fix(import): cut lab CSV duplicate days in the zone the file is read in

The rows were parsed in the query's timezone while the duplicate keys
used the account's, so two draws on separate days of the file's zone
could collapse into one, or one day split in two.

src/lib/import/labs-csv.ts

@@ -275,6 +275,10 @@ export async function importLabsCsv(args: {
 }): Promise<RecordImportResult> {
   const { userId, tz, query } = args;
   const dryRun = query.dryRun;
+  // One zone for everything: the file's times are read in it, and the
+  // calendar day a reading is a duplicate on is cut in it too. Cutting the
+  // days in the account's zone while reading the file in another split one
+  // draw day in two, or folded two into one.
   const timezone = query.timezone ?? tz;
   const report = new RecordImportReport("labs", dryRun);
   const index: MarkerIndex = await loadMarkerIndex(prisma, userId);
@@ -365,7 +369,9 @@ export async function importLabsCsv(args: {
     }
 
     // 2. Duplicates against the record, one query for the chunk.
-    const days = planned.map((p) => labReadingDay(p.row.takenAt, tz)).sort();
+    const days = planned
+      .map((p) => labReadingDay(p.row.takenAt, timezone))
+      .sort();
     const existingKeys = new Set<string>();
     if (planned.length > 0) {
       const from = labReadingDaySearchRange(days[0]).gte;
@@ -396,10 +402,10 @@ export async function importLabsCsv(args: {
         },
       });
       for (const e of existing) {
-        for (const k of readingKeys(e, tz)) existingKeys.add(k);
+        for (const k of readingKeys(e, timezone)) existingKeys.add(k);
         // A reading filed under a marker also answers to its printed name.
         if (e.biomarkerId) {
-          for (const k of readingKeys({ ...e, biomarkerId: null }, tz))
+          for (const k of readingKeys({ ...e, biomarkerId: null }, timezone))
             existingKeys.add(k);
         }
       }
@@ -418,10 +424,10 @@ export async function importLabsCsv(args: {
         sourceUnit: row.unit,
       };
       const keys = [
-        ...readingKeys(probe, tz),
-        ...readingKeys({ ...probe, biomarkerId: null }, tz),
+        ...readingKeys(probe, timezone),
+        ...readingKeys({ ...probe, biomarkerId: null }, timezone),
         ...(marker
-          ? readingKeys({ ...probe, biomarkerId: marker.id }, tz)
+          ? readingKeys({ ...probe, biomarkerId: marker.id }, timezone)
           : []),
       ];
       if (keys.some((k) => existingKeys.has(k) || seen.has(k))) {
@@ -506,7 +512,7 @@ export async function importLabsCsv(args: {
       });
       for (const k of [
         ...keys,
-        ...readingKeys({ ...probe, biomarkerId: biomarker.id }, tz),
+        ...readingKeys({ ...probe, biomarkerId: biomarker.id }, timezone),
       ])
         seen.add(k);
       report.valid += 1;