diff --git a/src/lib/cycle/backup.ts b/src/lib/cycle/backup.ts
index 048e52f8c..1a216b812 100644
--- a/src/lib/cycle/backup.ts
+++ b/src/lib/cycle/backup.ts
@@ -64,6 +64,12 @@ export interface CycleBackupSection {
     isPredicted?: boolean;
     syncVersion?: number;
     deletedAt?: string | null;
+    /**
+     * Disaster recovery only: the start that folded this one in. A bare id with
+     * no foreign key, meaningful only because the same file carries the ids of
+     * the starts it names.
+     */
+    absorbedIntoId?: string | null;
     createdAt?: string;
     updatedAt?: string;
   }>;
@@ -214,6 +220,7 @@ export async function buildCycleBackupSection(
             isPredicted: c.isPredicted,
             syncVersion: c.syncVersion,
             deletedAt: c.deletedAt?.toISOString() ?? null,
+            absorbedIntoId: c.absorbedIntoId,
             createdAt: c.createdAt.toISOString(),
             updatedAt: c.updatedAt.toISOString(),
           }
@@ -432,6 +439,12 @@ export async function restoreCycleData(
   // re-attach to their owning span.
   const cycleIdByStart = new Map<string, string>();
   const restoredCycleIds = new Set<string>();
+  // A folded start names the start that absorbed it. Kept only when that start
+  // is in the same file under the same id; a pointer at nothing would stop the
+  // folded row from ever coming back, which is what the column is for.
+  const carriedCycleIds = new Set(
+    payload.cycles.flatMap((c) => (c.id ? [c.id] : [])),
+  );
   for (const c of payload.cycles) {
     const created = await tx.menstrualCycle.create({
       data: {
@@ -447,6 +460,10 @@ export async function restoreCycleData(
         isPredicted: c.isPredicted ?? false,
         syncVersion: c.syncVersion ?? 0,
         deletedAt: c.deletedAt ? new Date(c.deletedAt) : null,
+        absorbedIntoId:
+          c.absorbedIntoId && carriedCycleIds.has(c.absorbedIntoId)
+            ? c.absorbedIntoId
+            : null,
         ...(c.createdAt ? { createdAt: new Date(c.createdAt) } : {}),
         ...(c.updatedAt ? { updatedAt: new Date(c.updatedAt) } : {}),
       },
diff --git a/src/lib/export/full-backup-payload.ts b/src/lib/export/full-backup-payload.ts
index d5a9137d7..a1c9396c3 100644
--- a/src/lib/export/full-backup-payload.ts
+++ b/src/lib/export/full-backup-payload.ts
@@ -887,6 +887,9 @@ export async function buildFullBackupPayload(
     // `source` is part of the composite PK, so it has to ride along or a
     // restore cannot tell a manual water entry from a synced day total. The
     // table carries no tombstone, so both purposes read the same shape.
+    // `externalSourceVersion` is the source's own version marker, stored so
+    // the sync can replay it back unchanged; `createdAt` is when the day
+    // first arrived. Neither can be rebuilt after a restore.
     prisma.nutrientIntakeDay.findMany({
       where: { userId },
       select: {
@@ -895,6 +898,8 @@ export async function buildFullBackupPayload(
         amount: true,
         unit: true,
         source: true,
+        externalSourceVersion: true,
+        createdAt: true,
       },
       orderBy: [{ day: "desc" }, { nutrient: "asc" }],
     }),
@@ -1293,6 +1298,8 @@ export async function buildFullBackupPayload(
       amount: n.amount,
       unit: n.unit,
       source: n.source,
+      externalSourceVersion: n.externalSourceVersion,
+      createdAt: n.createdAt.toISOString(),
     })),
   };
 
diff --git a/src/lib/export/records-backup.ts b/src/lib/export/records-backup.ts
index 2bb4cd278..99e97d032 100644
--- a/src/lib/export/records-backup.ts
+++ b/src/lib/export/records-backup.ts
@@ -142,6 +142,8 @@ export interface WorkoutBackupEntry {
   externalId: string | null;
   /** Canonical DR only; portable workout summaries keep their existing shape. */
   metadata?: Prisma.JsonValue;
+  /** Canonical DR only, beside `metadata`: the source's own version marker. */
+  externalSourceVersion?: string | null;
 }
 
 export interface DocumentBackupEntry {
@@ -516,6 +518,7 @@ export async function buildRecordsBackupSection(
           createdAt: w.createdAt.toISOString(),
           updatedAt: w.updatedAt.toISOString(),
           ...(w.metadata == null ? {} : { metadata: w.metadata }),
+          externalSourceVersion: w.externalSourceVersion,
         }
       : {}),
     sportType: w.sportType,
diff --git a/src/lib/export/restore-backup.ts b/src/lib/export/restore-backup.ts
index ff3bb1175..da1e3baca 100644
--- a/src/lib/export/restore-backup.ts
+++ b/src/lib/export/restore-backup.ts
@@ -2139,6 +2139,7 @@ export async function restoreBackup(
               pauseDurationSec: workout.pauseDurationSec ?? null,
               source: workout.source as never,
               externalId: workout.externalId ?? null,
+              externalSourceVersion: workout.externalSourceVersion ?? null,
               ...(workout.metadata == null
                 ? {}
                 : { metadata: toJson(workout.metadata) }),
@@ -2161,6 +2162,8 @@ export async function restoreBackup(
               amount: n.amount,
               unit: n.unit,
               source: n.source,
+              externalSourceVersion: n.externalSourceVersion ?? null,
+              ...(n.createdAt ? { createdAt: new Date(n.createdAt) } : {}),
             })),
           });
         }
diff --git a/src/lib/validations/backup.ts b/src/lib/validations/backup.ts
index 06eb54aa7..e6412d98f 100644
--- a/src/lib/validations/backup.ts
+++ b/src/lib/validations/backup.ts
@@ -559,6 +559,7 @@ const cycleSpanSchema = z
     tz: z.string().nullable().optional(),
     syncVersion: z.number().int().optional(),
     deletedAt: isoDateTime.nullable().optional(),
+    absorbedIntoId: z.string().min(1).nullable().optional(),
     createdAt: isoDateTime.optional(),
     updatedAt: isoDateTime.optional(),
   })
@@ -691,6 +692,9 @@ const nutrientDaySchema = z
     // Closed set in app code rather than a DB enum; kept as a string here so a
     // future source does not make an old file unparseable.
     source: z.string().min(1),
+    // Absent from files written before v1.39.7.
+    externalSourceVersion: z.string().nullable().optional(),
+    createdAt: isoDateTime.optional(),
   })
   .passthrough();
 
@@ -1641,6 +1645,7 @@ const workoutBackupSchema = z
     pauseDurationSec: z.number().int().nullable().optional(),
     source: z.enum(MeasurementSource),
     externalId: z.string().nullable().optional(),
+    externalSourceVersion: z.string().nullable().optional(),
     metadata: z.json().optional(),
     createdAt: isoDateTime.optional(),
     updatedAt: isoDateTime.optional(),