fix(uddf): trim mixRef + order-independent tank lookup in test

Addresses Copilot review feedback on PR #253:
- tankdata mixRef is now trimmed before being stored as
  uddfGasMixRef, so whitespace-only refs don't become
  non-resolvable identifiers downstream.
- waypoint <switchmix ref> is trimmed and skipped when empty,
  so gasSwitches entries the importer couldn't resolve to a
  tank are never emitted.
- Integration test identifies tanks by o2Percent (32% bottom /
  80% deco) instead of relying on SQLite/Drift row order,
  removing cross-version flakiness.

Author: ericgriffin

lib/core/services/export/uddf/uddf_full_import_service.dart

@@ -1372,14 +1372,13 @@ class UddfFullImportService {
       // Get linked gas mix
       final mixLink = tankDataElement.findElements('link').firstOrNull;
       if (mixLink != null) {
-        final mixRef = mixLink.getAttribute('ref');
-        if (mixRef != null) {
+        final rawMixRef = mixLink.getAttribute('ref');
+        final mixRef = rawMixRef?.trim();
+        if (mixRef != null && mixRef.isNotEmpty) {
           // Record the UDDF gas-mix UUID on the tank so the importer can
           // resolve waypoint-level <switchmix ref> markers (which reference
           // gas mixes, not tanks) back to a tank for the gas_switches row.
-          if (mixRef.isNotEmpty) {
-            tankInfo['uddfGasMixRef'] = mixRef;
-          }
+          tankInfo['uddfGasMixRef'] = mixRef;
           if (gasMixes.containsKey(mixRef)) {
             tankInfo['gasMix'] = gasMixes[mixRef];
           }
@@ -1576,8 +1575,12 @@ class UddfFullImportService {
 
         final switchMix = waypoint.findElements('switchmix').firstOrNull;
         if (switchMix != null) {
-          final mixRef = switchMix.getAttribute('ref');
-          if (mixRef != null) {
+          final rawMixRef = switchMix.getAttribute('ref');
+          final mixRef = rawMixRef?.trim();
+          // Skip emission entirely when the ref is empty or whitespace-only:
+          // the importer would have no way to resolve such a dangling ref
+          // back to a persisted tank row.
+          if (mixRef != null && mixRef.isNotEmpty) {
             // Emit a gas switch entry for the importer to persist. Shape
             // matches the top-level <gasswitches> parser (timestamp/depth/
             // tankRef), plus `gasMixRef` so the importer can resolve the

test/features/dive_import/macdive_waypoint_gas_switch_test.dart

@@ -166,22 +166,27 @@ void main() {
           reason: 'expected one gas_switches row per <switchmix ref>',
         );
 
-        // Tanks are imported in UDDF order; tank[0] = bottom gas, tank[1] = deco.
-        // Importer preserves tank order from the parsed `tanks` list.
-        final bottomTankId = diveTanks[0].id;
-        final decoTankId = diveTanks[1].id;
+        // Identify tanks by o2Percent rather than relying on row insertion
+        // order: SQLite/Drift do not guarantee `select(...).get()` ordering
+        // without an explicit ORDER BY, so positional indexing is flaky
+        // across engine versions. The synthetic UDDF uses 32% for the
+        // bottom mix and 80% for the deco mix, which are unambiguous.
+        final bottomTankId = diveTanks.firstWhere((t) => t.o2Percent == 32).id;
+        final decoTankId = diveTanks.firstWhere((t) => t.o2Percent == 80).id;
 
         final byTimestamp = {for (final gs in switches) gs.timestamp: gs};
         expect(byTimestamp.keys, containsAll(<int>[0, 2400]));
         expect(
           byTimestamp[0]!.tankId,
           bottomTankId,
-          reason: 'waypoint 0s switch to mix-bottom should land on tank[0]',
+          reason:
+              'waypoint 0s switch to mix-bottom should land on the 32% tank',
         );
         expect(
           byTimestamp[2400]!.tankId,
           decoTankId,
-          reason: 'waypoint 2400s switch to mix-deco should land on tank[1]',
+          reason:
+              'waypoint 2400s switch to mix-deco should land on the 80% tank',
         );
         expect(byTimestamp[2400]!.depth, 6.0);
       },