refactor(measurements): drop the write-only aggregation columns (migration 0272)

Migration 0263 added three columns beside the Apple Health `stats:*`
authority ladder. Only `aggregation_provenance` is ever read back: the
external-measurement reconciler selects it and refuses a lower-authority write
against a higher-authority canonical row, and the cumulative drain reads it
too. That column stays.

`aggregation_contributor_count` and `aggregation_selected_source_hash` are
written by three call sites and read by none. No select, no raw SQL, no export,
no backup, no API contract, no repair path. The import-time selection keeps its
deterministic tiebreak, which compares an in-memory map key computed per flush
rather than a value read back from the table.

Both are plain nullable scalars with no index, unique, check or foreign key, so
the drop is a catalog-only operation that touches no measured value.

src/app/api/measurements/batch/route.ts

@@ -544,8 +544,6 @@ async function postBatch(request: NextRequest): Promise<Response> {
               .rhythmClassification as Prisma.MeasurementUncheckedCreateInput["rhythmClassification"],
             deviceType: p.row.deviceType as string | null,
             aggregationProvenance: statsRow ? "HEALTHKIT_STATISTICS" : null,
-            aggregationContributorCount: null,
-            aggregationSelectedSourceHash: null,
           },
           { exactExternalMatch: statsRow ? "update" : "duplicate" },
         ),

src/lib/measurements/__tests__/import-apple-health-export.test.ts

@@ -652,11 +652,7 @@ describe("streamParseExportXml — cumulative source-day estimates", () => {
     expect(prisma._measurements[0]).toMatchObject({
       value: 8_526,
       aggregationProvenance: "EXPORT_XML_SOURCE_MAX",
-      aggregationContributorCount: 2,
     });
-    expect(prisma._measurements[0]?.aggregationSelectedSourceHash).toMatch(
-      /^[a-f0-9]{64}$/,
-    );
     expect(result.cumulativeEstimates).toEqual({ days: 1, rows: 1 });
   });
 
@@ -675,7 +671,6 @@ describe("streamParseExportXml — cumulative source-day estimates", () => {
         type: mapping.measurementType,
         value: 30,
         aggregationProvenance: "EXPORT_XML_SOURCE_MAX",
-        aggregationContributorCount: 2,
       });
     },
   );
@@ -694,7 +689,6 @@ describe("streamParseExportXml — cumulative source-day estimates", () => {
       expect(prisma._measurements[0]).toMatchObject({
         type: mapping.measurementType,
         value: 50,
-        aggregationContributorCount: 1,
       });
     },
   );
@@ -712,7 +706,6 @@ describe("streamParseExportXml — cumulative source-day estimates", () => {
     expect(prisma._measurements).toHaveLength(1);
     expect(prisma._measurements[0]).toMatchObject({
       value: 100,
-      aggregationContributorCount: 1,
     });
   });
 
@@ -1171,7 +1164,6 @@ describe("streamParseExportXml — memory ceiling", () => {
     expect(prisma._measurements).toHaveLength(1);
     expect(prisma._measurements[0]).toMatchObject({
       value: 10_000,
-      aggregationContributorCount: 1,
     });
 
     // Heap delta should be modest — we tolerate a generous 100 MB so a

src/lib/measurements/__tests__/reconcile-external-measurement.test.ts

@@ -40,8 +40,6 @@ function row(overrides: Record<string, unknown> = {}): Record<string, unknown> {
     externalId: "sleep:new",
     externalSourceVersion: null,
     aggregationProvenance: null,
-    aggregationContributorCount: null,
-    aggregationSelectedSourceHash: null,
     glucoseContext: null,
     sleepStage: "DEEP",
     rhythmClassification: null,
@@ -224,8 +222,6 @@ describe("reconcileExternalMeasurement", () => {
       sleepStage: null,
       externalId: "stats:HKQuantityTypeIdentifierStepCount:2026-07-20",
       aggregationProvenance: "HEALTHKIT_STATISTICS",
-      aggregationContributorCount: null,
-      aggregationSelectedSourceHash: null,
     });
     const { tx, measurement } = transaction([native]);
 
@@ -240,8 +236,6 @@ describe("reconcileExternalMeasurement", () => {
         sleepStage: null,
         externalId: "stats:HKQuantityTypeIdentifierStepCount:2026-07-20",
         aggregationProvenance: "EXPORT_XML_SOURCE_MAX",
-        aggregationContributorCount: 2,
-        aggregationSelectedSourceHash: "source-hash",
       }),
       { exactExternalMatch: "update" },
     );
@@ -350,8 +344,6 @@ describe("reconcileExternalMeasurement", () => {
         sleepStage: null,
         externalId: "stats:HKQuantityTypeIdentifierStepCount:2026-07-20",
         aggregationProvenance: "HEALTHKIT_STATISTICS",
-        aggregationContributorCount: null,
-        aggregationSelectedSourceHash: null,
       }),
       { exactExternalMatch: "update" },
     );
@@ -366,8 +358,6 @@ describe("reconcileExternalMeasurement", () => {
         data: expect.objectContaining({
           value: 8_600,
           aggregationProvenance: "HEALTHKIT_STATISTICS",
-          aggregationContributorCount: null,
-          aggregationSelectedSourceHash: null,
           syncVersion: { increment: 1 },
         }),
       }),

src/lib/measurements/drain-per-sample-cumulative.ts

@@ -352,8 +352,6 @@ export async function drainPerSampleCumulative(
                   externalId,
                   deletedAt: null,
                   aggregationProvenance: "LEGACY_UNKNOWN",
-                  aggregationContributorCount: null,
-                  aggregationSelectedSourceHash: null,
                   syncVersion: { increment: 1 },
                   ...(slotIsFreeForTarget
                     ? { measuredAt: canonicalTimestamp }

src/lib/measurements/import-apple-health-export.ts

@@ -680,7 +680,10 @@ export async function streamParseExportXml(
           }
         }
         if (!selected) continue;
-        const [selectedSourceHash, selectedSubtotal] = selected;
+        // Only the subtotal is carried forward. The source hash stays an
+        // in-memory map key — it is what makes the max-subtotal selection
+        // above deterministic on a tie, and it is not persisted.
+        const [, selectedSubtotal] = selected;
         if (validateMeasurementRange(type, selectedSubtotal) !== null) {
           unknown[`${type}::aggregate_out_of_range`] =
             (unknown[`${type}::aggregate_out_of_range`] ?? 0) + 1;
@@ -704,8 +707,6 @@ export async function streamParseExportXml(
               sleepStage: null,
               deviceType: null,
               aggregationProvenance: "EXPORT_XML_SOURCE_MAX",
-              aggregationContributorCount: bySource.size,
-              aggregationSelectedSourceHash: selectedSourceHash,
             },
             { exactExternalMatch: "update" },
           ),