Fix VO2 max sync: robust fallback when maxmet range returns non-list or valueless entries

The previous code used `if not mm_history:` to decide whether to fall back to
get_training_status(). If the maxmet API returned a non-empty list with no valid
vo2max values (or a non-list type), the fallback was skipped and nothing stored.

Changes:
- Normalise mm_raw: only use it if it's a list (handles dict/None responses)
- Check valid_from_range: fall back to training_status whenever no usable value
  was found in the range query, regardless of whether it returned entries
- Upgrade all related log lines to INFO so the result is visible without debug mode
- Guard the entry loop against non-dict items

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/services/garmin_connect_sync.py

@@ -332,25 +332,40 @@ def sync_wellness(garmin, user_id: int, since: Optional[datetime], db,
     if fa_data:
         fa_age = fa_data.get("fitnessAge") or fa_data.get("achievableFitnessAge")
 
+    mm_entries = []
     try:
-        mm_history = garmin.connectapi(
+        mm_raw = garmin.connectapi(
             f"/metrics-service/metrics/maxmet/daily/{start_date.isoformat()}/{today_str}"
         )
+        logger.info("maxmet range query returned type=%s len=%s",
+                    type(mm_raw).__name__,
+                    len(mm_raw) if isinstance(mm_raw, (list, dict)) else "n/a")
+        if isinstance(mm_raw, list):
+            mm_entries = mm_raw
     except Exception as exc:
-        logger.debug("maxmet history fetch failed: %s", exc)
-        mm_history = []
+        logger.info("maxmet history fetch failed: %s", exc)
 
-    # Fall back to most-recent from training status if history is empty
-    if not mm_history:
+    # Check whether the range query yielded any usable vo2max values
+    valid_from_range = any(
+        (entry.get("vo2MaxPreciseValue") or entry.get("vo2MaxValue") or 0)
+        for entry in mm_entries
+        if isinstance(entry, dict)
+    )
+
+    # Always fall back to training_status when the range query had no valid data
+    if not valid_from_range:
         ts_data = _safe(garmin.get_training_status, today_str)
-        generic = (ts_data or {}).get("mostRecentVO2Max", {}).get("generic") or {}
+        generic = ((ts_data or {}).get("mostRecentVO2Max") or {}).get("generic") or {}
         v = generic.get("vo2MaxPreciseValue") or generic.get("vo2MaxValue")
+        logger.info("training_status vo2max=%s at %s", v, generic.get("calendarDate"))
         if v and float(v) > 0:
-            mm_history = [{"calendarDate": generic.get("calendarDate") or today_str,
+            mm_entries = [{"calendarDate": generic.get("calendarDate") or today_str,
                            "vo2MaxPreciseValue": float(v)}]
 
     stored = 0
-    for entry in (mm_history or []):
+    for entry in mm_entries:
+        if not isinstance(entry, dict):
+            continue
         v = entry.get("vo2MaxPreciseValue") or entry.get("vo2MaxValue")
         if not v or float(v) <= 0:
             continue
@@ -372,8 +387,7 @@ def sync_wellness(garmin, user_id: int, since: Optional[datetime], db,
             logger.warning("Failed to upsert VO2 max for %s: %s", entry_date, exc)
             db.rollback()
 
-    if stored:
-        logger.info("Stored %d VO2 max data points", stored)
+    logger.info("VO2 max: stored=%d from range_valid=%s", stored, valid_from_range)
 
     return processed