feat(trail): auto-save GPS trail on shutdown (Trail settings toggle)

Losing the whole route on a low-battery auto-shutdown was the worst solo-mode
failure. New NodePrefs::trail_autosave_lowbatt toggle (Tools > Trail >
Settings > Auto-save, default OFF): UITask::shutdown() writes the live trail
to /trail when the toggle is on and _trail.count() > 0. The count guard stops
an empty trail from wiping a previously saved one; it overwrites the same
/trail file the manual Trail > Save uses.

Schema bumped 0xC0DE001A -> 0xC0DE001B: append-only tail field with a load
clamp, so pre-0x1B saves default to off. sizeof(NodePrefs) is unchanged (the
byte fits existing padding after keyboard_type), so the tripwire assert stays
2496.

Builds green: WioTrackerL1_companion_solo_dual (RAM 69.9%, Flash 62.8%).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/DataStore.cpp

@@ -476,6 +476,12 @@ void DataStore::loadPrefsInt(const char *filename, NodePrefs& _prefs, double& no
     if (_prefs.page_order[i] > NodePrefs::HPB_COUNT) _prefs.page_order[i] = 0;
   }
 
+  // → 0xC0DE001B: append trail_autosave_lowbatt at the tail. A pre-0x1B file has
+  // the old sentinel bytes / EOF here; rd() zero-inits when absent and the clamp
+  // below turns any stray value into 0 (off), so upgraders default to off.
+  rd(&_prefs.trail_autosave_lowbatt, sizeof(_prefs.trail_autosave_lowbatt));
+  if (_prefs.trail_autosave_lowbatt > 1) _prefs.trail_autosave_lowbatt = 0;
+
   // Schema sentinel: bumped on layout changes. Mismatch means an older file
   // (or a different schema); rd() already zero-inits any fields not present,
   // so we just log it — next savePrefs writes the current sentinel.
@@ -661,6 +667,7 @@ void DataStore::savePrefs(const NodePrefs& _prefs, double node_lat, double node_
     // appended here so the on-disk head stays the original 11 bytes.
     file.write((uint8_t *)&_prefs.page_order[NodePrefs::PAGE_ORDER_LEN_V1],
                NodePrefs::PAGE_ORDER_LEN - NodePrefs::PAGE_ORDER_LEN_V1);
+    file.write((uint8_t *)&_prefs.trail_autosave_lowbatt, sizeof(_prefs.trail_autosave_lowbatt));
 
     // Tail sentinel — must be last. See NodePrefs::SCHEMA_SENTINEL. Its write is
     // the one we check: once the flash fills, writes return 0, so a good

examples/companion_radio/NodePrefs.h

@@ -289,6 +289,12 @@ struct NodePrefs {  // persisted to file
   // (phone-keypad groups, cycled with repeated Enter presses — see KeyboardWidget.h).
   uint8_t  keyboard_type;
 
+  // Auto-save the live GPS trail to /trail on shutdown (covers the low-battery
+  // auto-shutdown, which otherwise loses the whole route). Only writes when the
+  // trail has points and the toggle is on. 0 = off (default), 1 = on.
+  // [Tools › Trail › Settings › Auto-save]
+  uint8_t  trail_autosave_lowbatt;
+
   // Single source of truth for the live-share option tables (shared by the Map
   // UI labels and the auto-send engine in UITask).
   static const uint8_t LOC_SHARE_MOVE_COUNT = 4;
@@ -351,7 +357,7 @@ struct NodePrefs {  // persisted to file
   // adding/removing/reordering fields in DataStore::savePrefs/loadPrefsInt so
   // older saves are detected on load and skipped (zero-init defaults kept).
   // High 24 bits identify the file format; low byte is the schema revision.
-  static const uint32_t SCHEMA_SENTINEL = 0xC0DE001A;
+  static const uint32_t SCHEMA_SENTINEL = 0xC0DE001B;
 
   // Bit-index for each home page. Used by page_order (entries store bit+1) and
   // by home_pages_mask. Single source of truth — both HomeScreen::pageBit/bitToPage

examples/companion_radio/ui-new/TrailScreen.h

@@ -72,7 +72,7 @@ class TrailScreen : public UIScreen {
   // (Start/Stop tracking, Reset). PopupMenu stores label pointers verbatim, so
   // the labels live in member buffers that get refreshed in openActionMenu()
   // and after every LEFT/RIGHT cycle.
-  enum ActionId { ACT_MIN_DIST, ACT_UNITS, ACT_GRID, ACT_AUTOPAUSE, ACT_MARK_AVG, ACT_TOGGLE, ACT_SAVE, ACT_LOAD, ACT_RESET, ACT_EXPORT, ACT_EXPORT_SAVED, ACT_MARK, ACT_WAYPOINTS, ACT_FILE, ACT_SETTINGS,
+  enum ActionId { ACT_MIN_DIST, ACT_UNITS, ACT_GRID, ACT_AUTOPAUSE, ACT_MARK_AVG, ACT_AUTOSAVE, ACT_TOGGLE, ACT_SAVE, ACT_LOAD, ACT_RESET, ACT_EXPORT, ACT_EXPORT_SAVED, ACT_MARK, ACT_WAYPOINTS, ACT_FILE, ACT_SETTINGS,
                  ACT_SHARE_NOW, ACT_TRACKBACK };
   // The action popup is multi-level: a short main menu, plus "Trail file…" and
   // "Settings…" submenus. _menu_level tracks which is open so input is routed
@@ -89,6 +89,7 @@ class TrailScreen : public UIScreen {
   char      _act_grid_label[16];
   char      _act_autopause_label[24];
   char      _act_mark_avg_label[24];
+  char      _act_autosave_label[24];
   char      _act_toggle_label[20];
 
   static const int SUMMARY_ITEM_COUNT = 5;
@@ -178,6 +179,7 @@ public:
           case ACT_UNITS:
           case ACT_GRID:
           case ACT_MARK_AVG:
+          case ACT_AUTOSAVE:
           case ACT_AUTOPAUSE: cycleSetting(act, 1); reopenSettingsAt(sel); return true;
           case ACT_SHARE_NOW:     shareMyLocationNow(); break;
           case ACT_TOGGLE:
@@ -327,6 +329,8 @@ private:
               "Auto-pause: %s", NodePrefs::trailAutoPauseLabel(p ? p->trail_autopause_idx : 0));
     snprintf(_act_mark_avg_label, sizeof(_act_mark_avg_label),
               "Mark avg: %s", NodePrefs::gpsAvgLabel(p ? p->gps_avg_idx : 0));
+    snprintf(_act_autosave_label, sizeof(_act_autosave_label),
+              "Auto-save: %s", (p && p->trail_autosave_lowbatt) ? "ON" : "OFF");
     snprintf(_act_toggle_label, sizeof(_act_toggle_label),
               "%s tracking",  _store->isActive() ? "Stop" : "Start");
   }
@@ -394,6 +398,7 @@ private:
     pushAction(ACT_MIN_DIST,  _act_min_dist_label);
     pushAction(ACT_AUTOPAUSE, _act_autopause_label);
     pushAction(ACT_MARK_AVG,  _act_mark_avg_label);
+    pushAction(ACT_AUTOSAVE,  _act_autosave_label);
     if (_view == V_SUMMARY) pushAction(ACT_UNITS, _act_units_label);
     if (_view == V_MAP)     pushAction(ACT_GRID,  _act_grid_label);
   }
@@ -406,6 +411,7 @@ private:
     if (act == ACT_GRID)          { _map_grid = !_map_grid;                    refreshActionLabels(); return true; }
     if (act == ACT_AUTOPAUSE && p){ cycleAutoPause(p, dir); _cfg_dirty = true; refreshActionLabels(); return true; }
     if (act == ACT_MARK_AVG  && p){ cycleMarkAvg(p, dir);   _cfg_dirty = true; refreshActionLabels(); return true; }
+    if (act == ACT_AUTOSAVE  && p){ p->trail_autosave_lowbatt = !p->trail_autosave_lowbatt; _cfg_dirty = true; refreshActionLabels(); return true; }
     return false;
   }
 

examples/companion_radio/ui-new/UITask.cpp

@@ -1927,6 +1927,19 @@ bool UITask::savePrefsIfDirty(bool& dirty) {
 void UITask::shutdown(bool restart){
   the_mesh.saveRTCTime();
 
+  // Auto-save the live GPS trail before power-off when the user enabled it
+  // (Tools › Trail › Settings › Auto-save). This covers the low-battery
+  // auto-shutdown, which otherwise loses the whole route. Overwrites /trail
+  // (same file as the manual Trail › Save); guarded on count()>0 so an empty
+  // trail can't wipe a previously saved one.
+  if (_node_prefs && _node_prefs->trail_autosave_lowbatt && _trail.count() > 0) {
+    DataStore* ds = the_mesh.getDataStore();
+    if (ds) {
+      File f = ds->openWrite("/trail");
+      if (f) { _trail.writeTo(f); f.close(); }
+    }
+  }
+
   #ifdef PIN_BUZZER
   /* note: we have a choice here -
      we can do a blocking buzzer.loop() with non-deterministic consequences