fix: GPS never from seed — only from real check-ins

GPS (latitude/longitude) and photo_path are now NEVER set by seed
import pipelines, even if empty. GPS comes only from field tech
check-ins via the main app.

- db_writer.py: FIELDS_NEVER_FROM_SEED set, GPS always None in
  _extract_row_values, skipped in update mode
- sync.py: latitude/longitude set to None in asset_data
- FIELD_MAP.md: updated policy table

db_writer.py

@@ -156,6 +156,10 @@ EXTRA_COLUMNS = ["created_at", "updated_at"]
 EXTERNAL_PRESERVE_FIELDS = {"latitude", "longitude", "photo_path"}
 
 
+# Fields that are NEVER set from seed data — GPS comes only from real check-ins
+FIELDS_NEVER_FROM_SEED = {"latitude", "longitude", "photo_path"}
+
+
 def _serialize_value(val):
     """Convert a Python value to a SQLite-friendly value."""
     if val is None:
@@ -291,7 +295,8 @@ class DatabaseWriter:
             elif col in ("yearly_sales", "monthly_sales", "weekly_sales"):
                 row[col] = _serialize_value(machine.get(col))
             elif col in ("latitude", "longitude"):
-                row[col] = _serialize_value(machine.get(col))
+                # GPS comes only from real check-ins, never from seed
+                row[col] = None
             else:
                 val = machine.get(col)
                 if val is not None and not isinstance(val, (str, int, float, bool)):
@@ -418,6 +423,10 @@ class DatabaseWriter:
                 for col in update_cols:
                     if col == "machine_id":
                         continue  # PK — never update
+                    # GPS and photo come only from real check-ins, never from seed
+                    if col in FIELDS_NEVER_FROM_SEED:
+                        skipped_count += 1
+                        continue
                     new_val = row.get(col)
                     old_val = existing_dict.get(col)
                     # Skip if existing value is non-null/empty (MSFS or user data wins)

sync.py

@@ -200,8 +200,8 @@ def push(source_db: str, target_db: str, dry_run: bool = False) -> dict:
                 "customer_id": customer_id,
                 "location_id": location_id,
                 "assigned_to": None,
-                "latitude": _val(r, "latitude"),
+                "latitude": None,    # GPS comes only from real check-ins
-                "longitude": _val(r, "longitude"),
+                "longitude": None,   # GPS comes only from real check-ins
                 "geofence_radius_meters": 50,
                 "disney_park": _val(r, "disney_park"),
                 "is_disney": is_disney,