diff --git a/apps/api/prisma/migrations/20260709062007_page_versions/migration.sql b/apps/api/prisma/migrations/20260709062007_page_versions/migration.sql
new file mode 100644
index 0000000..0031ad5
--- /dev/null
+++ b/apps/api/prisma/migrations/20260709062007_page_versions/migration.sql
@@ -0,0 +1,32 @@
+-- CreateEnum
+CREATE TYPE "PageVersionTrigger" AS ENUM ('AUTO', 'MANUAL', 'PRE_RESTORE');
+
+-- CreateTable
+CREATE TABLE "page_versions" (
+    "id" TEXT NOT NULL,
+    "page_id" TEXT NOT NULL,
+    "ydoc_snapshot" BYTEA NOT NULL,
+    "trigger" "PageVersionTrigger" NOT NULL,
+    "label" TEXT,
+    "contributor_ids" TEXT[],
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "page_versions_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "page_pending_contributors" (
+    "page_id" TEXT NOT NULL,
+    "user_id" TEXT NOT NULL,
+
+    CONSTRAINT "page_pending_contributors_pkey" PRIMARY KEY ("page_id","user_id")
+);
+
+-- CreateIndex
+CREATE INDEX "page_versions_page_id_created_at_idx" ON "page_versions"("page_id", "created_at");
+
+-- AddForeignKey
+ALTER TABLE "page_versions" ADD CONSTRAINT "page_versions_page_id_fkey" FOREIGN KEY ("page_id") REFERENCES "pages"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "page_pending_contributors" ADD CONSTRAINT "page_pending_contributors_page_id_fkey" FOREIGN KEY ("page_id") REFERENCES "pages"("id") ON DELETE CASCADE ON UPDATE CASCADE;
diff --git a/apps/api/prisma/schema.prisma b/apps/api/prisma/schema.prisma
index d0c8ac5..f4a46d3 100644
--- a/apps/api/prisma/schema.prisma
+++ b/apps/api/prisma/schema.prisma
@@ -101,11 +101,13 @@ model Page {
   deletedAt DateTime? @map("deleted_at")
   deletedBy String?   @map("deleted_by")
 
-  pond         Pond              @relation(fields: [pondId], references: [id])
-  creator      User              @relation(fields: [createdBy], references: [id])
-  updates      PageUpdate[]
-  contentCache PageContentCache?
-  attachments  Attachment[]
+  pond                Pond                     @relation(fields: [pondId], references: [id])
+  creator             User                     @relation(fields: [createdBy], references: [id])
+  updates             PageUpdate[]
+  contentCache        PageContentCache?
+  attachments         Attachment[]
+  versions            PageVersion[]
+  pendingContributors PagePendingContributor[]
 
   @@unique([pondId, slug])
   @@index([pondId])
@@ -127,6 +129,48 @@ model PageUpdate {
   @@map("page_updates")
 }
 
+enum PageVersionTrigger {
+  AUTO
+  MANUAL
+  PRE_RESTORE
+}
+
+/// Version snapshot of a page (ADR 0013, data-model.md). `ydocSnapshot` is a
+/// full, self-contained encoded Yjs state — restore never depends on the
+/// update log, so compaction (#40) cannot lose restorable history.
+/// `contributorIds` is the set of users who edited since the previous version
+/// (derived from the live session, #41). Created automatically at session end
+/// and on an active-editing interval by collab, and on demand (named) by the
+/// api; `PRE_RESTORE` snapshots are written before a restore (#42).
+model PageVersion {
+  id             String             @id @default(uuid())
+  pageId         String             @map("page_id")
+  ydocSnapshot   Bytes              @map("ydoc_snapshot")
+  trigger        PageVersionTrigger
+  label          String?
+  contributorIds String[]           @map("contributor_ids")
+  createdAt      DateTime           @default(now()) @map("created_at")
+
+  page Page @relation(fields: [pageId], references: [id], onDelete: Cascade)
+
+  @@index([pageId, createdAt])
+  @@map("page_versions")
+}
+
+/// Accumulator of users who have edited a page since its last version (#41).
+/// Collab flushes the current session's contributors here (deduplicated by the
+/// composite key); version creation on either side reads and clears it in the
+/// same transaction as writing the snapshot. Cascades on page purge (ADR 0013).
+model PagePendingContributor {
+  pageId String @map("page_id")
+  userId String @map("user_id")
+
+  page Page @relation(fields: [pageId], references: [id], onDelete: Cascade)
+
+  @@id([pageId, userId])
+  @@map("page_pending_contributors")
+}
+
 /// Live-session registry the collab server keeps current: one row per page
 /// with an open collaboration session, refreshed by a heartbeat (issue #40).
 /// The compaction job reads it to skip pages that are being edited; a stale
diff --git a/apps/api/src/compaction/compaction.service.db.test.ts b/apps/api/src/compaction/compaction.service.db.test.ts
index fe234f8..611c4e4 100644
--- a/apps/api/src/compaction/compaction.service.db.test.ts
+++ b/apps/api/src/compaction/compaction.service.db.test.ts
@@ -85,21 +85,24 @@ describe.skipIf(!hasTestDb)('CompactionService (db, issue #40)', () => {
         pondId,
         title: 'Test',
         slug: `p-${id.slice(0, 8)}`,
-        ydocState: Buffer.from(Y.encodeStateAsUpdate(new Y.Doc())),
+        // A fresh Uint8Array copy, not a Buffer: Prisma's Bytes input type is
+        // Uint8Array<ArrayBuffer>, which a Buffer (ArrayBufferLike) does not
+        // satisfy under strict types (handoff gotcha).
+        ydocState: new Uint8Array(Y.encodeStateAsUpdate(new Y.Doc())),
         sortKey: 'a0',
         createdBy: userId,
       },
     });
     const master = new Y.Doc();
     let vector = Y.encodeStateVector(master);
-    const rows: { id: string; pageId: string; seq: number; update: Buffer }[] = [];
+    const rows: { id: string; pageId: string; seq: number; update: Uint8Array<ArrayBuffer> }[] = [];
     for (let i = 0; i < logRows; i += 1) {
       master.getText('log').insert(i, 'x');
       rows.push({
         id: randomUUID(),
         pageId: id,
         seq: i,
-        update: Buffer.from(Y.encodeStateAsUpdate(master, vector)),
+        update: new Uint8Array(Y.encodeStateAsUpdate(master, vector)),
       });
       vector = Y.encodeStateVector(master);
     }