diff --git a/src/__tests__/collab/rowSyncProjection.test.ts b/src/__tests__/collab/rowSyncProjection.test.ts
new file mode 100644
index 000000000..fc2fba5bd
--- /dev/null
+++ b/src/__tests__/collab/rowSyncProjection.test.ts
@@ -0,0 +1,90 @@
+import { afterEach, expect, it } from 'bun:test'
+import { waitFor } from '@testing-library/react'
+import * as Y from 'yjs'
+import { Awareness } from 'y-protocols/awareness'
+import '@modules/base'
+import { seedPageDoc, seedSiteDoc, MAIN_SITE_DOC_ID, encodeCollabDocId } from '@core/collab'
+import { MAIN_BRANCH_ID } from '@core/branches'
+import type { CollabProvider, BoundCollabDoc } from '@site/collab/collabProvider'
+import { connectCollabProvider, disconnectCollabProvider } from '@site/store/slices/site/collabBinding'
+import { useEditorStore } from '@site/store/store'
+import { makePage, makeSite } from '../fixtures'
+
+function makeProvider(site: ReturnType<typeof makeSite>) {
+  const presence = new Y.Doc()
+  const awareness = new Awareness(presence)
+  const entries = new Map<string, BoundCollabDoc>()
+  const releases = new Map<string, () => void>()
+  const provider: CollabProvider = {
+    bind(id) {
+      const known = entries.get(id)
+      if (known) return known
+      const doc = new Y.Doc()
+      if (id === MAIN_SITE_DOC_ID) seedSiteDoc(doc, site)
+      else {
+        const page = site.pages.find((p) => pageId(p.id) === id)
+        if (page) seedPageDoc(doc, page)
+      }
+      let release = () => {}
+      const whenSynced = new Promise<void>((resolve) => { release = resolve })
+      const entry = { doc, synced: false, whenSynced }
+      entries.set(id, entry)
+      releases.set(id, () => { entry.synced = true; release() })
+      return entry
+    },
+    unbind(id) { entries.get(id)?.doc.destroy(); entries.delete(id) },
+    awareness,
+    status: () => 'connected',
+    canSend: () => true,
+    reconnectNow() {},
+    onStatus: () => () => {},
+    onReset: () => () => {},
+    destroy() {
+      for (const entry of entries.values()) entry.doc.destroy()
+      awareness.destroy()
+      presence.destroy()
+    },
+  }
+  return { provider, release: (id: string) => releases.get(id)?.() }
+}
+
+function pageId(id: string) {
+  return encodeCollabDocId({ kind: 'page', branchId: MAIN_BRANCH_ID, rowId: id })
+}
+
+afterEach(() => {
+  disconnectCollabProvider()
+  useEditorStore.getState().clearSite()
+})
+
+it('syncs existing pages without replacing the already projected shell', async () => {
+  const site = makeSite({ pages: [makePage(), makePage({ id: 'page-2', slug: 'second' })] })
+  useEditorStore.setState({ site })
+  const { provider, release } = makeProvider(site)
+  connectCollabProvider(provider)
+  release(MAIN_SITE_DOC_ID)
+  await waitFor(() => expect(useEditorStore.getState().site!.settings).not.toBe(site.settings))
+  const shell = useEditorStore.getState().site!.settings
+  const initial = useEditorStore.getState().site!.pages[0]
+  release(pageId('page-1'))
+  await waitFor(() => expect(useEditorStore.getState().site!.pages[0]).not.toBe(initial))
+  expect(useEditorStore.getState().site!.settings).toBe(shell)
+  const second = useEditorStore.getState().site!.pages[1]
+  release(pageId('page-2'))
+  await waitFor(() => expect(useEditorStore.getState().site!.pages[1]).not.toBe(second))
+  expect(useEditorStore.getState().site!.settings).toBe(shell)
+})
+
+it('assembles a newly discovered peer page in roster order after its doc syncs', async () => {
+  const first = makePage()
+  const peer = makePage({ id: 'peer-page', slug: 'peer' })
+  const initialSite = makeSite({ pages: [first] })
+  useEditorStore.setState({ site: initialSite })
+  const { provider, release } = makeProvider(makeSite({ pages: [peer, first] }))
+  connectCollabProvider(provider)
+  release(MAIN_SITE_DOC_ID)
+  await waitFor(() => expect(useEditorStore.getState().site!.settings).not.toBe(initialSite.settings))
+  expect(useEditorStore.getState().site!.pages.map((p) => p.id)).toEqual([first.id])
+  release(pageId(peer.id))
+  await waitFor(() => expect(useEditorStore.getState().site!.pages.map((p) => p.id)).toEqual([peer.id, first.id]))
+})
diff --git a/src/admin/pages/site/store/slices/site/collabBinding.ts b/src/admin/pages/site/store/slices/site/collabBinding.ts
index 7aadd3a81..af17371f0 100644
--- a/src/admin/pages/site/store/slices/site/collabBinding.ts
+++ b/src/admin/pages/site/store/slices/site/collabBinding.ts
@@ -58,7 +58,7 @@ import {
   treeMap,
   type CollabDocSet,
 } from '@core/collab'
-import { allDocIdsForSite, collabBranchId, notifyCollabBranchGone } from './collabBranch'
+import { allDocIdsForSite, collabBranchId, needsSiteRosterAssembly, notifyCollabBranchGone } from './collabBranch'
 import { clonePackageJson } from '@core/site-dependencies/manifest'
 import { cloneSiteRuntimeConfig } from '@core/site-runtime'
 import { validateSite } from '@core/persistence/validate'
@@ -620,10 +620,9 @@ function bindDocThroughProvider(docId: string): void {
   void binding.whenSynced.then(() => {
     gate.synced = true
     scheduleProjection(docId)
-    // A row doc bound on demand (a peer created the row) re-assembles the
-    // site once its content arrives — the roster projection skipped it
-    // while it was empty.
-    if (!isSiteDocId(docId)) scheduleProjection(siteDocId(collabBranchId()))
+    if (needsSiteRosterAssembly(storeApi?.getState().site, docId)) {
+      scheduleProjection(siteDocId(collabBranchId()))
+    }
   })
 }
 
diff --git a/src/admin/pages/site/store/slices/site/collabBranch.ts b/src/admin/pages/site/store/slices/site/collabBranch.ts
index 538eaebc3..4507afe62 100644
--- a/src/admin/pages/site/store/slices/site/collabBranch.ts
+++ b/src/admin/pages/site/store/slices/site/collabBranch.ts
@@ -7,7 +7,7 @@
  * loads; detached-mode tests run on main.
  */
 import { MAIN_BRANCH_ID } from '@core/branches'
-import { encodeCollabDocId, siteDocId } from '@core/collab'
+import { encodeCollabDocId, parseCollabDocId, siteDocId } from '@core/collab'
 import type { SiteDocument } from '@core/page-tree'
 
 let activeBranchId: string = MAIN_BRANCH_ID
@@ -45,3 +45,15 @@ export function allDocIdsForSite(site: SiteDocument): string[] {
     ...site.layouts.map((l) => encodeCollabDocId({ kind: 'layout', branchId, rowId: l.id })),
   ]
 }
+
+/**
+ * A new peer row needs roster assembly; an existing row projects independently.
+ * Revalidating the whole shell for every sync scales with rows × shell size.
+ */
+export function needsSiteRosterAssembly(site: SiteDocument | null | undefined, docId: string): boolean {
+  const parsed = parseCollabDocId(docId)
+  if (!parsed || parsed.kind === 'site' || !site) return false
+  const rows = parsed.kind === 'page' ? site.pages
+    : parsed.kind === 'component' ? site.visualComponents : site.layouts
+  return !rows.some((row) => row.id === parsed.rowId)
+}