diff --git a/src/app/collab/yjs-sync.ts b/src/app/collab/yjs-sync.ts
index 83f022fe7..c1963d90e 100644
--- a/src/app/collab/yjs-sync.ts
+++ b/src/app/collab/yjs-sync.ts
@@ -123,6 +123,8 @@ export function createYjsGraphSync({
   getYimages,
   setSuppressYjsEvents
 }: YjsGraphSyncOptions) {
+  let pendingPageSwitch: { store: EditorStore; pageId: string } | undefined
+
   function syncNodeToYjs(nodeId: string) {
     const store = getStore()
     const ydoc = getYdoc()
@@ -250,7 +252,19 @@ export function createYjsGraphSync({
     const pages = store.graph.getPages()
     if (pages.some((page) => page.id === store.state.currentPageId)) return
     if (pages.length === 0) return
-    void store.switchPage(pages[0].id)
+    const pageId = pages[0].id
+    if (pendingPageSwitch?.store === store && pendingPageSwitch.pageId === pageId) return
+    const pending = { store, pageId }
+    pendingPageSwitch = pending
+    void store
+      .switchPage(pageId)
+      .catch((error: unknown) => {
+        if (error instanceof Error && error.name === 'AbortError') return
+        logCollabSyncError('Failed to switch to a synced page', error)
+      })
+      .finally(() => {
+        if (pendingPageSwitch === pending) pendingPageSwitch = undefined
+      })
   }
 
   return { syncNodeToYjs, syncAllNodesToYjs, applyYjsToGraph }
diff --git a/tests/engine/app/integrations/pi-mcp.test.ts b/tests/engine/app/integrations/pi-mcp.test.ts
index 61eecce3c..0840496f1 100644
--- a/tests/engine/app/integrations/pi-mcp.test.ts
+++ b/tests/engine/app/integrations/pi-mcp.test.ts
@@ -1,11 +1,12 @@
-import { describe, expect, test } from 'bun:test'
+import { afterEach, beforeEach, describe, expect, test } from 'bun:test'
 
 import { replaceMCPConnectionSettings, setMCPConnectionCredential } from '@/app/integrations/mcp'
 import { buildPiMCPServers } from '@/app/integrations/mcp/pi'
 
-import { installTauriMockWindow } from '#tests/helpers/tauri/mocks'
+import { clearTauriMocks, installTauriMockWindow } from '#tests/helpers/tauri/mocks'
 
-installTauriMockWindow()
+beforeEach(installTauriMockWindow)
+afterEach(clearTauriMocks)
 
 describe('Pi MCP configuration', () => {
   test('adapts the built-in and external MCP servers to Pi native configuration', async () => {
diff --git a/tests/engine/collab/yjs-sync.test.ts b/tests/engine/collab/yjs-sync.test.ts
index 4e6e7d345..2b8dfa371 100644
--- a/tests/engine/collab/yjs-sync.test.ts
+++ b/tests/engine/collab/yjs-sync.test.ts
@@ -1,4 +1,4 @@
-import { describe, test, expect } from 'bun:test'
+import { describe, test, expect, spyOn } from 'bun:test'
 
 import { create as createPRNG } from 'lib0/prng'
 import * as Y from 'yjs'
@@ -127,6 +127,8 @@ function createSyncedStores(options: SyncedStoreOptions = {}) {
       return peerSuppressGraphSync
     },
     cleanup: () => {
+      hostStore.preparationController.dispose()
+      peerStore.preparationController.dispose()
       disconnectYDocs?.()
       hostDoc.destroy()
       peerDoc.destroy()
@@ -134,10 +136,13 @@ function createSyncedStores(options: SyncedStoreOptions = {}) {
   }
 }
 
-function withSyncedStores(run: (stores: SyncedStores) => void, options: SyncedStoreOptions = {}) {
+async function withSyncedStores(
+  run: (stores: SyncedStores) => void | Promise<void>,
+  options: SyncedStoreOptions = {}
+) {
   const stores = createSyncedStores(options)
   try {
-    run(stores)
+    await run(stores)
   } finally {
     stores.cleanup()
   }
@@ -323,22 +328,52 @@ describe('collab yjs-sync', () => {
     expect(getNodeOrThrow(peer, rect.id).type).toBe('RECTANGLE')
   })
 
-  test('syncAllNodesToYjs populates peer graph and current page', () => {
-    withSyncedStores(({ hostStore, peerStore, hostSync }) => {
+  test('deduplicates a pending page switch and handles its rejection', async () => {
+    await withSyncedStores(async ({ hostStore, peerStore, hostSync }) => {
+      const page = firstPage(hostStore.graph)
+      const node = hostStore.graph.createNode('RECTANGLE', page.id)
+      const { promise: pending, reject: rejectSwitch } = Promise.withResolvers<undefined>()
+      const switchPage = spyOn(peerStore, 'switchPage').mockReturnValue(pending)
+      const log = spyOn(console, 'error').mockImplementation(() => undefined)
+      try {
+        hostSync.syncAllNodesToYjs()
+        hostSync.syncNodeToYjs(node.id)
+        expect(switchPage).toHaveBeenCalledTimes(1)
+        const error = new Error('Page preparation failed')
+        rejectSwitch(error)
+        await pending.catch(() => undefined)
+        await Promise.resolve()
+        expect(log).toHaveBeenCalledWith('[Collab] Failed to switch to a synced page:', error)
+      } finally {
+        switchPage.mockRestore()
+        log.mockRestore()
+      }
+    })
+  })
+
+  test('syncAllNodesToYjs populates peer graph and current page', async () => {
+    await withSyncedStores(async ({ hostStore, peerStore, hostSync }) => {
       const hostPage = firstPage(hostStore.graph)
       const rect = hostStore.graph.createNode('RECTANGLE', hostPage.id, { width: 80, height: 60 })
 
+      const pageChanged = new Promise<void>((resolve) => {
+        const off = peerStore.onEditorEvent('page:changed', () => {
+          off()
+          resolve()
+        })
+      })
       hostSync.syncAllNodesToYjs()
 
       expect(peerStore.graph.rootId).toBe(hostStore.graph.rootId)
+      await pageChanged
       expect(peerStore.state.currentPageId).toBe(hostPage.id)
       expect(peerStore.graph.getPages().map((page) => page.id)).toContain(hostPage.id)
       expect(getNodeOrThrow(peerStore.graph, rect.id).type).toBe('RECTANGLE')
     })
   })
 
-  test('live-created and edited nodes sync in both directions', () => {
-    withSyncedStores(({ hostStore, peerStore, hostSync, peerSync }) => {
+  test('live-created and edited nodes sync in both directions', async () => {
+    await withSyncedStores(({ hostStore, peerStore, hostSync, peerSync }) => {
       const hostPage = firstPage(hostStore.graph)
       hostSync.syncAllNodesToYjs()
 
@@ -357,8 +392,8 @@ describe('collab yjs-sync', () => {
     })
   })
 
-  test('unchanged node synchronization emits no Yjs update', () => {
-    withSyncedStores(({ hostStore, hostSync, hostDoc }) => {
+  test('unchanged node synchronization emits no Yjs update', async () => {
+    await withSyncedStores(({ hostStore, hostSync, hostDoc }) => {
       const hostPage = firstPage(hostStore.graph)
       const rect = hostStore.graph.createNode('RECTANGLE', hostPage.id, { width: 80, height: 60 })
       hostSync.syncNodeToYjs(rect.id)
@@ -378,8 +413,8 @@ describe('collab yjs-sync', () => {
     })
   })
 
-  test('repeated drag-like updates stay field-sized and do not echo', () => {
-    withSyncedStores(({ hostStore, peerStore, hostSync, hostDoc, peerDoc }) => {
+  test('repeated drag-like updates stay field-sized and do not echo', async () => {
+    await withSyncedStores(({ hostStore, peerStore, hostSync, hostDoc, peerDoc }) => {
       const hostPage = firstPage(hostStore.graph)
       const rect = hostStore.graph.createNode('RECTANGLE', hostPage.id, { width: 80, height: 60 })
       hostSync.syncAllNodesToYjs()
@@ -412,13 +447,13 @@ describe('collab yjs-sync', () => {
     })
   })
 
-  test('queued concurrent edits converge through the official Yjs test connector', () => {
+  test('queued concurrent edits converge through the official Yjs test connector', async () => {
     const connector = new TestConnector(createPRNG(526))
     const hostDoc: TestYInstance = connector.createY(1)
     const peerDoc: TestYInstance = connector.createY(2)
     connector.syncAll()
 
-    withSyncedStores(
+    await withSyncedStores(
       ({ hostStore, peerStore, hostSync, peerSync }) => {
         const hostPage = firstPage(hostStore.graph)
         const rect = hostStore.graph.createNode('RECTANGLE', hostPage.id, {
@@ -448,8 +483,8 @@ describe('collab yjs-sync', () => {
     )
   })
 
-  test('image fills sync image bytes', () => {
-    withSyncedStores(({ hostStore, peerStore, hostSync }) => {
+  test('image fills sync image bytes', async () => {
+    await withSyncedStores(({ hostStore, peerStore, hostSync }) => {
       const hostPage = firstPage(hostStore.graph)
       const imageHash = 'image-hash'
       const imageFill: Fill = {
diff --git a/tests/engine/core/editor/text/start-editing-gate.test.ts b/tests/engine/core/editor/text/start-editing-gate.test.ts
index 898265e7f..3b467f4cc 100644
--- a/tests/engine/core/editor/text/start-editing-gate.test.ts
+++ b/tests/engine/core/editor/text/start-editing-gate.test.ts
@@ -20,12 +20,26 @@ describe('startTextEditing — path-text font gate', () => {
     const editor = createEditor()
     const page = editor.state.currentPageId
     const box = { x: 0, y: 0, width: 200, height: 200 }
+    const textPathData = {
+      network: {
+        vertices: [
+          { x: 0, y: 100 },
+          { x: 200, y: 100 }
+        ],
+        segments: [{ start: 0, end: 1, tangentStart: { x: 0, y: 0 }, tangentEnd: { x: 0, y: 0 } }],
+        regions: []
+      },
+      normalizedSize: { x: 200, y: 200 },
+      tValue: 0,
+      forward: true
+    }
 
     // Path text, font AVAILABLE → editable.
     const editable = editor.graph.createNode('TEXT', page, {
       text: 'ab',
       fontFamily: 'Inter',
       fontWeight: 400,
+      textPathData: structuredClone(textPathData),
       textPathBox: { ...box }
     })
     editor.startTextEditing(editable.id)
@@ -37,6 +51,7 @@ describe('startTextEditing — path-text font gate', () => {
       text: 'ab',
       fontFamily: 'NoSuchFont',
       fontWeight: 400,
+      textPathData: structuredClone(textPathData),
       textPathBox: { ...box }
     })
     editor.startTextEditing(baked.id)
diff --git a/tests/engine/tauri/mock-cleanup.test.ts b/tests/engine/tauri/mock-cleanup.test.ts
new file mode 100644
index 000000000..689175d03
--- /dev/null
+++ b/tests/engine/tauri/mock-cleanup.test.ts
@@ -0,0 +1,16 @@
+import { afterEach, expect, test } from 'bun:test'
+
+import { clearTauriMocks, installTauriMockWindow, mockTauriIPC } from '#tests/helpers/tauri/mocks'
+
+afterEach(clearTauriMocks)
+
+test('clearing IPC mocks removes runtime markers before reinstalling a window', async () => {
+  await mockTauriIPC(() => null)
+  expect('__TAURI_INTERNALS__' in window).toBe(true)
+
+  await clearTauriMocks()
+  installTauriMockWindow()
+
+  expect('__TAURI_INTERNALS__' in window).toBe(false)
+  expect('__TAURI_EVENT_PLUGIN_INTERNALS__' in window).toBe(false)
+})
diff --git a/tests/helpers/tauri/mocks.ts b/tests/helpers/tauri/mocks.ts
index eea7cc6be..620992432 100644
--- a/tests/helpers/tauri/mocks.ts
+++ b/tests/helpers/tauri/mocks.ts
@@ -24,5 +24,7 @@ export async function clearTauriMocks() {
   if (!('window' in globalThis)) return
   const { clearMocks } = await import('@tauri-apps/api/mocks')
   clearMocks()
+  Reflect.deleteProperty(window, '__TAURI_INTERNALS__')
+  Reflect.deleteProperty(window, '__TAURI_EVENT_PLUGIN_INTERNALS__')
   delete (globalThis as typeof globalThis & { window?: unknown }).window
 }
diff --git a/tools/unit-tests/src/shards.ts b/tools/unit-tests/src/shards.ts
index 758e810cf..f68323c68 100644
--- a/tools/unit-tests/src/shards.ts
+++ b/tools/unit-tests/src/shards.ts
@@ -5,10 +5,17 @@ import { fileURLToPath } from 'node:url'
 const REPO_ROOT = resolve(dirname(fileURLToPath(import.meta.url)), '../../..')
 
 export const UNIT_TEST_GROUPS = {
-  app: ['tests/engine/acp', 'tests/engine/app', 'tests/engine/cli', 'tests/engine/tauri'],
+  app: [
+    'tests/engine/acp',
+    'tests/engine/app',
+    'tests/engine/cli',
+    'tests/engine/collab',
+    'tests/engine/tauri'
+  ],
   dom: ['tests/engine/dom-css', 'tests/engine/color', 'tests/engine/icons', 'tests/engine/pen'],
   editor: [
     'tests/engine/clipboard',
+    'tests/engine/core',
     'tests/engine/editor',
     'tests/engine/hit-test',
     'tests/engine/snap'
@@ -16,6 +23,8 @@ export const UNIT_TEST_GROUPS = {
   fig: ['tests/engine/figma', 'tests/engine/io', 'tests/engine/kiwi'],
   render: ['tests/engine/geometry', 'tests/engine/layout', 'tests/engine/render'],
   scene: [
+    'tests/engine/bytes',
+    'tests/engine/library',
     'tests/engine/lint',
     'tests/engine/random',
     'tests/engine/scene-graph',
diff --git a/tools/unit-tests/tests/shards.test.ts b/tools/unit-tests/tests/shards.test.ts
index 385f449e5..5b0e953f5 100644
--- a/tools/unit-tests/tests/shards.test.ts
+++ b/tools/unit-tests/tests/shards.test.ts
@@ -1,4 +1,5 @@
 import { expect, test } from 'bun:test'
+import { fileURLToPath } from 'node:url'
 
 import {
   isHeavyUnitTest,
@@ -8,6 +9,32 @@ import {
   unitTestGroupNames
 } from '../src/shards'
 
+test('every engine test belongs to exactly one shard', async () => {
+  const discovered = await Array.fromAsync(
+    new Bun.Glob('tests/engine/**/*.test.ts').scan({
+      cwd: fileURLToPath(new URL('../../..', import.meta.url))
+    })
+  )
+  const paths = pathsForUnitTestGroup('all')
+  const invalidAssignments = discovered.flatMap((file) => {
+    const owners = paths.filter((path) => file.startsWith(`${path}/`))
+    return owners.length === 1 ? [] : [{ file, owners }]
+  })
+
+  expect(discovered.length).toBeGreaterThan(0)
+  expect(invalidAssignments).toEqual([])
+  expect((await listUnitTests('all', { includeHeavy: true })).sort()).toEqual(discovered.sort())
+})
+
+test('quick and explicit heavy tests partition the full engine suite', async () => {
+  const quick = await listUnitTests('all')
+  const heavy = await listHeavyUnitTests()
+  const all = await listUnitTests('all', { includeHeavy: true })
+
+  expect(quick.filter((file) => heavy.includes(file))).toEqual([])
+  expect([...quick, ...heavy].sort()).toEqual(all)
+})
+
 test('unit test groups cover all declared shards', () => {
   expect(unitTestGroupNames()).toContain('all')
   expect(pathsForUnitTestGroup('dom')).toContain('tests/engine/dom-css')