fix(box3): keep link alive during SD ops

No STATE frame flows while the looper is inside its blocking SD
code, so liveness relies on progress events alone — and mounting
the card before the first one can outlast the 500 ms timeout,
flashing the disconnected banner mid-save.

The timeout widens to 8 s between sending an SD command and its
terminal event, then returns to 500 ms. Also reset the progress
bar when starting an operation.

box3_display/main/link_task.c

@@ -35,6 +35,12 @@ static SemaphoreHandle_t tx_mutex;
  * (a 64-bit value would be read in two words) */
 static volatile uint32_t last_frame_ms = 0;
 static volatile bool ever_received = false;
+static volatile bool sd_pending = false;
+
+void link_set_sd_pending(bool pending)
+{
+    sd_pending = pending;
+}
 
 bool link_connected(void)
 {
@@ -44,8 +50,11 @@ bool link_connected(void)
          * instead of a false "connected" during the first 500 ms */
         return false;
     }
+    /* mounting the card and writing a chunk can both outlast the normal
+     * timeout, and no STATE frame flows during an SD operation */
+    uint32_t timeout = sd_pending ? LINK_SD_TIMEOUT_MS : LINK_TIMEOUT_MS;
     uint32_t now_ms = (uint32_t)(esp_timer_get_time() / 1000);
-    return (uint32_t)(now_ms - last_frame_ms) < LINK_TIMEOUT_MS;
+    return (uint32_t)(now_ms - last_frame_ms) < timeout;
 }
 
 void link_send_cmd(uint8_t op, uint8_t arg0, uint16_t arg1)

box3_display/main/link_task.h

@@ -30,8 +30,14 @@ extern QueueHandle_t link_state_queue;
 /* queue of link_evt_t */
 extern QueueHandle_t link_evt_queue;
 
+/* while an SD operation is in flight the looper sends no STATE frames
+ * (its core 0 task is inside the blocking SD code) and the gaps between
+ * progress events can exceed the normal liveness timeout */
+#define LINK_SD_TIMEOUT_MS 8000
+
 void link_task_start(void);
 void link_send_cmd(uint8_t op, uint8_t arg0, uint16_t arg1);
 bool link_connected(void);
+void link_set_sd_pending(bool pending);
 
 #endif /* LINK_TASK_H_ */

box3_display/main/ui.c

@@ -122,6 +122,8 @@ static void sd_save_event_cb(lv_event_t *e)
 {
     (void)e;
     lv_label_set_text(sd_status_label, "Sauvegarde...");
+    lv_bar_set_value(sd_progress, 0, LV_ANIM_OFF);
+    link_set_sd_pending(true);
     link_send_cmd(LINK_CMD_SD_SAVE,
                   (uint8_t)lv_dropdown_get_selected(sd_dropdown), 0);
 }
@@ -130,6 +132,8 @@ static void sd_load_event_cb(lv_event_t *e)
 {
     (void)e;
     lv_label_set_text(sd_status_label, "Chargement...");
+    lv_bar_set_value(sd_progress, 0, LV_ANIM_OFF);
+    link_set_sd_pending(true);
     link_send_cmd(LINK_CMD_SD_LOAD,
                   (uint8_t)lv_dropdown_get_selected(sd_dropdown), 0);
 }
@@ -493,11 +497,13 @@ void ui_apply_evt(const link_evt_t *e)
         lv_bar_set_value(sd_progress, e->arg, LV_ANIM_OFF);
         break;
     case LINK_EVT_SD_DONE:
+        link_set_sd_pending(false);
         lv_bar_set_value(sd_progress, 100, LV_ANIM_OFF);
         lv_label_set_text_fmt(sd_status_label, "Session %u OK",
                               (unsigned)e->arg);
         break;
     case LINK_EVT_SD_ERROR:
+        link_set_sd_pending(false);
         lv_label_set_text_fmt(sd_status_label, "Erreur SD (code %u)",
                               (unsigned)e->arg);
         break;