@ static void usbd_cdc_acm_disable(struct usbd_class_data *const c_data)
 
 	atomic_clear_bit(&data->state, CDC_ACM_CLASS_ENABLED);
 	atomic_clear_bit(&data->state, CDC_ACM_CLASS_SUSPENDED);
+	/* Clear TX_FIFO_BUSY on disable so a stuck IN transfer does not block
+	 * the TX path after the host reconnects and re-enables the class.
+	 */
+	atomic_clear_bit(&data->state, CDC_ACM_TX_FIFO_BUSY);
 	LOG_INF("Configuration disabled");
 }
 
@@ -653,6 +657,13 @@ static void cdc_acm_tx_fifo_handler(struct k_work *work)
 
 	if (atomic_test_and_set_bit(&data->state, CDC_ACM_TX_FIFO_BUSY)) {
 		LOG_DBG("TX transfer already in progress");
+		/* Reschedule if data is waiting - guards against a stuck IN transfer
+		 * where the host stops issuing IN tokens (e.g. macOS flow-control).
+		 * The retry is a no-op once the completion fires and clears BUSY.
+		 */
+		if (!ring_buf_is_empty(data->tx_fifo.rb)) {
+			cdc_acm_work_schedule(&data->tx_fifo_work, K_MSEC(10));
+		}
 		return;
 	}
 
@@ -998,6 +1009,7 @@ static void cdc_acm_poll_out(const struct device *dev, const unsigned char c)
 	struct cdc_acm_uart_data *const data = dev->data;
 	k_spinlock_key_t key;
 	uint32_t wrote;
+	int retries = 20;
 
 	while (true) {
 		key = k_spin_lock(&data->lock);
@@ -1008,7 +1020,15 @@ static void cdc_acm_poll_out(const struct device *dev, const unsigned char c)
 			break;
 		}
 
-		if (k_is_in_isr() || !data->flow_ctrl) {
+		/* Bounded wait: with an attached-but-stalled host session (macOS
+		 * ceases IN polling for minutes at a time), an unbounded sleep-retry
+		 * here makes every console write take the full stall duration. Any
+		 * thread that logs (event text loggers, assert reporting) then backs
+		 * up its own queues and cascades into a system-wide com livelock.
+		 * After ~20 ms of backpressure, treat the console as best-effort and
+		 * discard, exactly like the detached (!flow_ctrl) case below.
+		 */
+		if (k_is_in_isr() || !data->flow_ctrl || retries-- <= 0) {
 			LOG_WRN_ONCE("Ring buffer full, discard data");
 			break;
 		}