diff --git a/oxlint.json b/oxlint.json
index c5ec31773..bcec1f5d8 100644
--- a/oxlint.json
+++ b/oxlint.json
@@ -162,12 +162,6 @@
         "open-pencil/no-useless-pass-through-wrappers": "error"
       }
     },
-    {
-      "files": ["tests/**/*.ts", "tests/**/*.tsx"],
-      "rules": {
-        "typescript/no-non-null-assertion": "off"
-      }
-    },
     {
       "files": ["**/kiwi/kiwi-schema/**"],
       "rules": {
diff --git a/tests/e2e/canvas/manipulation.spec.ts b/tests/e2e/canvas/manipulation.spec.ts
index 6bee1603e..5f9db05a7 100644
--- a/tests/e2e/canvas/manipulation.spec.ts
+++ b/tests/e2e/canvas/manipulation.spec.ts
@@ -1,5 +1,6 @@
 import { test, expect, type Page } from '@playwright/test'
 
+import { expectDefined } from '#tests/helpers/assert'
 import { CanvasHelper } from '#tests/helpers/canvas'
 import { getSelectedIds, getPageChildren, getSelectedNode, getNodeById } from '#tests/helpers/store'
 
@@ -106,8 +107,8 @@ test('resize corner handle drag increases node dimensions', async () => {
   const box = await page.locator('[data-test-id="canvas-element"]').boundingBox()
   if (!box) throw new Error('No canvas')
 
-  const hx = box.x + viewport!.handleX
-  const hy = box.y + viewport!.handleY
+  const hx = box.x + expectDefined(viewport, 'viewport state').handleX
+  const hy = box.y + expectDefined(viewport, 'viewport state').handleY
 
   await page.mouse.move(hx, hy)
   await page.mouse.down()
@@ -116,8 +117,12 @@ test('resize corner handle drag increases node dimensions', async () => {
   await canvas.waitForRender()
 
   const after = await getSelectedNode(page)
-  expect(after!.width).toBeGreaterThan(before!.width + 20)
-  expect(after!.height).toBeGreaterThan(before!.height + 20)
+  expect(expectDefined(after, 'selected node after').width).toBeGreaterThan(
+    expectDefined(before, 'selected node before').width + 20
+  )
+  expect(expectDefined(after, 'selected node after').height).toBeGreaterThan(
+    expectDefined(before, 'selected node before').height + 20
+  )
   canvas.assertNoErrors()
 })
 
@@ -129,7 +134,7 @@ test('rotation handle drag rotates node', async () => {
 
   const before = await getSelectedNode(page)
   expect(before).not.toBeNull()
-  const initialRotation = before!.rotation ?? 0
+  const initialRotation = expectDefined(before, 'selected node before').rotation ?? 0
 
   const viewport = await page.evaluate(() => {
     const store = window.openPencil?.store
@@ -150,8 +155,8 @@ test('rotation handle drag rotates node', async () => {
   const box = await page.locator('[data-test-id="canvas-element"]').boundingBox()
   if (!box) throw new Error('No canvas')
 
-  const rx = box.x + viewport!.cx
-  const ry = box.y + viewport!.topMidY - 24
+  const rx = box.x + expectDefined(viewport, 'viewport state').cx
+  const ry = box.y + expectDefined(viewport, 'viewport state').topMidY - 24
 
   await page.mouse.move(rx, ry)
   await canvas.waitForRender()
@@ -160,8 +165,8 @@ test('rotation handle drag rotates node', async () => {
   await page.mouse.up()
   await canvas.waitForRender()
 
-  const after = await getNodeById(page, before!.id)
-  expect(after!.rotation ?? 0).not.toBe(initialRotation)
+  const after = await getNodeById(page, expectDefined(before, 'selected node before').id)
+  expect(expectDefined(after, 'selected node after').rotation ?? 0).not.toBe(initialRotation)
   canvas.assertNoErrors()
 })
 
@@ -236,14 +241,20 @@ async function setupFrameChild(rotation: number) {
   })
 
   expect(state).not.toBeNull()
-  return state!
+  return expectDefined(state, 'frame child state')
 }
 
 test('frame children keep correct hover and click hit area without rotation', async () => {
   const state = await setupFrameChild(0)
 
   await canvas.hover(state.hitX, state.hitY)
-  const hoveredId = await page.evaluate(() => window.openPencil?.store!.state.hoveredNodeId)
+  const hoveredId = await page.evaluate(() =>
+    (() => {
+      const store = window.openPencil?.store
+      if (!store) throw new Error('OpenPencil store not initialized')
+      return store.state.hoveredNodeId
+    })()
+  )
   expect(hoveredId).toBe(state.childId)
 
   await canvas.click(state.hitX, state.hitY)
@@ -252,7 +263,13 @@ test('frame children keep correct hover and click hit area without rotation', as
   expect(selected?.id).toBe(state.childId)
 
   await canvas.hover(state.missX, state.missY)
-  const hoveredMiss = await page.evaluate(() => window.openPencil?.store!.state.hoveredNodeId)
+  const hoveredMiss = await page.evaluate(() =>
+    (() => {
+      const store = window.openPencil?.store
+      if (!store) throw new Error('OpenPencil store not initialized')
+      return store.state.hoveredNodeId
+    })()
+  )
   expect(hoveredMiss).not.toBe(state.childId)
   canvas.assertNoErrors()
 })
@@ -261,7 +278,13 @@ test('rotated frame children keep correct hover and click hit area', async () =>
   const state = await setupFrameChild(35)
 
   await canvas.hover(state.hitX, state.hitY)
-  const hoveredId = await page.evaluate(() => window.openPencil?.store!.state.hoveredNodeId)
+  const hoveredId = await page.evaluate(() =>
+    (() => {
+      const store = window.openPencil?.store
+      if (!store) throw new Error('OpenPencil store not initialized')
+      return store.state.hoveredNodeId
+    })()
+  )
   expect(hoveredId).toBe(state.childId)
 
   await canvas.click(state.hitX, state.hitY)
@@ -270,7 +293,13 @@ test('rotated frame children keep correct hover and click hit area', async () =>
   expect(selected?.id).toBe(state.childId)
 
   await canvas.hover(state.missX, state.missY)
-  const hoveredMiss = await page.evaluate(() => window.openPencil?.store!.state.hoveredNodeId)
+  const hoveredMiss = await page.evaluate(() =>
+    (() => {
+      const store = window.openPencil?.store
+      if (!store) throw new Error('OpenPencil store not initialized')
+      return store.state.hoveredNodeId
+    })()
+  )
   expect(hoveredMiss).not.toBe(state.childId)
   canvas.assertNoErrors()
 })
@@ -300,8 +329,8 @@ test('rotation drag exposes live rotation preview state', async () => {
   const box = await page.locator('[data-test-id="canvas-element"]').boundingBox()
   if (!box) throw new Error('No canvas')
 
-  const rx = box.x + viewport!.cx
-  const ry = box.y + viewport!.topMidY - 24
+  const rx = box.x + expectDefined(viewport, 'viewport state').cx
+  const ry = box.y + expectDefined(viewport, 'viewport state').topMidY - 24
 
   await page.mouse.move(rx, ry)
   await canvas.waitForRender()
@@ -309,13 +338,25 @@ test('rotation drag exposes live rotation preview state', async () => {
   await page.mouse.move(rx + 60, ry + 60, { steps: 15 })
   await canvas.waitForRender()
 
-  const preview = await page.evaluate(() => window.openPencil?.store!.state.rotationPreview)
+  const preview = await page.evaluate(() =>
+    (() => {
+      const store = window.openPencil?.store
+      if (!store) throw new Error('OpenPencil store not initialized')
+      return store.state.rotationPreview
+    })()
+  )
   expect(preview).not.toBeNull()
 
   await page.mouse.up()
   await canvas.waitForRender()
 
-  const clearedPreview = await page.evaluate(() => window.openPencil?.store!.state.rotationPreview)
+  const clearedPreview = await page.evaluate(() =>
+    (() => {
+      const store = window.openPencil?.store
+      if (!store) throw new Error('OpenPencil store not initialized')
+      return store.state.rotationPreview
+    })()
+  )
   expect(clearedPreview).toBeNull()
   canvas.assertNoErrors()
 })
diff --git a/tests/e2e/design/panel.spec.ts b/tests/e2e/design/panel.spec.ts
index 22a880066..efe8ab95f 100644
--- a/tests/e2e/design/panel.spec.ts
+++ b/tests/e2e/design/panel.spec.ts
@@ -1,5 +1,6 @@
 import { expect, test, type Page } from '@playwright/test'
 
+import { expectDefined } from '#tests/helpers/assert'
 import { CanvasHelper } from '#tests/helpers/canvas'
 
 let page: Page
@@ -102,7 +103,7 @@ test('fill item shows color swatch', async () => {
 
 test('clicking color area changes fill color', async () => {
   const id = await getSelectedId()
-  const before = await getNode(id!)
+  const before = await getNode(expectDefined(id, 'selected id'))
 
   const swatch = fillSection().locator('[data-test-id="fill-picker-swatch"]').first()
   await swatch.click()
@@ -111,13 +112,16 @@ test('clicking color area changes fill color', async () => {
   await expect(colorArea).toBeVisible({ timeout: 5000 })
 
   const box = await colorArea.boundingBox()
-  await page.mouse.click(box!.x + box!.width - 10, box!.y + 10)
+  await page.mouse.click(
+    expectDefined(box, 'color area bounds').x + expectDefined(box, 'color area bounds').width - 10,
+    expectDefined(box, 'color area bounds').y + 10
+  )
   await canvas.waitForRender()
   await page.waitForTimeout(100)
 
-  const after = await getNode(id!)
-  const c1 = before!.fills[0].color
-  const c2 = after!.fills[0].color
+  const after = await getNode(expectDefined(id, 'selected id'))
+  const c1 = expectDefined(before, 'before node').fills[0].color
+  const c2 = expectDefined(after, 'after node').fills[0].color
   expect(c1.r !== c2.r || c1.g !== c2.g || c1.b !== c2.b).toBe(true)
 
   // Close popover — click the swatch again to toggle it off
@@ -134,8 +138,8 @@ test('adding a stroke creates stroke section item', async () => {
   await expect(strokeItems.first()).toBeVisible()
 
   const id = await getSelectedId()
-  const node = await getNode(id!)
-  expect(node!.strokes.length).toBe(1)
+  const node = await getNode(expectDefined(id, 'selected id'))
+  expect(expectDefined(node, 'node node').strokes.length).toBe(1)
 })
 
 test('adding an effect creates effect item', async () => {
@@ -147,8 +151,8 @@ test('adding an effect creates effect item', async () => {
   await expect(effectItems.first()).toBeVisible()
 
   const id = await getSelectedId()
-  const node = await getNode(id!)
-  expect(node!.effects.length).toBe(1)
+  const node = await getNode(expectDefined(id, 'selected id'))
+  expect(expectDefined(node, 'node node').effects.length).toBe(1)
 })
 
 test('adding a second fill shows two fill items', async () => {
@@ -160,8 +164,8 @@ test('adding a second fill shows two fill items', async () => {
   expect(await fillItems.count()).toBe(2)
 
   const id = await getSelectedId()
-  const node = await getNode(id!)
-  expect(node!.fills.length).toBe(2)
+  const node = await getNode(expectDefined(id, 'selected id'))
+  expect(expectDefined(node, 'node node').fills.length).toBe(2)
 })
 
 test('visibility toggle in appearance section works', async () => {
@@ -169,20 +173,20 @@ test('visibility toggle in appearance section works', async () => {
   await expect(visBtn).toBeVisible()
 
   const id = await getSelectedId()
-  const before = await getNode(id!)
-  expect(before!.visible).toBe(true)
+  const before = await getNode(expectDefined(id, 'selected id'))
+  expect(expectDefined(before, 'before node').visible).toBe(true)
 
   await visBtn.click()
   await canvas.waitForRender()
 
-  const after = await getNode(id!)
-  expect(after!.visible).toBe(false)
+  const after = await getNode(expectDefined(id, 'selected id'))
+  expect(expectDefined(after, 'after node').visible).toBe(false)
 
   await visBtn.click()
   await canvas.waitForRender()
 
-  const restored = await getNode(id!)
-  expect(restored!.visible).toBe(true)
+  const restored = await getNode(expectDefined(id, 'selected id'))
+  expect(expectDefined(restored, 'restored node').visible).toBe(true)
 })
 
 test('fill stroke and effect visibility toggles update on repeated clicks and support undo redo', async () => {
@@ -192,23 +196,35 @@ test('fill stroke and effect visibility toggles update on repeated clicks and su
   const fillButton = page.locator('[data-test-id="fill-visibility-0"]')
   await expect(fillButton).toBeVisible()
 
-  const initial = await getNode(id!)
-  expect(initial!.fills[0]?.visible).toBe(true)
+  const initial = await getNode(expectDefined(id, 'selected id'))
+  expect(expectDefined(initial, 'initial node').fills[0]?.visible).toBe(true)
 
   await fillButton.click()
   await canvas.waitForRender()
   await expect(fillButton).toHaveAttribute('data-visible', 'false')
-  expect((await getNode(id!))!.fills[0]?.visible).toBe(false)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').fills[0]
+      ?.visible
+  ).toBe(false)
 
   await fillButton.click()
   await canvas.waitForRender()
   await expect(fillButton).toHaveAttribute('data-visible', 'true')
-  expect((await getNode(id!))!.fills[0]?.visible).toBe(true)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').fills[0]
+      ?.visible
+  ).toBe(true)
 
   await canvas.undo()
-  expect((await getNode(id!))!.fills[0]?.visible).toBe(false)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').fills[0]
+      ?.visible
+  ).toBe(false)
   await canvas.redo()
-  expect((await getNode(id!))!.fills[0]?.visible).toBe(true)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').fills[0]
+      ?.visible
+  ).toBe(true)
 
   const strokeAddButton = strokeSection().locator('[data-test-id="stroke-section-add"]')
   await strokeAddButton.click()
@@ -216,22 +232,37 @@ test('fill stroke and effect visibility toggles update on repeated clicks and su
 
   const strokeButton = page.locator('[data-test-id="stroke-visibility-0"]')
   await expect(strokeButton).toBeVisible()
-  expect((await getNode(id!))!.strokes[0]?.visible).toBe(true)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').strokes[0]
+      ?.visible
+  ).toBe(true)
 
   await strokeButton.click()
   await canvas.waitForRender()
   await expect(strokeButton).toHaveAttribute('data-visible', 'false')
-  expect((await getNode(id!))!.strokes[0]?.visible).toBe(false)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').strokes[0]
+      ?.visible
+  ).toBe(false)
 
   await strokeButton.click()
   await canvas.waitForRender()
   await expect(strokeButton).toHaveAttribute('data-visible', 'true')
-  expect((await getNode(id!))!.strokes[0]?.visible).toBe(true)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').strokes[0]
+      ?.visible
+  ).toBe(true)
 
   await canvas.undo()
-  expect((await getNode(id!))!.strokes[0]?.visible).toBe(false)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').strokes[0]
+      ?.visible
+  ).toBe(false)
   await canvas.redo()
-  expect((await getNode(id!))!.strokes[0]?.visible).toBe(true)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').strokes[0]
+      ?.visible
+  ).toBe(true)
 
   const effectAddButton = effectsSection().locator('[data-test-id="effects-section-add"]')
   await effectAddButton.click()
@@ -239,22 +270,37 @@ test('fill stroke and effect visibility toggles update on repeated clicks and su
 
   const effectButton = page.locator('[data-test-id="effect-visibility-0"]')
   await expect(effectButton).toBeVisible()
-  expect((await getNode(id!))!.effects[0]?.visible).toBe(true)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').effects[0]
+      ?.visible
+  ).toBe(true)
 
   await effectButton.click()
   await canvas.waitForRender()
   await expect(effectButton).toHaveAttribute('data-visible', 'false')
-  expect((await getNode(id!))!.effects[0]?.visible).toBe(false)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').effects[0]
+      ?.visible
+  ).toBe(false)
 
   await effectButton.click()
   await canvas.waitForRender()
   await expect(effectButton).toHaveAttribute('data-visible', 'true')
-  expect((await getNode(id!))!.effects[0]?.visible).toBe(true)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').effects[0]
+      ?.visible
+  ).toBe(true)
 
   await canvas.undo()
-  expect((await getNode(id!))!.effects[0]?.visible).toBe(false)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').effects[0]
+      ?.visible
+  ).toBe(false)
   await canvas.redo()
-  expect((await getNode(id!))!.effects[0]?.visible).toBe(true)
+  expect(
+    expectDefined(await getNode(expectDefined(id, 'selected id')), 'selected node').effects[0]
+      ?.visible
+  ).toBe(true)
 })
 
 test('deselecting shows empty design panel', async () => {
diff --git a/tests/e2e/editor/auto-layout.spec.ts b/tests/e2e/editor/auto-layout.spec.ts
index 8ba7874ce..6b17dd247 100644
--- a/tests/e2e/editor/auto-layout.spec.ts
+++ b/tests/e2e/editor/auto-layout.spec.ts
@@ -1,5 +1,6 @@
 import { test, expect, type Page } from '@playwright/test'
 
+import { expectDefined } from '#tests/helpers/assert'
 import { CanvasHelper } from '#tests/helpers/canvas'
 import { getSelectedNode, getNodeById } from '#tests/helpers/store'
 
@@ -24,7 +25,9 @@ test.afterAll(async () => {
 async function selectFrame() {
   expect(frameId, 'frameId must be set — did the Shift+A test run?').toBeTruthy()
   await page.evaluate((id: string) => {
-    window.openPencil?.store!.select([id])
+    const store = window.openPencil?.store
+    if (!store) throw new Error('OpenPencil store not initialized')
+    store.select([id])
   }, frameId)
   await canvas.waitForRender()
 }
@@ -41,11 +44,11 @@ test('Shift+A wraps selection in auto-layout frame', async () => {
 
   const node = await getSelectedNode(page)
   expect(node).not.toBeNull()
-  expect(node!.type).toBe('FRAME')
-  expect(node!.layoutMode).not.toBe('NONE')
-  expect(node!.childIds.length).toBe(2)
+  expect(expectDefined(node, 'node').type).toBe('FRAME')
+  expect(expectDefined(node, 'node').layoutMode).not.toBe('NONE')
+  expect(expectDefined(node, 'node').childIds.length).toBe(2)
 
-  frameId = node!.id
+  frameId = expectDefined(node, 'node').id
   canvas.assertNoErrors()
 })
 
@@ -56,19 +59,19 @@ test('direction button toggles to VERTICAL', async () => {
   await canvas.waitForRender()
 
   const frame = await getNodeById(page, frameId)
-  expect(frame!.layoutMode).toBe('VERTICAL')
+  expect(expectDefined(frame, 'frame').layoutMode).toBe('VERTICAL')
   canvas.assertNoErrors()
 })
 
 test('gap ScrubInput sets itemSpacing', async () => {
   await selectFrame()
   const before = await getNodeById(page, frameId)
-  const initialSpacing = before!.itemSpacing
+  const initialSpacing = expectDefined(before, 'before').itemSpacing
 
   await canvas.dragScrubInput(page.locator('[data-test-id="layout-gap-input"]'), 40)
 
   const after = await getNodeById(page, frameId)
-  expect(after!.itemSpacing).toBeGreaterThan(initialSpacing + 5)
+  expect(expectDefined(after, 'after').itemSpacing).toBeGreaterThan(initialSpacing + 5)
   canvas.assertNoErrors()
 })
 
@@ -79,15 +82,17 @@ test('gap menu sets auto space-between alignment', async () => {
   await page.getByRole('option', { name: 'Auto' }).click()
   await canvas.waitForRender()
   let frame = await getNodeById(page, frameId)
-  expect(frame!.primaryAxisAlign).toBe('SPACE_BETWEEN')
+  expect(expectDefined(frame, 'frame').primaryAxisAlign).toBe('SPACE_BETWEEN')
   await expect(page.locator('[data-test-id="layout-alignment-grid"] button')).toHaveCount(9)
 
   await page.locator('[data-test-id="layout-gap-menu"]').click()
-  await page.getByRole('option', { name: String(Math.round(frame!.itemSpacing)) }).click()
+  await page
+    .getByRole('option', { name: String(Math.round(expectDefined(frame, 'frame').itemSpacing)) })
+    .click()
   await canvas.waitForRender()
 
   frame = await getNodeById(page, frameId)
-  expect(frame!.primaryAxisAlign).toBe('MIN')
+  expect(expectDefined(frame, 'frame').primaryAxisAlign).toBe('MIN')
   await expect(page.locator('[data-test-id="layout-alignment-grid"] button')).toHaveCount(9)
   canvas.assertNoErrors()
 })
@@ -99,12 +104,12 @@ test('wrap mode exposes cross-axis gap control', async () => {
   await canvas.waitForRender()
 
   const before = await getNodeById(page, frameId)
-  const initialSpacing = before!.counterAxisSpacing
+  const initialSpacing = expectDefined(before, 'before').counterAxisSpacing
   await canvas.dragScrubInput(page.locator('[data-test-id="layout-cross-gap-input"]'), 40)
 
   const after = await getNodeById(page, frameId)
-  expect(after!.layoutWrap).toBe('WRAP')
-  expect(after!.counterAxisSpacing).toBeGreaterThan(initialSpacing + 5)
+  expect(expectDefined(after, 'after').layoutWrap).toBe('WRAP')
+  expect(expectDefined(after, 'after').counterAxisSpacing).toBeGreaterThan(initialSpacing + 5)
   canvas.assertNoErrors()
 })
 
@@ -130,10 +135,10 @@ test('padding controls set horizontal and vertical padding pairs', async () => {
   await canvas.waitForRender()
 
   const frame = await getNodeById(page, frameId)
-  expect(frame!.paddingTop).toBe(16)
-  expect(frame!.paddingRight).toBe(24)
-  expect(frame!.paddingBottom).toBe(16)
-  expect(frame!.paddingLeft).toBe(24)
+  expect(expectDefined(frame, 'frame').paddingTop).toBe(16)
+  expect(expectDefined(frame, 'frame').paddingRight).toBe(24)
+  expect(expectDefined(frame, 'frame').paddingBottom).toBe(16)
+  expect(expectDefined(frame, 'frame').paddingLeft).toBe(24)
   canvas.assertNoErrors()
 })
 
@@ -145,7 +150,9 @@ test('size dropdown adds and removes min width', async () => {
   await canvas.waitForRender()
 
   let frame = await getNodeById(page, frameId)
-  expect(frame!.minWidth).toBe(Math.round(frame!.width))
+  expect(expectDefined(frame, 'frame').minWidth).toBe(
+    Math.round(expectDefined(frame, 'frame').width)
+  )
   await expect(page.locator('[data-test-id="layout-min-width-input"]')).toBeVisible()
 
   await page.locator('[data-test-id="layout-width-sizing-menu"]').click()
@@ -153,7 +160,7 @@ test('size dropdown adds and removes min width', async () => {
   await canvas.waitForRender()
 
   frame = await getNodeById(page, frameId)
-  expect(frame!.minWidth).toBeNull()
+  expect(expectDefined(frame, 'frame').minWidth).toBeNull()
   await expect(page.locator('[data-test-id="layout-min-width-input"]')).toHaveCount(0)
   canvas.assertNoErrors()
 })
@@ -166,8 +173,8 @@ test('alignment grid center sets CENTER alignment', async () => {
   await canvas.waitForRender()
 
   const frame = await getNodeById(page, frameId)
-  expect(frame!.primaryAxisAlign).toBe('CENTER')
-  expect(frame!.counterAxisAlign).toBe('CENTER')
+  expect(expectDefined(frame, 'frame').primaryAxisAlign).toBe('CENTER')
+  expect(expectDefined(frame, 'frame').counterAxisAlign).toBe('CENTER')
   canvas.assertNoErrors()
 })
 
@@ -178,6 +185,6 @@ test('remove auto-layout sets layoutMode to NONE', async () => {
   await canvas.waitForRender()
 
   const frame = await getNodeById(page, frameId)
-  expect(frame!.layoutMode).toBe('NONE')
+  expect(expectDefined(frame, 'frame').layoutMode).toBe('NONE')
   canvas.assertNoErrors()
 })
diff --git a/tests/engine/editor/clipboard/import-nodes.test.ts b/tests/engine/editor/clipboard/import-nodes.test.ts
index 046c5d2bb..5e4a251db 100644
--- a/tests/engine/editor/clipboard/import-nodes.test.ts
+++ b/tests/engine/editor/clipboard/import-nodes.test.ts
@@ -3,6 +3,7 @@ import { describe, expect, it } from 'bun:test'
 import { importClipboardNodes } from '@open-pencil/core'
 import type { NodeChange, SceneNode } from '@open-pencil/core'
 
+import { getNodeOrThrow } from '#tests/helpers/assert'
 import { createClipboardGraph } from '#tests/helpers/clipboard'
 
 describe('importClipboardNodes', () => {
@@ -52,7 +53,7 @@ describe('importClipboardNodes', () => {
     const created = importClipboardNodes(nodeChanges, graph, pageId)
     expect(created).toHaveLength(1)
 
-    const card = graph.getNode(created[0])!
+    const card = getNodeOrThrow(graph, created[0])
     expect(card.type).toBe('FRAME')
     expect(card.name).toBe('Card')
 
@@ -109,7 +110,7 @@ describe('importClipboardNodes', () => {
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
     expect(created).toHaveLength(1)
-    expect(graph.getNode(created[0])!.name).toBe('RealShape')
+    expect(getNodeOrThrow(graph, created[0]).name).toBe('RealShape')
   })
 
   it('imports nested frames with children', () => {
@@ -154,7 +155,7 @@ describe('importClipboardNodes', () => {
     const created = importClipboardNodes(nodeChanges, graph, pageId)
     expect(created).toHaveLength(1)
 
-    const outer = graph.getNode(created[0])!
+    const outer = getNodeOrThrow(graph, created[0])
     expect(outer.name).toBe('Outer')
 
     const innerList = graph.getChildren(outer.id)
@@ -196,7 +197,7 @@ describe('importClipboardNodes', () => {
     ] as NodeChange[]
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    const node = graph.getNode(created[0])!
+    const node = getNodeOrThrow(graph, created[0])
     expect(node.fills).toHaveLength(1)
     expect(node.fills[0].color.r).toBe(1)
     expect(node.strokes).toHaveLength(1)
@@ -244,7 +245,7 @@ describe('importClipboardNodes', () => {
     ] as NodeChange[]
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    const row = graph.getNode(created[0])!
+    const row = getNodeOrThrow(graph, created[0])
     const children = graph.getChildren(row.id)
     expect(children[0].layoutAlignSelf).toBe('STRETCH')
     expect(children[1].layoutAlignSelf).toBe('AUTO')
@@ -290,9 +291,9 @@ describe('importClipboardNodes', () => {
     ] as NodeChange[]
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    expect(graph.getNode(created[0])!.clipsContent).toBe(true)
-    expect(graph.getNode(created[1])!.clipsContent).toBe(false)
-    expect(graph.getNode(created[2])!.clipsContent).toBe(false)
+    expect(getNodeOrThrow(graph, created[0]).clipsContent).toBe(true)
+    expect(getNodeOrThrow(graph, created[1]).clipsContent).toBe(false)
+    expect(getNodeOrThrow(graph, created[2]).clipsContent).toBe(false)
   })
 
   it('imports fontWeight from fontName.style via styleToWeight', () => {
@@ -342,10 +343,10 @@ describe('importClipboardNodes', () => {
     ] as NodeChange[]
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    expect(graph.getNode(created[0])!.fontWeight).toBe(500)
-    expect(graph.getNode(created[1])!.fontWeight).toBe(700)
-    expect(graph.getNode(created[2])!.fontWeight).toBe(700)
-    expect(graph.getNode(created[2])!.italic).toBe(true)
+    expect(getNodeOrThrow(graph, created[0]).fontWeight).toBe(500)
+    expect(getNodeOrThrow(graph, created[1]).fontWeight).toBe(700)
+    expect(getNodeOrThrow(graph, created[2]).fontWeight).toBe(700)
+    expect(getNodeOrThrow(graph, created[2]).italic).toBe(true)
   })
 
   it('converts letterSpacing object to pixels', () => {
@@ -394,9 +395,9 @@ describe('importClipboardNodes', () => {
     ] as NodeChange[]
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    expect(graph.getNode(created[0])!.letterSpacing).toBe(2)
-    expect(graph.getNode(created[1])!.letterSpacing).toBe(2) // 10% of 20px
-    expect(graph.getNode(created[2])!.letterSpacing).toBe(0)
+    expect(getNodeOrThrow(graph, created[0]).letterSpacing).toBe(2)
+    expect(getNodeOrThrow(graph, created[1]).letterSpacing).toBe(2) // 10% of 20px
+    expect(getNodeOrThrow(graph, created[2]).letterSpacing).toBe(0)
   })
 
   it('converts RAW lineHeight to pixels', () => {
@@ -446,9 +447,9 @@ describe('importClipboardNodes', () => {
     ] as NodeChange[]
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    expect(graph.getNode(created[0])!.lineHeight).toBe(36) // 24 * 1.5
-    expect(graph.getNode(created[1])!.lineHeight).toBe(20)
-    expect(graph.getNode(created[2])!.lineHeight).toBe(24) // 120% of 20
+    expect(getNodeOrThrow(graph, created[0]).lineHeight).toBe(36) // 24 * 1.5
+    expect(getNodeOrThrow(graph, created[1]).lineHeight).toBe(20)
+    expect(getNodeOrThrow(graph, created[2]).lineHeight).toBe(24) // 120% of 20
   })
 
   it('converts letterSpacing and lineHeight in style overrides', () => {
@@ -487,7 +488,7 @@ describe('importClipboardNodes', () => {
     ] as NodeChange[]
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    const node = graph.getNode(created[0])!
+    const node = getNodeOrThrow(graph, created[0])
     expect(node.styleRuns).toHaveLength(1)
     expect(node.styleRuns[0].style.lineHeight).toBe(30) // 20 * 1.5
     expect(node.styleRuns[0].style.letterSpacing).toBeCloseTo(-0.4) // 20 * -2/100
@@ -542,7 +543,7 @@ describe('importClipboardNodes', () => {
     const created = importClipboardNodes(nodeChanges, graph, pageId)
     expect(created).toHaveLength(1)
 
-    const component = graph.getNode(created[0])!
+    const component = getNodeOrThrow(graph, created[0])
     expect(component.type).toBe('COMPONENT')
     expect(component.layoutMode).toBe('VERTICAL')
     expect(component.itemSpacing).toBe(16)
@@ -598,11 +599,11 @@ describe('importClipboardNodes', () => {
     const created = importClipboardNodes(nodeChanges, graph, pageId)
     expect(created).toHaveLength(2)
 
-    const component = graph.getNode(created[0])!
+    const component = getNodeOrThrow(graph, created[0])
     expect(component.type).toBe('COMPONENT')
     expect(graph.getChildren(component.id)).toHaveLength(1)
 
-    const instance = graph.getNode(created[1])!
+    const instance = getNodeOrThrow(graph, created[1])
     expect(instance.type).toBe('INSTANCE')
     expect(instance.componentId).toBe(component.id)
 
@@ -662,7 +663,7 @@ describe('importClipboardNodes', () => {
     const created = importClipboardNodes(nodeChanges, graph, pageId)
     expect(created).toHaveLength(1)
 
-    const instance = graph.getNode(created[0])!
+    const instance = getNodeOrThrow(graph, created[0])
     expect(instance.type).toBe('INSTANCE')
     expect(instance.name).toBe('Icon')
 
@@ -717,7 +718,7 @@ describe('importClipboardNodes', () => {
     const created = importClipboardNodes(nodeChanges, graph, pageId)
     expect(created).toHaveLength(1)
 
-    const card = graph.getNode(created[0])!
+    const card = getNodeOrThrow(graph, created[0])
     const children = graph.getChildren(card.id)
     expect(children).toHaveLength(1)
 
@@ -792,7 +793,7 @@ describe('importClipboardNodes', () => {
     const created = importClipboardNodes(nodeChanges, graph, pageId)
     expect(created).toHaveLength(1)
 
-    const instance = graph.getNode(created[0])!
+    const instance = getNodeOrThrow(graph, created[0])
     expect(instance.type).toBe('INSTANCE')
     const children = graph.getChildren(instance.id)
     expect(children).toHaveLength(1)
@@ -845,9 +846,9 @@ describe('importClipboardNodes', () => {
     ] as NodeChange[]
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    expect(graph.getNode(created[0])!.textAutoResize).toBe('HEIGHT')
-    expect(graph.getNode(created[1])!.textAutoResize).toBe('WIDTH_AND_HEIGHT')
-    expect(graph.getNode(created[2])!.textAutoResize).toBe('NONE')
+    expect(getNodeOrThrow(graph, created[0]).textAutoResize).toBe('HEIGHT')
+    expect(getNodeOrThrow(graph, created[1]).textAutoResize).toBe('WIDTH_AND_HEIGHT')
+    expect(getNodeOrThrow(graph, created[2]).textAutoResize).toBe('NONE')
   })
 
   it('undo removes all imported nodes including children', () => {
@@ -940,11 +941,11 @@ describe('importClipboardNodes', () => {
 
     const childrenBefore = graph.getChildren(pageId).length
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    const parent = graph.getNode(created[0])!
+    const parent = getNodeOrThrow(graph, created[0])
 
     const allSnapshots: SceneNode[] = []
     function walk(id: string) {
-      const n = graph.getNode(id)!
+      const n = getNodeOrThrow(graph, id)
       allSnapshots.push({ ...n })
       for (const cid of n.childIds) walk(cid)
     }
@@ -962,7 +963,7 @@ describe('importClipboardNodes', () => {
       })
     }
 
-    const restored = graph.getNode(parent.id)!
+    const restored = getNodeOrThrow(graph, parent.id)
     expect(restored).toBeTruthy()
     expect(restored.name).toBe('Parent')
     expect(restored.childIds).toHaveLength(2)
@@ -1003,11 +1004,11 @@ describe('importClipboardNodes', () => {
     ] as NodeChange[]
 
     const created = importClipboardNodes(nodeChanges, graph, pageId)
-    const parent = graph.getNode(created[0])!
+    const parent = getNodeOrThrow(graph, created[0])
 
     const allSnapshots: SceneNode[] = []
     function walk(id: string) {
-      const n = graph.getNode(id)!
+      const n = getNodeOrThrow(graph, id)
       allSnapshots.push({ ...n })
       for (const cid of n.childIds) walk(cid)
     }
@@ -1020,7 +1021,7 @@ describe('importClipboardNodes', () => {
       graph.createNode(snapshot.type, snapshot.parentId ?? pageId, snapshot)
     }
 
-    const restored = graph.getNode(parent.id)!
+    const restored = getNodeOrThrow(graph, parent.id)
     // Bug: parent has duplicated childIds because snapshot already had [childId]
     // and createNode appends childId again
     expect(restored.childIds.length).toBeGreaterThan(1)
diff --git a/tests/engine/hit-test/scope.test.ts b/tests/engine/hit-test/scope.test.ts
index 729320586..c959058ad 100644
--- a/tests/engine/hit-test/scope.test.ts
+++ b/tests/engine/hit-test/scope.test.ts
@@ -2,6 +2,8 @@ import { describe, expect, test } from 'bun:test'
 
 import { SceneGraph } from '@open-pencil/core'
 
+import { expectDefined, getNodeOrThrow } from '#tests/helpers/assert'
+
 function pageId(graph: SceneGraph) {
   return graph.getPages()[0].id
 }
@@ -31,21 +33,21 @@ describe('hitTest — group behavior', () => {
     const { graph, page } = setup()
     const hit = graph.hitTest(110, 110, page)
     expect(hit).not.toBeNull()
-    expect(hit!.type).toBe('GROUP')
+    expect(expectDefined(hit, 'hit node').type).toBe('GROUP')
   })
 
   test('hitTestDeep on child returns child directly', () => {
     const { graph, page, child } = setup()
     const hit = graph.hitTestDeep(110, 110, page)
     expect(hit).not.toBeNull()
-    expect(hit!.id).toBe(child.id)
+    expect(expectDefined(hit, 'hit node').id).toBe(child.id)
   })
 
   test('hitTest with scope=group returns child', () => {
     const { graph, group } = setup()
     const hit = graph.hitTest(110, 110, group.id)
     expect(hit).not.toBeNull()
-    expect(hit!.name).toBe('Rect')
+    expect(expectDefined(hit, 'hit node').name).toBe('Rect')
   })
 
   test('hitTest miss inside group returns null', () => {
@@ -93,28 +95,28 @@ describe('hitTest — nested groups', () => {
     const { graph, page } = setup()
     const hit = graph.hitTest(100, 100, page)
     expect(hit).not.toBeNull()
-    expect(hit!.name).toBe('GroupA')
+    expect(expectDefined(hit, 'hit node').name).toBe('GroupA')
   })
 
   test('click with scope=GroupA returns GroupB', () => {
     const { graph, groupA } = setup()
     const hit = graph.hitTest(150, 150, groupA.id)
     expect(hit).not.toBeNull()
-    expect(hit!.name).toBe('GroupB')
+    expect(expectDefined(hit, 'hit node').name).toBe('GroupB')
   })
 
   test('click with scope=GroupB returns DeepRect', () => {
     const { graph, groupB } = setup()
     const hit = graph.hitTest(160, 160, groupB.id)
     expect(hit).not.toBeNull()
-    expect(hit!.name).toBe('DeepRect')
+    expect(expectDefined(hit, 'hit node').name).toBe('DeepRect')
   })
 
   test('hitTestDeep from page returns deepest child', () => {
     const { graph, page, rect } = setup()
     const hit = graph.hitTestDeep(160, 160, page)
     expect(hit).not.toBeNull()
-    expect(hit!.id).toBe(rect.id)
+    expect(expectDefined(hit, 'hit node').id).toBe(rect.id)
   })
 })
 
@@ -140,7 +142,7 @@ describe('hitTest — locked nodes', () => {
 
     const hit = graph.hitTestDeep(10, 10, page)
     expect(hit).not.toBeNull()
-    expect(hit!.name).toBe('LockedFrame')
+    expect(expectDefined(hit, 'hit node').name).toBe('LockedFrame')
   })
 
   test('locked leaf node is still clickable', () => {
@@ -157,7 +159,7 @@ describe('hitTest — locked nodes', () => {
 
     const hit = graph.hitTest(25, 25, page)
     expect(hit).not.toBeNull()
-    expect(hit!.name).toBe('LockedRect')
+    expect(expectDefined(hit, 'hit node').name).toBe('LockedRect')
   })
 })
 
@@ -194,7 +196,7 @@ describe('scene graph — locked node operations', () => {
 
     const node = graph.getNode(rect.id)
     expect(node).not.toBeNull()
-    expect(node!.locked).toBe(true)
+    expect(expectDefined(node, 'node').locked).toBe(true)
   })
 
   test('lock can be toggled', () => {
@@ -208,11 +210,11 @@ describe('scene graph — locked node operations', () => {
       height: 50
     })
 
-    expect(graph.getNode(rect.id)!.locked).toBe(false)
+    expect(getNodeOrThrow(graph, rect.id).locked).toBe(false)
     graph.updateNode(rect.id, { locked: true })
-    expect(graph.getNode(rect.id)!.locked).toBe(true)
+    expect(getNodeOrThrow(graph, rect.id).locked).toBe(true)
     graph.updateNode(rect.id, { locked: false })
-    expect(graph.getNode(rect.id)!.locked).toBe(false)
+    expect(getNodeOrThrow(graph, rect.id).locked).toBe(false)
   })
 
   test('visibility can be toggled', () => {
@@ -226,11 +228,11 @@ describe('scene graph — locked node operations', () => {
       height: 50
     })
 
-    expect(graph.getNode(rect.id)!.visible).toBe(true)
+    expect(getNodeOrThrow(graph, rect.id).visible).toBe(true)
     graph.updateNode(rect.id, { visible: false })
-    expect(graph.getNode(rect.id)!.visible).toBe(false)
+    expect(getNodeOrThrow(graph, rect.id).visible).toBe(false)
     graph.updateNode(rect.id, { visible: true })
-    expect(graph.getNode(rect.id)!.visible).toBe(true)
+    expect(getNodeOrThrow(graph, rect.id).visible).toBe(true)
   })
 })
 
@@ -255,7 +257,7 @@ describe('hitTest — frame with children', () => {
 
     const hit = graph.hitTest(70, 70, frame.id)
     expect(hit).not.toBeNull()
-    expect(hit!.id).toBe(child.id)
+    expect(expectDefined(hit, 'hit node').id).toBe(child.id)
   })
 
   test('rotated frame scope hit test finds children using rotated local bounds', () => {
@@ -280,7 +282,7 @@ describe('hitTest — frame with children', () => {
     // point that is inside rotated frame bounds and child bounds
     const hitInside = graph.hitTest(193, 111, frame.id)
     expect(hitInside).not.toBeNull()
-    expect(hitInside!.id).toBe(child.id)
+    expect(expectDefined(hitInside, 'inside hit node').id).toBe(child.id)
 
     // point that would be inside if frame were not rotated
     const hitOutside = graph.hitTest(160, 130, frame.id)
@@ -309,7 +311,7 @@ describe('hitTest — opaque containers (COMPONENT/INSTANCE)', () => {
 
     const hit = graph.hitTest(10, 10, page)
     expect(hit).not.toBeNull()
-    expect(hit!.name).toBe('MyComp')
+    expect(expectDefined(hit, 'hit node').name).toBe('MyComp')
   })
 
   test('hitTestDeep inside COMPONENT scope finds child', () => {
@@ -332,7 +334,7 @@ describe('hitTest — opaque containers (COMPONENT/INSTANCE)', () => {
 
     const hit = graph.hitTestDeep(10, 10, comp.id)
     expect(hit).not.toBeNull()
-    expect(hit!.id).toBe(child.id)
+    expect(expectDefined(hit, 'hit node').id).toBe(child.id)
   })
 
   test('hitTest on INSTANCE returns instance itself', () => {
@@ -355,7 +357,7 @@ describe('hitTest — opaque containers (COMPONENT/INSTANCE)', () => {
 
     const hit = graph.hitTest(55, 55, page)
     expect(hit).not.toBeNull()
-    expect(hit!.name).toBe('MyInstance')
+    expect(expectDefined(hit, 'hit node').name).toBe('MyInstance')
   })
 
   test('hitTestDeep inside INSTANCE scope finds child', () => {
@@ -378,7 +380,7 @@ describe('hitTest — opaque containers (COMPONENT/INSTANCE)', () => {
 
     const hit = graph.hitTestDeep(55, 55, inst.id)
     expect(hit).not.toBeNull()
-    expect(hit!.id).toBe(child.id)
+    expect(expectDefined(hit, 'hit node').id).toBe(child.id)
   })
 })
 
@@ -410,7 +412,7 @@ describe('hitTest — absolute position and scope offset', () => {
 
     const hit = graph.hitTest(250, 360, frame.id)
     expect(hit).not.toBeNull()
-    expect(hit!.id).toBe(child.id)
+    expect(expectDefined(hit, 'hit node').id).toBe(child.id)
 
     const missHit = graph.hitTest(50, 60, frame.id)
     expect(missHit).toBeNull()
diff --git a/tests/engine/kiwi/serialize-fixes.test.ts b/tests/engine/kiwi/serialize-fixes.test.ts
index 3cd6d00ce..d0c5cbeb2 100644
--- a/tests/engine/kiwi/serialize-fixes.test.ts
+++ b/tests/engine/kiwi/serialize-fixes.test.ts
@@ -8,6 +8,8 @@ import {
   sceneNodeToKiwi
 } from '@open-pencil/core'
 
+import { expectDefined, getNodeOrThrow } from '#tests/helpers/assert'
+
 beforeAll(async () => {
   await initCodec()
 })
@@ -55,7 +57,7 @@ describe('Fix 1: auto-layout child transforms', () => {
     const blobs: Uint8Array[] = []
     // Serialize the parent — children are serialized recursively
     const changes = sceneNodeToKiwi(
-      graph.getNode(parent.id)!,
+      getNodeOrThrow(graph, parent.id),
       ROOT_GUID,
       0,
       { value: 100 },
@@ -64,7 +66,10 @@ describe('Fix 1: auto-layout child transforms', () => {
     ) as Record<string, unknown>[]
 
     // changes[0] = parent, changes[1] = child
-    const childNc = changes.find((nc) => nc.name === 'Child')!
+    const childNc = expectDefined(
+      changes.find((nc) => nc.name === 'Child'),
+      'child node change'
+    )
     expect(childNc).toBeDefined()
     expect(childNc.transform.m02).toBe(0)
     expect(childNc.transform.m12).toBe(0)
@@ -93,7 +98,7 @@ describe('Fix 1: auto-layout child transforms', () => {
 
     const blobs: Uint8Array[] = []
     const changes = sceneNodeToKiwi(
-      graph.getNode(parent.id)!,
+      getNodeOrThrow(graph, parent.id),
       ROOT_GUID,
       0,
       { value: 100 },
@@ -101,7 +106,10 @@ describe('Fix 1: auto-layout child transforms', () => {
       blobs
     ) as Record<string, unknown>[]
 
-    const absNc = changes.find((nc) => nc.name === 'AbsChild')!
+    const absNc = expectDefined(
+      changes.find((nc) => nc.name === 'AbsChild'),
+      'absolute child node change'
+    )
     expect(absNc).toBeDefined()
     expect(absNc.transform.m02).toBe(75)
     expect(absNc.transform.m12).toBe(120)
@@ -128,7 +136,7 @@ describe('Fix 1: auto-layout child transforms', () => {
 
     const blobs: Uint8Array[] = []
     const changes = sceneNodeToKiwi(
-      graph.getNode(parent.id)!,
+      getNodeOrThrow(graph, parent.id),
       ROOT_GUID,
       0,
       { value: 100 },
@@ -136,7 +144,10 @@ describe('Fix 1: auto-layout child transforms', () => {
       blobs
     ) as Record<string, unknown>[]
 
-    const childNc = changes.find((nc) => nc.name === 'Child')!
+    const childNc = expectDefined(
+      changes.find((nc) => nc.name === 'Child'),
+      'child node change'
+    )
     expect(childNc).toBeDefined()
     expect(childNc.transform.m02).toBe(30)
     expect(childNc.transform.m12).toBe(45)
@@ -164,7 +175,7 @@ describe('Fix 1: auto-layout child transforms', () => {
 
     const blobs: Uint8Array[] = []
     const changes = sceneNodeToKiwi(
-      graph.getNode(parent.id)!,
+      getNodeOrThrow(graph, parent.id),
       ROOT_GUID,
       0,
       { value: 100 },
@@ -172,7 +183,10 @@ describe('Fix 1: auto-layout child transforms', () => {
       blobs
     ) as Record<string, unknown>[]
 
-    const itemNc = changes.find((nc) => nc.name === 'Item')!
+    const itemNc = expectDefined(
+      changes.find((nc) => nc.name === 'Item'),
+      'item node change'
+    )
     expect(itemNc.transform.m02).toBe(0)
     expect(itemNc.transform.m12).toBe(0)
   })
@@ -241,7 +255,10 @@ describe('Fix 2: frameMaskDisabled is inverse of clipsContent', () => {
     const exported = await exportFigFile(graph)
     const reimported = await parseFigFile(exported.buffer as ArrayBuffer)
 
-    const frame = [...reimported.nodes.values()].find((n) => n.name === 'ClipFrame')!
+    const frame = expectDefined(
+      [...reimported.nodes.values()].find((n) => n.name === 'ClipFrame'),
+      'ClipFrame'
+    )
     expect(frame.clipsContent).toBe(true)
   })
 })
@@ -382,7 +399,10 @@ describe('Fix 4: text lineHeight serialization', () => {
     const exported = await exportFigFile(graph)
     const reimported = await parseFigFile(exported.buffer as ArrayBuffer)
 
-    const textNode = [...reimported.nodes.values()].find((n) => n.type === 'TEXT')!
+    const textNode = expectDefined(
+      [...reimported.nodes.values()].find((n) => n.type === 'TEXT'),
+      'text node'
+    )
     expect(textNode.lineHeight).toBe(28)
   })
 })
@@ -409,7 +429,10 @@ describe('Fix 5: font family normalization in derivedTextData', () => {
     const exported = await exportFigFile(graph)
     const reimported = await parseFigFile(exported.buffer as ArrayBuffer)
 
-    const textNode = [...reimported.nodes.values()].find((n) => n.type === 'TEXT')!
+    const textNode = expectDefined(
+      [...reimported.nodes.values()].find((n) => n.type === 'TEXT'),
+      'text node'
+    )
     expect(textNode.fontFamily).toBe('DM Sans')
   })
 
@@ -430,7 +453,10 @@ describe('Fix 5: font family normalization in derivedTextData', () => {
     const exported = await exportFigFile(graph)
     const reimported = await parseFigFile(exported.buffer as ArrayBuffer)
 
-    const textNode = [...reimported.nodes.values()].find((n) => n.type === 'TEXT')!
+    const textNode = expectDefined(
+      [...reimported.nodes.values()].find((n) => n.type === 'TEXT'),
+      'text node'
+    )
     expect(textNode.fontFamily).toBe('Roboto')
   })
 
@@ -451,7 +477,10 @@ describe('Fix 5: font family normalization in derivedTextData', () => {
     const exported = await exportFigFile(graph)
     const reimported = await parseFigFile(exported.buffer as ArrayBuffer)
 
-    const textNode = [...reimported.nodes.values()].find((n) => n.type === 'TEXT')!
+    const textNode = expectDefined(
+      [...reimported.nodes.values()].find((n) => n.type === 'TEXT'),
+      'text node'
+    )
     expect(textNode.fontFamily).toBe('Inter')
   })
 
@@ -533,7 +562,7 @@ describe('Integration: auto-layout component with all fixes', () => {
     // Verify kiwi output directly
     const blobs: Uint8Array[] = []
     const changes = sceneNodeToKiwi(
-      graph.getNode(card.id)!,
+      getNodeOrThrow(graph, card.id),
       ROOT_GUID,
       0,
       { value: 100 },
@@ -542,8 +571,14 @@ describe('Integration: auto-layout component with all fixes', () => {
     ) as Record<string, unknown>[]
 
     const cardNc = changes[0]
-    const titleNc = changes.find((nc) => nc.name === 'Title')!
-    const valueNc = changes.find((nc) => nc.name === 'Value')!
+    const titleNc = expectDefined(
+      changes.find((nc) => nc.name === 'Title'),
+      'Title node change'
+    )
+    const valueNc = expectDefined(
+      changes.find((nc) => nc.name === 'Value'),
+      'Value node change'
+    )
 
     // Fix 1: children have zero transforms
     expect(titleNc.transform.m02).toBe(0)
@@ -571,8 +606,14 @@ describe('Integration: auto-layout component with all fixes', () => {
     const reimported = await parseFigFile(exported.buffer as ArrayBuffer)
 
     const nodes = [...reimported.nodes.values()]
-    const cardNode = nodes.find((n) => n.name === 'StatCard')!
-    const titleNode = nodes.find((n) => n.name === 'Title')!
+    const cardNode = expectDefined(
+      nodes.find((n) => n.name === 'StatCard'),
+      'StatCard node'
+    )
+    const titleNode = expectDefined(
+      nodes.find((n) => n.name === 'Title'),
+      'Title node'
+    )
 
     expect(cardNode.layoutMode).toBe('VERTICAL')
     expect(cardNode.clipsContent).toBe(true)
diff --git a/tests/engine/layout/auto-layout.test.ts b/tests/engine/layout/auto-layout.test.ts
index 6725a2607..00836f47f 100644
--- a/tests/engine/layout/auto-layout.test.ts
+++ b/tests/engine/layout/auto-layout.test.ts
@@ -10,6 +10,7 @@ import {
 
 import { createEditorStore } from '@/app/editor/session'
 
+import { getNodeOrThrow } from '#tests/helpers/assert'
 import { autoFrame, loadFixtureGraph, pageId, rect } from '#tests/helpers/layout'
 
 describe('Auto Layout', () => {
@@ -394,7 +395,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.width).toBe(130)
     })
 
@@ -413,7 +414,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.height).toBe(110)
     })
 
@@ -433,7 +434,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.width).toBe(160)
       expect(f.height).toBe(90)
     })
@@ -591,7 +592,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.width).toBe(50)
       expect(f.height).toBe(30)
     })
@@ -616,7 +617,7 @@ describe('Auto Layout', () => {
       computeLayout(graph, outer.id)
 
       const children = graph.getChildren(outer.id)
-      const innerNode = graph.getNode(inner.id)!
+      const innerNode = getNodeOrThrow(graph, inner.id)
       expect(innerNode.width).toBe(50)
       expect(innerNode.height).toBe(50)
       expect(children[1].x).toBe(0)
@@ -663,7 +664,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, outer.id)
 
-      const innerNode = graph.getNode(inner.id)!
+      const innerNode = getNodeOrThrow(graph, inner.id)
       expect(innerNode.width).toBe(105)
       expect(innerNode.x).toBe(0)
 
@@ -692,7 +693,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, outer.id)
 
-      const innerNode = graph.getNode(inner.id)!
+      const innerNode = getNodeOrThrow(graph, inner.id)
       expect(innerNode.height).toBe(130)
 
       const outerChildren = graph.getChildren(outer.id)
@@ -723,7 +724,7 @@ describe('Auto Layout', () => {
 
       computeAllLayouts(graph)
 
-      const middleNode = graph.getNode(middle.id)!
+      const middleNode = getNodeOrThrow(graph, middle.id)
       expect(middleNode.width).toBe(105)
       expect(middleNode.height).toBe(30)
 
@@ -834,7 +835,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const c = graph.getNode(child.id)!
+      const c = getNodeOrThrow(graph, child.id)
       expect(c.x).toBe(100)
       expect(c.y).toBe(100)
     })
@@ -854,7 +855,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.width).toBe(60)
       expect(f.height).toBe(40)
     })
@@ -890,7 +891,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.width).toBe(10)
       expect(f.height).toBe(10)
     })
@@ -906,7 +907,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.width).toBe(50)
 
       const children = graph.getChildren(frame.id)
@@ -929,7 +930,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.width).toBe(400)
       expect(f.height).toBe(120)
     })
@@ -949,7 +950,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.height).toBe(110)
       expect(f.width).toBe(200)
     })
@@ -975,7 +976,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, outer.id)
 
-      const innerNode = graph.getNode(inner.id)!
+      const innerNode = getNodeOrThrow(graph, inner.id)
       // 400 - 100 - 10 = 290
       expect(innerNode.width).toBe(290)
     })
@@ -1155,9 +1156,9 @@ describe('Auto Layout', () => {
 
       setTextMeasurer(null)
 
-      const updatedText = graph.getNode(text.id)!
-      const updatedArrow1 = graph.getNode(arrow1.id)!
-      const updatedArrow2 = graph.getNode(arrow2.id)!
+      const updatedText = getNodeOrThrow(graph, text.id)
+      const updatedArrow1 = getNodeOrThrow(graph, arrow1.id)
+      const updatedArrow2 = getNodeOrThrow(graph, arrow2.id)
 
       expect(updatedText.width).toBe(60)
 
@@ -1320,7 +1321,7 @@ describe('Auto Layout', () => {
       computeAllLayouts(graph)
       setTextMeasurer(null)
 
-      const updatedText = graph.getNode(text.id)!
+      const updatedText = getNodeOrThrow(graph, text.id)
       // Should stretch to 300 - 20 - 20 = 260, NOT stay at 100
       expect(updatedText.width).toBe(260)
     })
@@ -1354,7 +1355,7 @@ describe('Auto Layout', () => {
       computeAllLayouts(graph)
       setTextMeasurer(null)
 
-      const updatedText = graph.getNode(text.id)!
+      const updatedText = getNodeOrThrow(graph, text.id)
       expect(updatedText.width).toBe(300)
       expect(updatedText.height).toBe(20)
     })
@@ -1395,7 +1396,7 @@ describe('Auto Layout', () => {
 
       // 400 - 100 - 10 = 290 available for the fill text
       expect(receivedWidths.length).toBeGreaterThan(0)
-      const updatedText = graph.getNode(text.id)!
+      const updatedText = getNodeOrThrow(graph, text.id)
       expect(updatedText.width).toBe(290)
     })
 
@@ -1429,7 +1430,7 @@ describe('Auto Layout', () => {
       setTextMeasurer(null)
 
       expect(measureCalled).toBe(false)
-      const updatedText = graph.getNode(text.id)!
+      const updatedText = getNodeOrThrow(graph, text.id)
       expect(updatedText.width).toBe(150)
       expect(updatedText.height).toBe(40)
     })
@@ -1512,7 +1513,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, outer.id)
 
-      const innerNode = graph.getNode(inner.id)!
+      const innerNode = getNodeOrThrow(graph, inner.id)
       expect(innerNode.width).toBe(250)
     })
   })
@@ -1711,17 +1712,17 @@ describe('Auto Layout', () => {
       const child = rect(graph, frame.id, 80, 60)
 
       computeLayout(graph, frame.id)
-      expect(graph.getNode(child.id)!.width).toBe(80)
+      expect(getNodeOrThrow(graph, child.id).width).toBe(80)
 
       graph.updateNode(child.id, { visible: false })
       computeLayout(graph, frame.id)
-      expect(graph.getNode(child.id)!.width).toBe(80)
-      expect(graph.getNode(child.id)!.height).toBe(60)
+      expect(getNodeOrThrow(graph, child.id).width).toBe(80)
+      expect(getNodeOrThrow(graph, child.id).height).toBe(60)
 
       graph.updateNode(child.id, { visible: true })
       computeLayout(graph, frame.id)
-      expect(graph.getNode(child.id)!.width).toBe(80)
-      expect(graph.getNode(child.id)!.height).toBe(60)
+      expect(getNodeOrThrow(graph, child.id).width).toBe(80)
+      expect(getNodeOrThrow(graph, child.id).height).toBe(60)
     })
   })
 
@@ -1740,7 +1741,7 @@ describe('Auto Layout', () => {
 
       computeLayout(graph, frame.id)
 
-      const f = graph.getNode(frame.id)!
+      const f = getNodeOrThrow(graph, frame.id)
       expect(f.width).toBe(100)
 
       const children = graph.getChildren(frame.id)
diff --git a/tests/engine/render/canvas/silhouette-autopsy.test.ts b/tests/engine/render/canvas/silhouette-autopsy.test.ts
index e753956fe..097120a84 100644
--- a/tests/engine/render/canvas/silhouette-autopsy.test.ts
+++ b/tests/engine/render/canvas/silhouette-autopsy.test.ts
@@ -19,6 +19,7 @@ import { SkiaRenderer } from '#core/canvas'
 import { SceneGraph } from '#core/scene-graph'
 import { fontManager } from '#core/text'
 
+import { expectDefined } from '#tests/helpers/assert'
 import { coreSourcePath, publicPath, testPath as repoTestPath } from '#tests/helpers/paths'
 
 // === CLAIM EXTRACTION ===
@@ -75,7 +76,7 @@ describe('Doc 01 — The Current Engine: Static Code Claims', () => {
     // Use a targeted search near the Effect interface definition
     const effectInterfaceMatch = src.match(/interface Effect\s*\{([^}]+)\}/)
     expect(effectInterfaceMatch).toBeTruthy()
-    const effectBody = effectInterfaceMatch![1]
+    const effectBody = expectDefined(effectInterfaceMatch, 'effectInterfaceMatch')[1]
     for (const type of [
       'DROP_SHADOW',
       'INNER_SHADOW',
@@ -107,7 +108,7 @@ describe('Doc 01 — The Current Engine: Static Code Claims', () => {
       /export function renderShapeUncached[\s\S]*?(?=\nexport function|\n$)/
     )
     expect(renderShapeUncachedMatch).toBeTruthy()
-    const body = renderShapeUncachedMatch![0]
+    const body = expectDefined(renderShapeUncachedMatch, 'renderShapeUncachedMatch')[0]
 
     // Find indices of key calls
     const behindIdx = body.indexOf("'behind'")
@@ -132,7 +133,7 @@ describe('Doc 01 — The Current Engine: Static Code Claims', () => {
       /export function renderNode[\s\S]*?(?=\nexport function|\nexport const)/
     )
     expect(renderNodeMatch).toBeTruthy()
-    const body = renderNodeMatch![0]
+    const body = expectDefined(renderNodeMatch, 'renderNodeMatch')[0]
 
     // Verify opacity saveLayer comes before layerBlur saveLayer
     const opacityLayerIdx = body.indexOf('opacity < 1')
@@ -170,7 +171,7 @@ describe('Doc 01 — The Current Engine: Static Code Claims', () => {
       /function drawTextInnerShadow[\s\S]*?(?=\nfunction |\nexport )/
     )
     expect(drawTextInnerShadowMatch).toBeTruthy()
-    const body = drawTextInnerShadowMatch![0]
+    const body = expectDefined(drawTextInnerShadowMatch, 'drawTextInnerShadowMatch')[0]
 
     // Count saveLayer calls — there are 4 (Master, Restrictive, Blur, DstOut)
     // plus 2 canvas.save() calls (child transform + offset transform)
@@ -199,7 +200,7 @@ describe('Doc 01 — The Current Engine: Static Code Claims', () => {
       /export function renderShape[\s\S]*?(?=\nexport function|\nexport const)/
     )
     expect(renderShapeMatch).toBeTruthy()
-    const body = renderShapeMatch![0]
+    const body = expectDefined(renderShapeMatch, 'renderShapeMatch')[0]
     expect(body).toContain('nodePictureCache')
     expect(body).toContain('PictureRecorder')
   })
@@ -213,7 +214,7 @@ describe('Doc 01 — The Current Engine: Static Code Claims', () => {
       /function getShadowShapeChild[\s\S]*?(?=\nfunction |\nexport )/
     )
     expect(getShadowShapeChildFn).toBeTruthy()
-    const body = getShadowShapeChildFn![0]
+    const body = expectDefined(getShadowShapeChildFn, 'getShadowShapeChildFn')[0]
     // No for loop over children
     expect(body).not.toMatch(/for\s*\(.*childIds/)
     // Accesses childIds twice: once for .length guard, once for [0] read
@@ -243,7 +244,7 @@ describe('Doc 02 — Formula Deconstruction: Static Code Claims', () => {
       /function drawTextInnerShadow[\s\S]*?(?=\nfunction |\nexport )/
     )
     expect(drawTextInnerShadowMatch).toBeTruthy()
-    const body = drawTextInnerShadowMatch![0]
+    const body = expectDefined(drawTextInnerShadowMatch, 'drawTextInnerShadowMatch')[0]
 
     // 4 saveLayer: Master, Restrictive, Blur, DstOut
     // 2 save: child transform, offset transform
@@ -303,7 +304,7 @@ describe('Doc 03 — Artifact Analysis: Static + Runtime Verification', () => {
       /function drawTextInnerShadow[\s\S]*?(?=\nfunction |\nexport )/
     )
     expect(drawTextInnerShadowMatch).toBeTruthy()
-    const body = drawTextInnerShadowMatch![0]
+    const body = expectDefined(drawTextInnerShadowMatch, 'drawTextInnerShadowMatch')[0]
 
     // Check the expand calculation
     expect(body).toContain('const expand')
@@ -316,7 +317,7 @@ describe('Doc 03 — Artifact Analysis: Static + Runtime Verification', () => {
     const src = readSource(scenePath)
     const match = src.match(/function getShadowShapeChild[\s\S]*?(?=\nfunction |\nexport )/)
     expect(match).toBeTruthy()
-    const body = match![0]
+    const body = expectDefined(match, 'match')[0]
     // Verify it returns early after first child
     expect(body).toContain('return child')
     // Verify no array accumulation
@@ -354,7 +355,7 @@ describe('Doc 01/03 — Runtime Behavior Verification', () => {
       void fontPath
     }
 
-    const surface = ck.MakeSurface(200, 200)!
+    const surface = expectDefined(ck.MakeSurface(200, 200), 'CanvasKit surface')
     renderer = new SkiaRenderer(ck, surface)
     renderer.fontProvider = fontProvider
     renderer.fontsLoaded = true
@@ -516,7 +517,7 @@ describe('Doc 01/03 — Runtime Behavior Verification', () => {
       /function drawTextInnerShadow[\s\S]*?(?=\nfunction |\nexport )/
     )
     expect(drawTextInnerShadowMatch).toBeTruthy()
-    const body = drawTextInnerShadowMatch![0]
+    const body = expectDefined(drawTextInnerShadowMatch, 'drawTextInnerShadowMatch')[0]
 
     // MakeBlend IS called (for tintFilter and solidBlackFilter)
     expect(body).toContain('MakeBlend')
@@ -543,7 +544,7 @@ describe('Doc 01 — LAYER_BLUR Round-Trip Loss Verification', () => {
     const src = readSource(schemaPath)
     const effectTypeBlock = src.match(/enum EffectType\s*\{([^}]*)\}/)
     expect(effectTypeBlock).toBeTruthy()
-    const body = effectTypeBlock![1]
+    const body = expectDefined(effectTypeBlock, 'effectTypeBlock')[1]
     // Count the values (each is "NAME = N;")
     const valueCount = (body.match(/=\s*\d+\s*;/g) || []).length
     expect(valueCount).toBe(4)
@@ -576,7 +577,7 @@ describe('Doc 02/03 — Cache Infrastructure Verification', () => {
     const rendererSrc = readSource(rendererPath)
     const destroyMatch = rendererSrc.match(/destroy\(\)[\s\S]*?(?=\n  \w|\n\})/)
     expect(destroyMatch).toBeTruthy()
-    const body = destroyMatch![0]
+    const body = expectDefined(destroyMatch, 'destroyMatch')[0]
     // destroy() delegates to destroyRenderer — verify the lifecycle module cleans caches
     expect(body).toContain('destroyRenderer')
     const lifecycleSrc = readSource(lifecyclePath)
diff --git a/tests/engine/scene-graph/basic.test.ts b/tests/engine/scene-graph/basic.test.ts
index ecc15404f..217c15351 100644
--- a/tests/engine/scene-graph/basic.test.ts
+++ b/tests/engine/scene-graph/basic.test.ts
@@ -2,6 +2,8 @@ import { describe, expect, test } from 'bun:test'
 
 import { SceneGraph } from '@open-pencil/core'
 
+import { expectDefined } from '#tests/helpers/assert'
+
 function pageId(graph: SceneGraph) {
   return graph.getPages()[0].id
 }
@@ -16,7 +18,7 @@ describe('SceneGraph', () => {
     const id = rect(graph, 'Rect', 100, 100, 200, 150)
     const node = graph.getNode(id)
     expect(node).toBeDefined()
-    expect(node!.type).toBe('RECTANGLE')
+    expect(expectDefined(node, 'node').type).toBe('RECTANGLE')
     expect(node.x).toBe(100)
     expect(node.width).toBe(200)
   })
@@ -146,13 +148,13 @@ describe('SceneGraph', () => {
     const r = rect(graph, 'R', 100, 200)
     const node = graph.getNode(r)
     expect(node).toBeDefined()
-    expect(node!.parentId).toBe(page)
+    expect(expectDefined(node, 'node').parentId).toBe(page)
     graph.reparentNode(r, page)
     // Position should not change
     const after = graph.getNode(r)
     expect(after).toBeDefined()
-    expect(after!.x).toBe(100)
-    expect(after!.y).toBe(200)
+    expect(expectDefined(after, 'updated node').x).toBe(100)
+    expect(expectDefined(after, 'updated node').y).toBe(200)
     expect(after.parentId).toBe(page)
     expect(graph.getChildren(page)).toHaveLength(1)
   })
@@ -176,7 +178,7 @@ describe('SceneGraph', () => {
     // Now node is inside frame at (200,100), so local coords should be (100, 50)
     const after = graph.getNode(r)
     expect(after).toBeDefined()
-    expect(after!.x).toBe(100)
+    expect(expectDefined(after, 'updated node').x).toBe(100)
     expect(after.y).toBe(50)
     // Absolute position preserved
     const absAfter = graph.getAbsolutePosition(r)
@@ -245,7 +247,7 @@ describe('SceneGraph', () => {
     // Inner was at (100,100), frame is at (50,50), so inner's local = (50,50)
     const innerNode = graph.getNode(inner)
     expect(innerNode).toBeDefined()
-    expect(innerNode!.x).toBe(50)
+    expect(expectDefined(innerNode, 'inner node').x).toBe(50)
     expect(innerNode.y).toBe(50)
     // Child still at (10,10) relative to inner, absolute = (110,110)
     expect(graph.getAbsolutePosition(child)).toEqual({ x: 110, y: 110 })
@@ -326,7 +328,7 @@ describe('SceneGraph', () => {
     graph.updateNode(id, { x: 200, name: 'Updated' })
     const node = graph.getNode(id)
     expect(node).toBeDefined()
-    expect(node!.x).toBe(200)
+    expect(expectDefined(node, 'node').x).toBe(200)
     expect(node.name).toBe('Updated')
   })
 
@@ -340,7 +342,7 @@ describe('SceneGraph', () => {
     const child = graph.createNode('RECTANGLE', comp.id, { name: 'BG', width: 100, height: 40 })
     const instance = graph.createInstance(comp.id, pageId(graph))
     expect(instance).toBeDefined()
-    expect(instance!.type).toBe('INSTANCE')
+    expect(expectDefined(instance, 'instance').type).toBe('INSTANCE')
     expect(instance.componentId).toBe(comp.id)
     const instChildren = graph.getChildren(instance.id)
     expect(instChildren).toHaveLength(1)
@@ -358,7 +360,7 @@ describe('SceneGraph', () => {
     const label = graph.createNode('TEXT', comp.id, { name: 'Title', text: 'Hello', fontSize: 14 })
     const instance = graph.createInstance(comp.id, pageId(graph))
     expect(instance).toBeDefined()
-    const instLabel = graph.getChildren(instance!.id)[0]
+    const instLabel = graph.getChildren(expectDefined(instance, 'instance').id)[0]
     expect(instLabel.text).toBe('Hello')
 
     graph.updateNode(label.id, { text: 'Updated', fontSize: 18 })
@@ -378,7 +380,7 @@ describe('SceneGraph', () => {
     graph.createNode('TEXT', comp.id, { name: 'Title', text: 'Default', fontSize: 14 })
     const instance = graph.createInstance(comp.id, pageId(graph))
     expect(instance).toBeDefined()
-    const instLabel = graph.getChildren(instance!.id)[0]
+    const instLabel = graph.getChildren(expectDefined(instance, 'instance').id)[0]
 
     // Override the text on the instance child
     graph.updateNode(instLabel.id, { text: 'Custom' })
@@ -403,12 +405,12 @@ describe('SceneGraph', () => {
     graph.createNode('RECTANGLE', comp.id, { name: 'BG' })
     const instance = graph.createInstance(comp.id, pageId(graph))
     expect(instance).toBeDefined()
-    expect(graph.getChildren(instance!.id)).toHaveLength(1)
+    expect(graph.getChildren(expectDefined(instance, 'instance').id)).toHaveLength(1)
 
     graph.createNode('TEXT', comp.id, { name: 'Label', text: 'New' })
     graph.syncInstances(comp.id)
 
-    const instChildren = graph.getChildren(instance!.id)
+    const instChildren = graph.getChildren(expectDefined(instance, 'instance').id)
     expect(instChildren).toHaveLength(2)
     expect(instChildren[1].name).toBe('Label')
     expect(instChildren[1].text).toBe('New')
@@ -424,10 +426,10 @@ describe('SceneGraph', () => {
     graph.createNode('RECTANGLE', comp.id, { name: 'BG' })
     const instance = graph.createInstance(comp.id, pageId(graph))
     expect(instance).toBeDefined()
-    expect(instance!.type).toBe('INSTANCE')
+    expect(expectDefined(instance, 'instance').type).toBe('INSTANCE')
 
-    graph.detachInstance(instance!.id)
-    expect(instance!.type).toBe('FRAME')
+    graph.detachInstance(expectDefined(instance, 'instance').id)
+    expect(expectDefined(instance, 'instance').type).toBe('FRAME')
     expect(instance.componentId).toBeNull()
     expect(graph.getInstances(comp.id)).toHaveLength(0)
   })
@@ -1019,13 +1021,13 @@ describe('updateNode', () => {
     expect(textNode).toBeDefined()
     // Simulate a cached textPicture
     const fakePicture = new Uint8Array([1, 2, 3])
-    textNode!.textPicture = fakePicture
+    expectDefined(textNode, 'text node').textPicture = fakePicture
 
     // Changing fontSize (a TEXT_PICTURE_KEY) should null the cache
     graph.updateNode(textId, { fontSize: 24 })
     const afterUpdate = graph.getNode(textId)
     expect(afterUpdate).toBeDefined()
-    expect(afterUpdate!.textPicture).toBeNull()
+    expect(expectDefined(afterUpdate, 'updated node').textPicture).toBeNull()
   })
 
   test('textPicture survives non-text property change on TEXT node', () => {
@@ -1041,13 +1043,13 @@ describe('updateNode', () => {
     const fakePicture = new Uint8Array([4, 5, 6])
     const textNode = graph.getNode(textId)
     expect(textNode).toBeDefined()
-    textNode!.textPicture = fakePicture
+    expectDefined(textNode, 'text node').textPicture = fakePicture
 
     // Changing opacity (NOT a TEXT_PICTURE_KEY) should preserve textPicture
     graph.updateNode(textId, { opacity: 0.5 })
     const afterUpdate = graph.getNode(textId)
     expect(afterUpdate).toBeDefined()
-    expect(afterUpdate!.textPicture).toBe(fakePicture)
+    expect(expectDefined(afterUpdate, 'updated node').textPicture).toBe(fakePicture)
   })
 
   test('textPicture is nulled when textPicture is already null', () => {
@@ -1064,7 +1066,7 @@ describe('updateNode', () => {
     graph.updateNode(textId, { fontSize: 16 })
     const afterUpdate = graph.getNode(textId)
     expect(afterUpdate).toBeDefined()
-    expect(afterUpdate!.textPicture).toBeNull()
+    expect(expectDefined(afterUpdate, 'updated node').textPicture).toBeNull()
   })
 })
 
diff --git a/tests/engine/svg/export.test.ts b/tests/engine/svg/export.test.ts
index bdb7707df..d68c328ce 100644
--- a/tests/engine/svg/export.test.ts
+++ b/tests/engine/svg/export.test.ts
@@ -9,6 +9,8 @@ import {
   vectorNetworkToSVGPaths
 } from '@open-pencil/core'
 
+import { expectDefined } from '#tests/helpers/assert'
+
 function makeGraph() {
   const graph = new SceneGraph()
   graph.createNode('CANVAS', graph.rootId, { name: 'Page 1' })
@@ -23,6 +25,19 @@ function exportSVG(graph: SceneGraph, nodeIds: string[], xmlDecl = false): strin
   return renderNodesToSVG(graph, pageId(graph), nodeIds, { xmlDeclaration: xmlDecl })
 }
 
+function exportSVGOrThrow(graph: SceneGraph, nodeIds: string[], xmlDecl = false): string {
+  return expectDefined(exportSVG(graph, nodeIds, xmlDecl), 'SVG output')
+}
+
+function renderNodesToSVGOrThrow(
+  graph: SceneGraph,
+  pageId: string,
+  nodeIds: string[],
+  options: Parameters<typeof renderNodesToSVG>[3]
+): string {
+  return expectDefined(renderNodesToSVG(graph, pageId, nodeIds, options), 'SVG output')
+}
+
 // --- SVGNode builder tests ---
 
 describe('svg() and renderSVGNode()', () => {
@@ -210,7 +225,7 @@ describe('renderNodesToSVG()', () => {
       height: 50,
       fills: [{ type: 'SOLID', color: { r: 1, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<svg')
     expect(result).toContain('width="100"')
     expect(result).toContain('height="50"')
@@ -226,10 +241,12 @@ describe('renderNodesToSVG()', () => {
       height: 10,
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const withDecl = renderNodesToSVG(graph, pageId(graph), [node.id], { xmlDeclaration: true })!
-    const withoutDecl = renderNodesToSVG(graph, pageId(graph), [node.id], {
+    const withDecl = renderNodesToSVGOrThrow(graph, pageId(graph), [node.id], {
+      xmlDeclaration: true
+    })
+    const withoutDecl = renderNodesToSVGOrThrow(graph, pageId(graph), [node.id], {
       xmlDeclaration: false
-    })!
+    })
     expect(withDecl).toStartWith('<?xml')
     expect(withoutDecl).toStartWith('<svg')
   })
@@ -241,7 +258,7 @@ describe('renderNodesToSVG()', () => {
       height: 60,
       fills: [{ type: 'SOLID', color: { r: 0, g: 0.5, b: 1, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<ellipse')
     expect(result).toContain('cx="40"')
     expect(result).toContain('cy="30"')
@@ -264,7 +281,7 @@ describe('renderNodesToSVG()', () => {
         }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<line')
     expect(result).toContain('x2="100"')
     expect(result).toContain('stroke-width="2"')
@@ -279,7 +296,7 @@ describe('renderNodesToSVG()', () => {
       starInnerRadius: 0.382,
       fills: [{ type: 'SOLID', color: { r: 1, g: 1, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<polygon')
     expect(result).toContain('points="')
   })
@@ -292,7 +309,7 @@ describe('renderNodesToSVG()', () => {
       pointCount: 6,
       fills: [{ type: 'SOLID', color: { r: 0, g: 1, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<polygon')
   })
 
@@ -304,7 +321,7 @@ describe('renderNodesToSVG()', () => {
       cornerRadius: 16,
       fills: [{ type: 'SOLID', color: { r: 1, g: 1, b: 1, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('rx="16"')
     expect(result).toContain('ry="16"')
   })
@@ -322,7 +339,7 @@ describe('renderNodesToSVG()', () => {
       bottomLeftRadius: 5,
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<path')
     expect(result).toContain('d="M10 0')
   })
@@ -338,7 +355,7 @@ describe('renderNodesToSVG()', () => {
       fontFamily: 'Inter',
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<text')
     expect(result).toContain('font-size="18"')
     expect(result).toContain('font-weight="700"')
@@ -357,7 +374,7 @@ describe('renderNodesToSVG()', () => {
       textAlignHorizontal: 'LEFT',
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('direction="rtl"')
     expect(result).toContain('text-anchor="end"')
     expect(result).toContain('x="180"')
@@ -377,7 +394,7 @@ describe('renderNodesToSVG()', () => {
         { start: 6, length: 4, style: { fontWeight: 700 } }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<tspan')
     expect(result).toContain('font-weight="700"')
   })
@@ -390,7 +407,7 @@ describe('renderNodesToSVG()', () => {
       opacity: 0.5,
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('opacity="0.5"')
   })
 
@@ -402,7 +419,7 @@ describe('renderNodesToSVG()', () => {
       rotation: 45,
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('rotate(45,')
   })
 
@@ -422,7 +439,7 @@ describe('renderNodesToSVG()', () => {
         }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('stroke-dasharray="5 3"')
   })
 
@@ -443,7 +460,7 @@ describe('renderNodesToSVG()', () => {
         }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('stroke-linecap="round"')
     expect(result).toContain('stroke-linejoin="bevel"')
   })
@@ -463,7 +480,7 @@ describe('renderNodesToSVG()', () => {
       y: 10,
       fills: [{ type: 'SOLID', color: { r: 0.9, g: 0.9, b: 0.9, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [frame.id])!
+    const result = exportSVGOrThrow(graph, [frame.id])
     expect(result).toContain('<g')
     expect(result).toContain('translate(10, 10)')
   })
@@ -481,7 +498,7 @@ describe('renderNodesToSVG()', () => {
       height: 200,
       fills: [{ type: 'SOLID', color: { r: 1, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [frame.id])!
+    const result = exportSVGOrThrow(graph, [frame.id])
     expect(result).toContain('<clipPath')
     expect(result).toContain('clip-path="url(#clip')
   })
@@ -505,7 +522,7 @@ describe('renderNodesToSVG()', () => {
       visible: false,
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 1, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [frame.id])!
+    const result = exportSVGOrThrow(graph, [frame.id])
     expect(result).toContain('fill="#FF0000"')
     expect(result).not.toContain('fill="#0000FF"')
   })
@@ -529,7 +546,7 @@ describe('renderNodesToSVG()', () => {
         }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<linearGradient')
     expect(result).toContain('<stop')
     expect(result).toContain('url(#grad')
@@ -554,7 +571,7 @@ describe('renderNodesToSVG()', () => {
         }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<radialGradient')
     expect(result).toContain('url(#grad')
   })
@@ -576,7 +593,7 @@ describe('renderNodesToSVG()', () => {
         }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<filter')
     expect(result).toContain('<feDropShadow')
     expect(result).toContain('dy="4"')
@@ -600,7 +617,7 @@ describe('renderNodesToSVG()', () => {
         }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<feGaussianBlur')
     expect(result).toContain('stdDeviation="5"')
   })
@@ -621,7 +638,7 @@ describe('renderNodesToSVG()', () => {
       height: 40,
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 1, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [a.id, b.id])!
+    const result = exportSVGOrThrow(graph, [a.id, b.id])
     expect(result).toContain('viewBox="0 0 100 50"')
     expect(result).toContain('<rect')
     expect(result).toContain('<ellipse')
@@ -635,7 +652,7 @@ describe('renderNodesToSVG()', () => {
       blendMode: 'MULTIPLY',
       fills: [{ type: 'SOLID', color: { r: 1, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('mix-blend-mode: multiply')
   })
 
@@ -646,7 +663,7 @@ describe('renderNodesToSVG()', () => {
       height: 50,
       fills: [{ type: 'SOLID', color: { r: 1, g: 0, b: 0, a: 1 }, opacity: 0.5, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('fill="#FF0000')
   })
 
@@ -664,7 +681,7 @@ describe('renderNodesToSVG()', () => {
       y: 10,
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [comp.id])!
+    const result = exportSVGOrThrow(graph, [comp.id])
     expect(result).toContain('<rect')
     expect(result).toContain('translate(10, 10)')
   })
@@ -678,7 +695,7 @@ describe('renderNodesToSVG()', () => {
         { type: 'SOLID', color: { r: 0.95, g: 0.95, b: 0.95, a: 1 }, opacity: 1, visible: true }
       ]
     })
-    const result = exportSVG(graph, [section.id])!
+    const result = exportSVGOrThrow(graph, [section.id])
     expect(result).toContain('<rect')
     expect(result).toContain('width="500"')
   })
@@ -691,7 +708,7 @@ describe('renderNodesToSVG()', () => {
       flipX: true,
       fills: [{ type: 'SOLID', color: { r: 0, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('scale(-1, 1)')
   })
 
@@ -710,7 +727,7 @@ describe('renderNodesToSVG()', () => {
         }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('stroke-opacity="0.5"')
   })
 
@@ -735,7 +752,7 @@ describe('renderNodesToSVG()', () => {
       height: 50,
       fills: [{ type: 'SOLID', color: { r: 1, g: 0, b: 0, a: 1 }, opacity: 1, visible: true }]
     })
-    const result = exportSVG(graph, [group.id])!
+    const result = exportSVGOrThrow(graph, [group.id])
     expect(result).toContain('<rect')
     expect(result).toContain('fill="#FF0000"')
   })
@@ -757,7 +774,7 @@ describe('renderNodesToSVG()', () => {
         }
       ]
     })
-    const result = exportSVG(graph, [node.id])!
+    const result = exportSVGOrThrow(graph, [node.id])
     expect(result).toContain('<filter')
     expect(result).toContain('<feGaussianBlur')
     expect(result).toContain('<feComposite')
diff --git a/tests/engine/text/editor.test.ts b/tests/engine/text/editor.test.ts
index ec661721a..e0602ed06 100644
--- a/tests/engine/text/editor.test.ts
+++ b/tests/engine/text/editor.test.ts
@@ -4,6 +4,8 @@ import type { CanvasKit } from 'canvaskit-wasm'
 
 import { TextEditor, type SceneNode } from '@open-pencil/core'
 
+import { expectDefined } from '#tests/helpers/assert'
+
 const mockCk = {} as CanvasKit
 
 function createEditor(text = 'Hello World') {
@@ -13,6 +15,10 @@ function createEditor(text = 'Hello World') {
   return { editor, node }
 }
 
+function editorState(editor: TextEditor) {
+  return expectDefined(editor.state, 'text editor state')
+}
+
 describe('TextEditor', () => {
   test('start initializes state', () => {
     const { editor } = createEditor()
@@ -45,15 +51,15 @@ describe('TextEditor', () => {
 
   test('insert at cursor position', () => {
     const { editor, node } = createEditor()
-    editor.state!.cursor = 5
+    editorState(editor).cursor = 5
     editor.insert(' Beautiful', node)
     expect(editor.state?.text).toBe('Hello Beautiful World')
   })
 
   test('insert replaces selection', () => {
     const { editor, node } = createEditor()
-    editor.state!.selectionAnchor = 0
-    editor.state!.cursor = 5
+    editorState(editor).selectionAnchor = 0
+    editorState(editor).cursor = 5
     editor.insert('Goodbye', node)
     expect(editor.state?.text).toBe('Goodbye World')
     expect(editor.state?.cursor).toBe(7)
@@ -69,15 +75,15 @@ describe('TextEditor', () => {
 
   test('backspace at start does nothing', () => {
     const { editor, node } = createEditor()
-    editor.state!.cursor = 0
+    editorState(editor).cursor = 0
     editor.backspace(node)
     expect(editor.state?.text).toBe('Hello World')
   })
 
   test('backspace deletes selection', () => {
     const { editor, node } = createEditor()
-    editor.state!.selectionAnchor = 6
-    editor.state!.cursor = 11
+    editorState(editor).selectionAnchor = 6
+    editorState(editor).cursor = 11
     editor.backspace(node)
     expect(editor.state?.text).toBe('Hello ')
     expect(editor.state?.cursor).toBe(6)
@@ -85,7 +91,7 @@ describe('TextEditor', () => {
 
   test('delete removes char after cursor', () => {
     const { editor, node } = createEditor()
-    editor.state!.cursor = 0
+    editorState(editor).cursor = 0
     editor.delete(node)
     expect(editor.state?.text).toBe('ello World')
     expect(editor.state?.cursor).toBe(0)
@@ -99,8 +105,8 @@ describe('TextEditor', () => {
 
   test('delete removes selection', () => {
     const { editor, node } = createEditor()
-    editor.state!.selectionAnchor = 0
-    editor.state!.cursor = 5
+    editorState(editor).selectionAnchor = 0
+    editorState(editor).cursor = 5
     editor.delete(node)
     expect(editor.state?.text).toBe(' World')
   })
@@ -119,8 +125,8 @@ describe('TextEditor', () => {
 
   test('moveLeft collapses selection to start', () => {
     const { editor } = createEditor()
-    editor.state!.selectionAnchor = 3
-    editor.state!.cursor = 8
+    editorState(editor).selectionAnchor = 3
+    editorState(editor).cursor = 8
     editor.moveLeft()
     expect(editor.state?.cursor).toBe(3)
     expect(editor.state?.selectionAnchor).toBeNull()
@@ -128,8 +134,8 @@ describe('TextEditor', () => {
 
   test('moveRight collapses selection to end', () => {
     const { editor } = createEditor()
-    editor.state!.selectionAnchor = 3
-    editor.state!.cursor = 8
+    editorState(editor).selectionAnchor = 3
+    editorState(editor).cursor = 8
     editor.moveRight()
     expect(editor.state?.cursor).toBe(8)
     expect(editor.state?.selectionAnchor).toBeNull()
@@ -145,28 +151,28 @@ describe('TextEditor', () => {
   test('hasSelection', () => {
     const { editor } = createEditor()
     expect(editor.hasSelection()).toBe(false)
-    editor.state!.selectionAnchor = 0
+    editorState(editor).selectionAnchor = 0
     expect(editor.hasSelection()).toBe(true)
   })
 
   test('hasSelection false when anchor equals cursor', () => {
     const { editor } = createEditor()
-    editor.state!.selectionAnchor = editor.state!.cursor
+    editorState(editor).selectionAnchor = editorState(editor).cursor
     expect(editor.hasSelection()).toBe(false)
   })
 
   test('getSelectionRange', () => {
     const { editor } = createEditor()
     expect(editor.getSelectionRange()).toBeNull()
-    editor.state!.selectionAnchor = 8
-    editor.state!.cursor = 3
+    editorState(editor).selectionAnchor = 8
+    editorState(editor).cursor = 3
     expect(editor.getSelectionRange()).toEqual([3, 8])
   })
 
   test('getSelectedText', () => {
     const { editor } = createEditor()
-    editor.state!.selectionAnchor = 0
-    editor.state!.cursor = 5
+    editorState(editor).selectionAnchor = 0
+    editorState(editor).cursor = 5
     expect(editor.getSelectedText()).toBe('Hello')
   })
 
@@ -192,14 +198,14 @@ describe('TextEditor', () => {
 
   test('moveWordRight from start', () => {
     const { editor } = createEditor()
-    editor.state!.cursor = 0
+    editorState(editor).cursor = 0
     editor.moveWordRight()
     expect(editor.state?.cursor).toBe(6)
   })
 
   test('moveLeft with extend creates selection', () => {
     const { editor } = createEditor()
-    editor.state!.cursor = 5
+    editorState(editor).cursor = 5
     editor.moveLeft(true)
     expect(editor.state?.selectionAnchor).toBe(5)
     expect(editor.state?.cursor).toBe(4)