diff --git a/frontend/e2e/settings-extensions.spec.ts b/frontend/e2e/settings-extensions.spec.ts
index 0f10644f..d334dcee 100644
--- a/frontend/e2e/settings-extensions.spec.ts
+++ b/frontend/e2e/settings-extensions.spec.ts
@@ -4,12 +4,25 @@ import { clickAtlasTrayTool } from './fixtures/atlasTray'
 import { deleteViaContextMenu, shapeDrawPoints, shapeObjects } from './fixtures/atlasShapeTool'
 import { paletteDialog } from './fixtures/palette'
 
-// Settings > Extensions (goal 0237 S2): a registry-derived list of
-// every canvas tool, each toggleable off. Shared pool: the only global
-// state this spec writes (Shape's own disabled flag) is restored to
-// its default (enabled) before the file ends, same cleanup discipline
-// display-density.spec.ts already establishes for a Settings toggle in
-// the shared pool; every board object created here is deleted here.
+// Settings > Extensions (goal 0237 S2, extended by goal 0237 S3's
+// rider): a registry-derived list of every registered canvas NOUN --
+// every tray tool plus every tool-less noun (diagram, sheet -- native
+// file-drop only, no tray button), each toggleable off. Shared pool:
+// the only global state this spec writes (Shape's own disabled flag)
+// is restored to its default (enabled) before the file ends, same
+// cleanup discipline display-density.spec.ts already establishes for a
+// Settings toggle in the shared pool; every board object created here
+// is deleted here.
+//
+// Disabling diagram/sheet gates useAtlasNativeFileDrop.ts's own drop
+// routing (a disabled drop falls through to the plain-card path). The
+// OS drop GESTURE itself is a structural e2e gap (testing.md's own
+// manual-only registry: WindowFilesDropped needs a real
+// *WebviewWindow, which server-mode Playwright's connection is not),
+// so the routing DECISION is proven at the honest layer instead --
+// useAtlasNativeFileDrop.test.ts's resolveFileDropKind Vitest suite --
+// and this spec only proves the row/toggle exists and states its
+// narrower scope.
 
 async function openExtensionsSection(page: import('@playwright/test').Page) {
   await page.getByRole('link', { name: 'Settings' }).click()
@@ -59,8 +72,10 @@ test('Turn all off empties the tray of every non-built-in tool; turn all on rest
   await toggleAll.click()
   await expect(toggleAll).toHaveText('Turn all on')
 
-  // Every row but card now shows its toggle off.
-  for (const id of ['note', 'area', 'table', 'image', 'pencil', 'eraser', 'laser', 'shape']) {
+  // Every row but card now shows its toggle off -- including the
+  // tool-less nouns (diagram, sheet), which have no tray button to
+  // empty but still participate in the bulk toggle.
+  for (const id of ['note', 'area', 'table', 'image', 'pencil', 'eraser', 'laser', 'shape', 'diagram', 'sheet']) {
     const toggle = page.locator(`[data-testid="extensions-row"][data-extension-id="${id}"]`).getByTestId('extensions-row-toggle').getByRole('button')
     await expect(toggle).toHaveAttribute('data-checked', 'false')
   }
@@ -80,7 +95,7 @@ test('Turn all off empties the tray of every non-built-in tool; turn all on rest
   await expect(toggleAll).toHaveText('Turn all on')
   await toggleAll.click()
   await expect(toggleAll).toHaveText('Turn all off')
-  for (const id of ['note', 'area', 'table', 'image', 'pencil', 'eraser', 'laser', 'shape']) {
+  for (const id of ['note', 'area', 'table', 'image', 'pencil', 'eraser', 'laser', 'shape', 'diagram', 'sheet']) {
     const toggle = page.locator(`[data-testid="extensions-row"][data-extension-id="${id}"]`).getByTestId('extensions-row-toggle').getByRole('button')
     await expect(toggle).toHaveAttribute('data-checked', 'true')
   }
@@ -90,9 +105,10 @@ test('Extensions section lists every registered canvas tool; the built-in card r
   await page.goto('/')
   await openExtensionsSection(page)
 
-  // Every ATLAS_TOOLS member (atlas/atlasTools.ts) gets exactly one
-  // row -- card, note, area, table, image, pencil, eraser, laser, shape.
-  await expect(page.getByTestId('extensions-row')).toHaveCount(9)
+  // Every ATLAS_TOOLS member (atlas/atlasTools.ts) plus every
+  // tool-less noun (diagram, sheet) gets exactly one row -- card, note,
+  // area, table, image, pencil, eraser, laser, shape, diagram, sheet.
+  await expect(page.getByTestId('extensions-row')).toHaveCount(11)
 
   const cardRow = page.locator('[data-testid="extensions-row"][data-extension-id="card"]')
   await expect(cardRow).toBeVisible()
@@ -105,6 +121,40 @@ test('Extensions section lists every registered canvas tool; the built-in card r
   await expect(tableToggle).toHaveAttribute('data-checked', 'true')
 })
 
+test('A tool-less noun (diagram, sheet) gets a row with a toggle and states its narrower disable scope', async ({ page }) => {
+  await page.goto('/')
+  await openExtensionsSection(page)
+
+  const diagramRow = page.locator('[data-testid="extensions-row"][data-extension-id="diagram"]')
+  await expect(diagramRow).toBeVisible()
+  await expect(diagramRow.getByTestId('extensions-row-toggle').getByRole('button')).toHaveAttribute('data-checked', 'true')
+  await diagramRow.locator('summary').click()
+  await expect(diagramRow.getByTestId('extensions-row-description')).toHaveText(
+    'View and edit diagrams — draw.io files open in the real editor.',
+  )
+  await expect(diagramRow.getByTestId('extensions-row-disable-scope')).toHaveText(
+    'Turning this off stops new diagrams from landing on drop and closes the built-in editor. Diagrams already on the board keep working.',
+  )
+
+  const sheetRow = page.locator('[data-testid="extensions-row"][data-extension-id="sheet"]')
+  await expect(sheetRow).toBeVisible()
+  await expect(sheetRow.getByTestId('extensions-row-toggle').getByRole('button')).toHaveAttribute('data-checked', 'true')
+  await sheetRow.locator('summary').click()
+  await expect(sheetRow.getByTestId('extensions-row-description')).toHaveText(
+    'Preview spreadsheets and CSV files dropped onto the board.',
+  )
+  await expect(sheetRow.getByTestId('extensions-row-disable-scope')).toHaveText(
+    'Turning this off stops new sheets from landing on drop. Sheets already on the board keep working, including opening in your default app.',
+  )
+
+  // A tray tool's row never shows a disable-scope note -- its toggle's
+  // scope (tray button + palette command) is already the standing
+  // default every row implicitly shares.
+  const tableRow = page.locator('[data-testid="extensions-row"][data-extension-id="table"]')
+  await tableRow.locator('summary').click()
+  await expect(tableRow.getByTestId('extensions-row-disable-scope')).toHaveCount(0)
+})
+
 test('Disabling a tool removes it from the tray and palette, keeps existing objects rendering, and persists across reload', async ({ page }) => {
   await page.goto('/')
   await page.getByRole('link', { name: 'Atlas' }).click()
diff --git a/frontend/src/atlas/atlasNounDeclarationFields.json b/frontend/src/atlas/atlasNounDeclarationFields.json
index 11c87f35..7244b593 100644
--- a/frontend/src/atlas/atlasNounDeclarationFields.json
+++ b/frontend/src/atlas/atlasNounDeclarationFields.json
@@ -77,7 +77,7 @@
   {
     "field": "content",
     "legalValues": "an object with Component (a React component accepting { object, mirrorVersion }), ariaLabelKey (a string), and role ('img' or undefined) -- or null",
-    "meaning": "this noun's own placed-instance content contribution. registerNoun() feeds it into the board-object content registry (atlasNounRegistry.ts's registerBoardObjectContent) whenever boardObjectKind is non-null, killing AtlasBoardObjectNode.tsx's former per-Kind hand branch. A tool-less noun (diagram) calls registerBoardObjectContent directly instead of declaring this field at all, since it has no AtlasToolShape to satisfy. mirrorVersion bumps on a live disk change to a fileBacked Kind's own mirrored file (see fileBacked below) -- a non-file-backed Component simply ignores it."
+    "meaning": "this noun's own placed-instance content contribution. registerNoun() feeds it into the board-object content registry (atlasNounRegistry.ts's registerBoardObjectContent) whenever boardObjectKind is non-null, killing AtlasBoardObjectNode.tsx's former per-Kind hand branch. A tool-less noun (diagram, sheet) calls registerBoardObjectContent directly instead of declaring this field at all, since it has no AtlasToolShape to satisfy -- it instead sets this same content shape's own optional `extension` member (icon, label, description, disableScopeNote) so Settings > Extensions can still render an honest row for it. mirrorVersion bumps on a live disk change to a fileBacked Kind's own mirrored file (see fileBacked below) -- a non-file-backed Component simply ignores it."
   },
   {
     "field": "capabilities",
diff --git a/frontend/src/atlas/atlasNounRegistry.ts b/frontend/src/atlas/atlasNounRegistry.ts
index de1b8b00..f3fd23e9 100644
--- a/frontend/src/atlas/atlasNounRegistry.ts
+++ b/frontend/src/atlas/atlasNounRegistry.ts
@@ -93,6 +93,32 @@ export interface AtlasNounContent {
   // RESOLVER -- see EditRouteDecl's own header for why a single Kind
   // (diagram) needs the function form.
   editRoute?: EditRouteDecl
+  // extension (goal 0237 S3 rider): Settings > Extensions row metadata
+  // for a NOUN WITH NO TRAY TOOL. A tool-bearing noun already carries
+  // icon/label/description on its own AtlasToolShapeBase descriptor
+  // (registerNoun below), so this stays undefined there; a tool-less
+  // noun (diagram, sheet -- file-drop only, no AtlasToolShape to
+  // declare these on) sets it directly in its own registerBoardObjectContent
+  // call so the Extensions list can render an honest row for it too,
+  // mirroring goal 0211's own description-field precedent. Presence of
+  // this field is exactly how toolLessNounExtensions() below finds a
+  // tool-less noun worth listing.
+  extension?: ExtensionRowMeta
+}
+
+// ExtensionRowMeta -- the fields ExtensionRow.tsx needs for a tool-less
+// noun's own row that AtlasToolShapeBase would otherwise supply.
+// disableScopeNote is REQUIRED (never optional): a tool-less noun has
+// no tray button to hide, so its own disable toggle gates a narrower,
+// noun-specific seam (file-drop routing, and for diagram the embedded-
+// editor door) -- the row must always say so rather than silently
+// implying the same tray-wide scope a tool row's toggle has.
+export interface ExtensionRowMeta {
+  icon: Icon
+  label: string
+  description: string
+  disableScopeNote: string
+  capabilities?: readonly string[]
 }
 
 // AtlasBoardObjectContent -- AtlasNounContent plus the board-facts
@@ -110,7 +136,7 @@ export interface AtlasNounContent {
 // than independently settable -- a Kind with no source still declares
 // this field directly (shape/ink today), so the field itself stays
 // required.
-interface AtlasBoardObjectContent extends AtlasNounContent {
+export interface AtlasBoardObjectContent extends AtlasNounContent {
   dragBand: boolean
   fileBacked: boolean
 }
@@ -146,6 +172,34 @@ export function boardObjectContentFor(kind: string): AtlasBoardObjectContent | u
   return boardObjectContentRegistry.get(kind as AtlasBoardObjectKind)
 }
 
+// ToolLessNounExtension -- one entry of toolLessNounExtensions() below,
+// with `extension` already narrowed to non-optional (the filter that
+// builds this array is the one place that check happens, so every
+// consumer downstream gets a guaranteed ExtensionRowMeta instead of
+// re-checking for undefined itself).
+export interface ToolLessNounExtension {
+  kind: AtlasBoardObjectKind
+  content: AtlasBoardObjectContent
+  extension: ExtensionRowMeta
+}
+
+// toolLessNounExtensions -- every registered noun with NO AtlasToolShape
+// of its own (diagram, sheet: file-drop only) that has declared
+// Extensions-row metadata, so Settings > Extensions (ExtensionsSection.tsx)
+// can list it alongside every tray tool. A tool-bearing noun's content
+// also lives in this same registry (registerNoun folds it in below) but
+// never sets `extension`, so it's excluded here -- it already gets its
+// own row from ATLAS_TOOLS directly. Sorted by kind for a stable,
+// deterministic row order independent of import.meta.glob's own
+// alphabetical file-discovery order.
+export function toolLessNounExtensions(): ToolLessNounExtension[] {
+  const found: ToolLessNounExtension[] = []
+  for (const [kind, content] of boardObjectContentRegistry.entries()) {
+    if (content.extension) found.push({ kind, content, extension: content.extension })
+  }
+  return found.sort((a, b) => a.kind.localeCompare(b.kind))
+}
+
 interface AtlasToolShapeBase {
   icon: Icon
   label: string
diff --git a/frontend/src/atlas/tools/diagramNoun.ts b/frontend/src/atlas/tools/diagramNoun.ts
index 2385f2f2..f9bada5e 100644
--- a/frontend/src/atlas/tools/diagramNoun.ts
+++ b/frontend/src/atlas/tools/diagramNoun.ts
@@ -1,4 +1,5 @@
 import { lazy } from 'react'
+import { FlowchartIcon } from '@primer/octicons-react'
 import type { BoardObject } from '../../../bindings/github.com/alicoding/mill/internal/domain/atlas/models'
 import { registerBoardObjectContent } from '../atlasNounRegistry'
 import { isDrawioEditableExtension } from '../atlasDiagramMirror'
@@ -45,4 +46,16 @@ registerBoardObjectContent('diagram', {
       ? { kind: 'embedded-engine', engine: 'drawio' }
       : { kind: 'external-app' }
   ),
+  // extension (goal 0237 S3 rider): the Settings > Extensions row for
+  // this tool-less noun. disableScopeNote states its scope honestly --
+  // there is no tray button to hide, so the toggle instead gates
+  // useAtlasNativeFileDrop.ts's own routing (a disabled drop falls
+  // through to the plain card path) and dispatchObjectEdit's
+  // embedded-engine arm (objectSeams.ts, already keyed off object.Kind).
+  extension: {
+    icon: FlowchartIcon,
+    label: 'Diagram',
+    description: 'View and edit diagrams — draw.io files open in the real editor.',
+    disableScopeNote: 'Turning this off stops new diagrams from landing on drop and closes the built-in editor. Diagrams already on the board keep working.',
+  },
 })
diff --git a/frontend/src/atlas/tools/sheetNoun.ts b/frontend/src/atlas/tools/sheetNoun.ts
index be11b8bb..a9fb9680 100644
--- a/frontend/src/atlas/tools/sheetNoun.ts
+++ b/frontend/src/atlas/tools/sheetNoun.ts
@@ -1,4 +1,5 @@
 import { lazy } from 'react'
+import { ColumnsIcon } from '@primer/octicons-react'
 import { registerBoardObjectContent } from '../atlasNounRegistry'
 
 // Lazy-imported (React.lazy + Suspense, AtlasBoardObjectNode.tsx's own
@@ -40,4 +41,16 @@ registerBoardObjectContent('sheet', {
   // directly.
   source: { kind: 'file', pathKey: 'mirrorPath' },
   editRoute: { kind: 'external-app' },
+  // extension (goal 0237 S3 rider): the Settings > Extensions row for
+  // this tool-less noun. disableScopeNote states its scope honestly --
+  // there is no tray button to hide and no embedded editor to close
+  // (editRoute above is a static 'external-app', which dispatchObjectEdit
+  // never gates), so the toggle only affects
+  // useAtlasNativeFileDrop.ts's own routing.
+  extension: {
+    icon: ColumnsIcon,
+    label: 'Sheet',
+    description: 'Preview spreadsheets and CSV files dropped onto the board.',
+    disableScopeNote: 'Turning this off stops new sheets from landing on drop. Sheets already on the board keep working, including opening in your default app.',
+  },
 })
diff --git a/frontend/src/atlas/useAtlasNativeFileDrop.test.ts b/frontend/src/atlas/useAtlasNativeFileDrop.test.ts
new file mode 100644
index 00000000..e2dc2836
--- /dev/null
+++ b/frontend/src/atlas/useAtlasNativeFileDrop.test.ts
@@ -0,0 +1,39 @@
+import { describe, expect, it } from 'vitest'
+import { resolveFileDropKind } from './useAtlasNativeFileDrop'
+
+const alwaysEnabled = () => true
+const alwaysDisabled = () => false
+
+describe('resolveFileDropKind (goal 0237 S3 rider)', () => {
+  it('routes a diagram path to "diagram" when the diagram extension is enabled', () => {
+    expect(resolveFileDropKind('/tmp/plan.drawio', alwaysEnabled)).toBe('diagram')
+  })
+
+  // Regression: disabling diagram from Settings > Extensions has no
+  // tray button to remove (diagram is file-drop only), so it must
+  // instead fall the drop through to the generic card path.
+  it('falls a disabled diagram drop through to the "card" path', () => {
+    expect(resolveFileDropKind('/tmp/plan.drawio', alwaysDisabled)).toBe('card')
+    expect(resolveFileDropKind('/tmp/flow.mmd', (id) => id !== 'diagram')).toBe('card')
+  })
+
+  it('routes a sheet path to "sheet" when the sheet extension is enabled', () => {
+    expect(resolveFileDropKind('/tmp/data.xlsx', alwaysEnabled)).toBe('sheet')
+    expect(resolveFileDropKind('/tmp/data.csv', alwaysEnabled)).toBe('sheet')
+  })
+
+  // Regression: same fall-through as diagram -- sheet has no tray
+  // button either.
+  it('falls a disabled sheet drop through to the "card" path', () => {
+    expect(resolveFileDropKind('/tmp/data.xlsx', alwaysDisabled)).toBe('card')
+    expect(resolveFileDropKind('/tmp/data.csv', (id) => id !== 'sheet')).toBe('card')
+  })
+
+  it('routes an image path to "image" regardless of diagram/sheet enablement', () => {
+    expect(resolveFileDropKind('/tmp/photo.png', alwaysDisabled)).toBe('image')
+  })
+
+  it('falls an unrelated extension through to "card"', () => {
+    expect(resolveFileDropKind('/tmp/notes.md', alwaysEnabled)).toBe('card')
+  })
+})
diff --git a/frontend/src/atlas/useAtlasNativeFileDrop.ts b/frontend/src/atlas/useAtlasNativeFileDrop.ts
index 1761d1e1..1a142d4c 100644
--- a/frontend/src/atlas/useAtlasNativeFileDrop.ts
+++ b/frontend/src/atlas/useAtlasNativeFileDrop.ts
@@ -4,6 +4,7 @@ import { Events } from '@wailsio/runtime'
 import { AtlasService } from '../shared/bindings'
 import { titleFromFilename } from './atlasCreateHelpers'
 import { refreshAtlas } from './atlasStore'
+import { isExtensionEnabled } from '../shared/extensionEnablementStore'
 import { useAtlasFolderImportRequestStore } from './atlasFolderImportRequest'
 import { FILE_DROP_EVENT_NAME, FILE_DROP_CONTEXT_BOARD } from './atlasFileDropShared'
 import { frameContainingPoint } from './atlasFramePoint'
@@ -16,6 +17,26 @@ const DROP_ERROR_MS = 4000
 const PULSE_MS = 1200
 const PULSE_MS_REDUCED = 1500
 
+// resolveFileDropKind -- the pure routing decision behind the Events.On
+// handler below: which board-object kind a resolved drop path lands
+// as, or 'card' for the generic reference-card fallback. Pulled out as
+// its own function (goal 0237 S3 rider) purely so it's Vitest-testable
+// on its own -- the real OS drop GESTURE that reaches it is a
+// structural e2e gap (testing.md's own manual-only registry:
+// WindowFilesDropped needs a real *WebviewWindow, which server-mode
+// Playwright's connection is not), but this decision is plain data in,
+// data out. isEnabled is injected rather than read from the store
+// directly so a test can drive both branches without touching global
+// state.
+export type FileDropKind = 'diagram' | 'image' | 'sheet' | 'card'
+
+export function resolveFileDropKind(path: string, isEnabled: (id: string) => boolean): FileDropKind {
+  if (isDiagramPath(path) && isEnabled('diagram')) return 'diagram'
+  if (isImagePath(path)) return 'image'
+  if (isSheetPath(path) && isEnabled('sheet')) return 'sheet'
+  return 'card'
+}
+
 // The board-context half of the native OS file-drop door (goal 0081
 // slice A3, LOCKED design §3b): a single non-directory file lands
 // instantly at the drop point (a brief settle pulse, the ⌘K jump
@@ -63,34 +84,31 @@ export function useAtlasNativeFileDrop({ parentID, topLevelBoxes, screenToFlowPo
             return
           }
           const path = route.Path
-          // A dropped .drawio/.mmd/.mermaid file lands as a "diagram"
-          // board object, never a card (goal 0179 S2) -- no pulse/
-          // duplicate-notice machinery applies, since a board object
-          // carries neither.
-          if (isDiagramPath(path)) {
-            return diagramCreate.land(path, targetParentID, { X: point.x, Y: point.y })
-          }
-          // A dropped image file lands as an "image" board object the
-          // same way (goal 0206, 0179's founding rule): the reference-
-          // card fallback below is scoped to non-image, non-diagram
-          // drops now.
-          if (isImagePath(path)) {
-            return imageCreate.land(path, targetParentID, { X: point.x, Y: point.y })
-          }
-          // A dropped .xlsx/.csv file lands as a "sheet" board object
-          // the same way (goal 0232 S2) -- the reference-card fallback
-          // below is scoped to non-image, non-diagram, non-sheet drops.
-          if (isSheetPath(path)) {
-            return sheetCreate.land(path, targetParentID, { X: point.x, Y: point.y })
+          // A dropped .drawio/.mmd/.mermaid or .xlsx/.csv file lands as
+          // its own board object, never a card (goal 0179 S2, goal
+          // 0232 S2) -- no pulse/duplicate-notice machinery applies to
+          // either, since a board object carries neither. Disabling
+          // diagram/sheet from Settings > Extensions (goal 0237 S3
+          // rider -- neither noun has a tray button to hide) falls the
+          // drop through to the plain-card path instead, exactly the
+          // resolveFileDropKind decision above states.
+          switch (resolveFileDropKind(path, isExtensionEnabled)) {
+            case 'diagram':
+              return diagramCreate.land(path, targetParentID, { X: point.x, Y: point.y })
+            case 'image':
+              return imageCreate.land(path, targetParentID, { X: point.x, Y: point.y })
+            case 'sheet':
+              return sheetCreate.land(path, targetParentID, { X: point.x, Y: point.y })
+            case 'card':
+              return AtlasService.CreateCardFromFileDrop(path, titleFromFilename(path), targetParentID, { X: point.x, Y: point.y })
+                .then((result) => refreshAtlas().then(() => {
+                  pulse(result.Card.ID)
+                  window.setTimeout(() => pulse(null), reduced ? PULSE_MS_REDUCED : PULSE_MS)
+                  if (result.DuplicateOfTitle) {
+                    setDropDuplicateNotice(t('board.dropDuplicateNotice', { title: result.DuplicateOfTitle }))
+                  }
+                }))
           }
-          return AtlasService.CreateCardFromFileDrop(path, titleFromFilename(path), targetParentID, { X: point.x, Y: point.y })
-            .then((result) => refreshAtlas().then(() => {
-              pulse(result.Card.ID)
-              window.setTimeout(() => pulse(null), reduced ? PULSE_MS_REDUCED : PULSE_MS)
-              if (result.DuplicateOfTitle) {
-                setDropDuplicateNotice(t('board.dropDuplicateNotice', { title: result.DuplicateOfTitle }))
-              }
-            }))
         })
         .catch(() => setDropError(t('capture.dropError')))
     })
diff --git a/frontend/src/views/ExtensionRow.tsx b/frontend/src/views/ExtensionRow.tsx
index 6d8435c7..96cdbcce 100644
--- a/frontend/src/views/ExtensionRow.tsx
+++ b/frontend/src/views/ExtensionRow.tsx
@@ -1,9 +1,8 @@
 import { ChevronRightIcon } from '@primer/octicons-react'
 import { useTranslation } from 'react-i18next'
 import { Label, Link, Stack, Text, ToggleSwitch } from '@primer/react'
-import type { AtlasToolShape } from '../atlas/atlasTools'
 import { useAppStore } from '../shared/store'
-import { descriptionLabel, editRouteLabel, groupLabel, reachLabel, sourceLabel, versionLabel } from './extensionMeta'
+import { descriptionLabel, editRouteLabel, groupLabel, reachLabel, sourceLabel, versionLabel, type ExtensionRowSource } from './extensionMeta'
 import listStyles from '../shared/ListCard.module.css'
 import styles from './ExtensionsSection.module.css'
 
@@ -15,46 +14,53 @@ const ATLAS_CONCEPTS_DOCS_PAGE = 'concepts/atlas.md'
 // ExtensionRow -- one row of Settings > Extensions, collapsed to
 // icon/label/meta by default, expanding (native <details>, see
 // ExtensionsSection.module.css's own header comment) into a registry-
-// derived detail panel: description, meta chips, the honest reach
-// line, the app's own build version, and the shared Docs link. Every
-// value here is READ off the tool's own registered descriptor
-// (atlas/atlasNounRegistry.ts) -- nothing here is hand-curated per
-// extension.
-export function ExtensionRow({ tool, builtIn, enabled, appVersion, onToggle }: {
-  tool: AtlasToolShape
+// derived detail panel: description, meta chips, an optional disable-
+// scope note, the honest reach line, the app's own build version, and
+// the shared Docs link. Every value here is READ off the noun's own
+// registered descriptor, normalized into ExtensionRowSource by
+// extensionMeta.ts's toolRowSource/toolLessRowSource -- nothing here is
+// hand-curated per extension, and this component never itself branches
+// on whether the row came from a tray tool or a tool-less noun.
+export function ExtensionRow({ row, builtIn, enabled, appVersion, onToggle }: {
+  row: ExtensionRowSource
   builtIn: boolean
   enabled: boolean
   appVersion: string
   onToggle: (enabled: boolean) => void
 }) {
   const { t } = useTranslation('views')
-  const Icon = tool.icon
-  const labelId = `extension-row-label-${tool.id}`
-  const meta = [groupLabel(tool.group), sourceLabel(tool.content?.source), editRouteLabel(tool.content?.editRoute)]
+  const Icon = row.icon
+  const labelId = `extension-row-label-${row.id}`
+  const meta = [row.group ? groupLabel(row.group) : null, sourceLabel(row.source), editRouteLabel(row.editRoute)]
     .filter((m): m is string => m !== null)
 
   return (
-    <div className={styles.row} data-testid="extensions-row" data-extension-id={tool.id}>
+    <div className={styles.row} data-testid="extensions-row" data-extension-id={row.id}>
       <details className={styles.details}>
         <summary className={styles.summary}>
           <ChevronRightIcon className={styles.chevron} size={16} />
           <Icon size={16} />
           <Stack direction="vertical" gap="none">
-            <Text id={labelId} size="small" weight="semibold">{tool.label}</Text>
+            <Text id={labelId} size="small" weight="semibold">{row.label}</Text>
             {meta.length > 0 && (
               <Text size="small" className={listStyles.muted}>{meta.join(' · ')}</Text>
             )}
           </Stack>
         </summary>
         <div className={styles.expanded} data-testid="extensions-row-expanded">
-          <Text as="p" size="small" data-testid="extensions-row-description">{descriptionLabel(tool)}</Text>
+          <Text as="p" size="small" data-testid="extensions-row-description">{descriptionLabel(row)}</Text>
           {meta.length > 0 && (
             <Stack direction="horizontal" gap="condensed" className={styles.chips}>
               {meta.map((chip) => <Label key={chip}>{chip}</Label>)}
             </Stack>
           )}
+          {row.disableScopeNote && (
+            <Text as="p" size="small" className={listStyles.muted} data-testid="extensions-row-disable-scope">
+              {row.disableScopeNote}
+            </Text>
+          )}
           <Text as="p" size="small" className={listStyles.muted} data-testid="extensions-row-reach">
-            {reachLabel(tool.capabilities)}
+            {reachLabel(row.capabilities)}
           </Text>
           {appVersion && (
             <Text as="p" size="small" className={listStyles.muted} data-testid="extensions-row-version">
diff --git a/frontend/src/views/ExtensionsSection.tsx b/frontend/src/views/ExtensionsSection.tsx
index d3066279..00f86838 100644
--- a/frontend/src/views/ExtensionsSection.tsx
+++ b/frontend/src/views/ExtensionsSection.tsx
@@ -2,33 +2,45 @@ import { useEffect, useState } from 'react'
 import { useTranslation } from 'react-i18next'
 import { ActionList, Button, Stack, Text } from '@primer/react'
 import { ATLAS_TOOLS, type AtlasToolID } from '../atlas/atlasTools'
+import { toolLessNounExtensions } from '../atlas/atlasNounRegistry'
 import { SettingsService } from '../shared/bindings'
 import { refreshDisabledExtensions, useExtensionEnablementStore } from '../shared/extensionEnablementStore'
 import { ExtensionRow } from './ExtensionRow'
+import { toolLessRowSource, toolRowSource, type ExtensionRowSource } from './extensionMeta'
 import styles from '../shared/ListCard.module.css'
 
 // Settings > Extensions (goal 0237 S2, extended by goal 0211's plugin-
-// manager UX slice): a registry-DERIVED list of every registered
-// canvas tool, each expandable into a registry-derived detail panel
-// (ExtensionRow.tsx) -- never a hand-curated array, so a new tool's own
-// registerNoun() call (atlasNounRegistry.ts) makes it appear here with
-// zero edits to this file. `card` is the one exception: it's the
+// manager UX slice, and by goal 0237 S3's rider): a registry-DERIVED
+// list of every registered NOUN -- every tray tool (ATLAS_TOOLS) plus
+// every tool-less noun that declares Extensions-row metadata
+// (toolLessNounExtensions(), diagram/sheet today) -- each expandable
+// into a registry-derived detail panel (ExtensionRow.tsx) via one
+// normalized row shape (extensionMeta.ts's ExtensionRowSource). Never a
+// hand-curated array: a new tray tool's registerNoun() call or a new
+// tool-less noun's own `extension` declaration both make it appear here
+// with zero edits to this file. `card` is the one exception: it's the
 // kernel knowledge object (ADR-0046), not a guest extension, so its row
 // renders a "Built-in" label instead of a toggle -- shown rather than
 // omitted, so the Extensions list still reads as a complete inventory
-// of every canvas tool, not a mysteriously-short one.
+// of every canvas noun, not a mysteriously-short one.
 //
-// Disabling a tool here only changes what CAN be created from now on:
-// it removes the tool's own button from the creation tray
+// Disabling a TRAY tool here only changes what CAN be created from now
+// on: it removes the tool's own button from the creation tray
 // (AtlasCreationTray.tsx's own ATLAS_TOOLS.filter) and its
 // `atlas.create.<id>` command from the palette/keyboard
 // (shared/commands.ts's own `enabled()` predicate) -- existing board
 // objects of that kind keep rendering exactly as before, since neither
 // the board's own render path nor AtlasBoardObjectNode.tsx's content
 // lookup (atlasNounRegistry.ts's boardObjectContentFor) ever consults
-// this list at all.
+// this list at all. A TOOL-LESS noun has no tray button to remove --
+// its own row states its narrower disable scope directly (see each
+// noun's own `extension.disableScopeNote`, atlasNounRegistry.ts).
 const CARD_TOOL_ID: AtlasToolID = 'card'
-const NON_BUILT_IN_IDS: AtlasToolID[] = ATLAS_TOOLS.filter((t) => t.id !== CARD_TOOL_ID).map((t) => t.id)
+const EXTENSION_ROWS: ExtensionRowSource[] = [
+  ...ATLAS_TOOLS.map(toolRowSource),
+  ...toolLessNounExtensions().map(toolLessRowSource),
+]
+const NON_BUILT_IN_IDS: string[] = EXTENSION_ROWS.filter((r) => r.id !== CARD_TOOL_ID).map((r) => r.id)
 
 export default function ExtensionsSection() {
   const { t } = useTranslation('views')
@@ -40,7 +52,7 @@ export default function ExtensionsSection() {
     SettingsService.AppVersion().then(setAppVersion).catch(console.error)
   }, [])
 
-  const toggle = (id: AtlasToolID, enabled: boolean) => {
+  const toggle = (id: string, enabled: boolean) => {
     SettingsService.SetExtensionEnabled(id, enabled).then(refreshDisabledExtensions).catch(console.error)
   }
 
@@ -77,14 +89,14 @@ export default function ExtensionsSection() {
         </Button>
       </Stack>
       <ActionList role="list" showDividers data-testid="extensions-list">
-        {ATLAS_TOOLS.map((tool) => (
-          <ActionList.Item key={tool.id}>
+        {EXTENSION_ROWS.map((row) => (
+          <ActionList.Item key={row.id}>
             <ExtensionRow
-              tool={tool}
-              builtIn={tool.id === CARD_TOOL_ID}
-              enabled={!disabledIds.includes(tool.id)}
+              row={row}
+              builtIn={row.id === CARD_TOOL_ID}
+              enabled={!disabledIds.includes(row.id)}
               appVersion={appVersion}
-              onToggle={(enabled) => toggle(tool.id, enabled)}
+              onToggle={(enabled) => toggle(row.id, enabled)}
             />
           </ActionList.Item>
         ))}
diff --git a/frontend/src/views/extensionMeta.test.ts b/frontend/src/views/extensionMeta.test.ts
index a95dc917..f57c18e2 100644
--- a/frontend/src/views/extensionMeta.test.ts
+++ b/frontend/src/views/extensionMeta.test.ts
@@ -1,5 +1,10 @@
 import { describe, expect, it } from 'vitest'
-import { descriptionLabel, editRouteLabel, groupLabel, reachLabel, sourceLabel, versionLabel } from './extensionMeta'
+import { ATLAS_TOOLS } from '../atlas/atlasTools'
+import { toolLessNounExtensions } from '../atlas/atlasNounRegistry'
+import {
+  descriptionLabel, editRouteLabel, groupLabel, reachLabel, sourceLabel, versionLabel,
+  toolLessRowSource, toolRowSource,
+} from './extensionMeta'
 
 describe('groupLabel', () => {
   it('maps every declared group to user-facing text', () => {
@@ -68,3 +73,38 @@ describe('versionLabel', () => {
     expect(versionLabel('1.2.3')).toBe('Ships with Mill v1.2.3')
   })
 })
+
+describe('toolRowSource (goal 0237 S3 rider)', () => {
+  it('normalizes a tray tool into a row, carrying its group and content declarations', () => {
+    const shape = ATLAS_TOOLS.find((t) => t.id === 'shape')!
+    const row = toolRowSource(shape)
+    expect(row).toEqual({
+      id: 'shape',
+      icon: shape.icon,
+      label: shape.label,
+      description: shape.description,
+      group: shape.group,
+      source: shape.content?.source,
+      editRoute: shape.content?.editRoute,
+      capabilities: shape.capabilities,
+    })
+  })
+})
+
+describe('toolLessRowSource (goal 0237 S3 rider)', () => {
+  it('normalizes a tool-less noun into a row, with no group chip and its own disableScopeNote', () => {
+    const diagram = toolLessNounExtensions().find((e) => e.kind === 'diagram')!
+    const row = toolLessRowSource(diagram)
+    expect(row).toEqual({
+      id: 'diagram',
+      icon: diagram.extension.icon,
+      label: diagram.extension.label,
+      description: diagram.extension.description,
+      source: diagram.content.source,
+      editRoute: diagram.content.editRoute,
+      capabilities: diagram.extension.capabilities,
+      disableScopeNote: diagram.extension.disableScopeNote,
+    })
+    expect(row.group).toBeUndefined()
+  })
+})
diff --git a/frontend/src/views/extensionMeta.ts b/frontend/src/views/extensionMeta.ts
index ba0d3064..d30b6560 100644
--- a/frontend/src/views/extensionMeta.ts
+++ b/frontend/src/views/extensionMeta.ts
@@ -1,5 +1,7 @@
+import type { Icon } from '@primer/octicons-react'
 import type { EditRouteDecl, ObjectSource } from '../atlas/objectSeams'
 import type { AtlasToolShape } from '../atlas/atlasTools'
+import type { ToolLessNounExtension } from '../atlas/atlasNounRegistry'
 
 // Pure enum -> user-vocabulary mapping for the Extensions section
 // (Settings > Extensions). Kept in its own file, apart from
@@ -10,6 +12,62 @@ import type { AtlasToolShape } from '../atlas/atlasTools'
 // keeps its own pure formatter/description logic inline since none of
 // them branch on an enum this way.
 
+// ExtensionRowSource -- the ONE row shape ExtensionRow.tsx renders,
+// normalized from either a tray tool (AtlasToolShape) or a tool-less
+// noun (ToolLessNounExtension) by the two builders below -- so the row
+// component itself never branches on which kind of noun it's showing.
+// group/description/capabilities/disableScopeNote stay optional: a
+// tool-less noun has no tray cluster to report (there is no `group`
+// chip for a noun with no tray at all) and only IT ever sets
+// disableScopeNote, since only it needs to say its toggle's scope
+// differs from a tray tool's.
+export interface ExtensionRowSource {
+  id: string
+  icon: Icon
+  label: string
+  description?: string
+  group?: AtlasToolShape['group']
+  source?: ObjectSource
+  editRoute?: EditRouteDecl
+  capabilities?: readonly string[]
+  disableScopeNote?: string
+}
+
+// toolRowSource -- every ATLAS_TOOLS member becomes a row exactly as it
+// already did before goal 0237 S3's rider (ExtensionsSection.tsx used
+// to read AtlasToolShape fields directly); this is that same read,
+// pulled out so it composes with toolLessRowSource below into one list.
+export function toolRowSource(tool: AtlasToolShape): ExtensionRowSource {
+  return {
+    id: tool.id,
+    icon: tool.icon,
+    label: tool.label,
+    description: tool.description,
+    group: tool.group,
+    source: tool.content?.source,
+    editRoute: tool.content?.editRoute,
+    capabilities: tool.capabilities,
+  }
+}
+
+// toolLessRowSource -- a tool-less noun's own row (goal 0237 S3 rider):
+// icon/label/description/disableScopeNote come from its declared
+// `extension` (atlasNounRegistry.ts's ExtensionRowMeta), source/
+// editRoute from the same content declaration a tray tool's row reads,
+// and no `group` -- there is no tray cluster to report honestly.
+export function toolLessRowSource({ kind, content, extension }: ToolLessNounExtension): ExtensionRowSource {
+  return {
+    id: kind,
+    icon: extension.icon,
+    label: extension.label,
+    description: extension.description,
+    source: content.source,
+    editRoute: content.editRoute,
+    capabilities: extension.capabilities,
+    disableScopeNote: extension.disableScopeNote,
+  }
+}
+
 // groupLabel -- AtlasToolShape.group's own three clusters, restated as
 // short chip text a user would recognize (never the tray's own
 // internal cluster name).
diff --git a/userdocs/llms-full.txt b/userdocs/llms-full.txt
index d530744d..a2eacf74 100644
--- a/userdocs/llms-full.txt
+++ b/userdocs/llms-full.txt
@@ -1420,7 +1420,7 @@ are never omissions.
 | `boardNodeType` | 'atlas-note', 'atlas-sticky', 'atlas-group', 'atlas-object', or null | which shared React Flow node component renders this noun's placed instance. null for a tool whose gesture never persists a renderable instance (eraser, laser). |
 | `dragBand` | boolean -- REQUIRED, never optional | only load-bearing when boardNodeType is 'atlas-object': does this noun's own content capture pointer events (a grid, a vendored pan/zoom viewer), so the shared renderer needs to add its own chrome band as the drag surface? A noun whose whole body already drags declares false, not omitted. |
 | `boardObjectKind` | 'shape', 'image', 'ink', 'table', 'diagram', 'sheet', or null | the persisted BoardObject.Kind this noun's own placed instance carries, or null for a tool that never routes through the shared 'atlas-object' renderer. Not always equal to id -- pencil's own placed instance is Kind 'ink' -- so content resolution below keys off this field, read from object.Kind, never off id. |
-| `content` | an object with Component (a React component accepting { object, mirrorVersion }), ariaLabelKey (a string), and role ('img' or undefined) -- or null | this noun's own placed-instance content contribution. registerNoun() feeds it into the board-object content registry (atlasNounRegistry.ts's registerBoardObjectContent) whenever boardObjectKind is non-null, killing AtlasBoardObjectNode.tsx's former per-Kind hand branch. A tool-less noun (diagram) calls registerBoardObjectContent directly instead of declaring this field at all, since it has no AtlasToolShape to satisfy. mirrorVersion bumps on a live disk change to a fileBacked Kind's own mirrored file (see fileBacked below) -- a non-file-backed Component simply ignores it. |
+| `content` | an object with Component (a React component accepting { object, mirrorVersion }), ariaLabelKey (a string), and role ('img' or undefined) -- or null | this noun's own placed-instance content contribution. registerNoun() feeds it into the board-object content registry (atlasNounRegistry.ts's registerBoardObjectContent) whenever boardObjectKind is non-null, killing AtlasBoardObjectNode.tsx's former per-Kind hand branch. A tool-less noun (diagram, sheet) calls registerBoardObjectContent directly instead of declaring this field at all, since it has no AtlasToolShape to satisfy -- it instead sets this same content shape's own optional `extension` member (icon, label, description, disableScopeNote) so Settings > Extensions can still render an honest row for it. mirrorVersion bumps on a live disk change to a fileBacked Kind's own mirrored file (see fileBacked below) -- a non-file-backed Component simply ignores it. |
 | `capabilities` | a readonly array of strings, or omitted entirely | the external reach this noun's own manifest declares. No current noun sets it. Settings > Extensions' reach line reads this field directly, so a future noun's declared capabilities show up there with no other code change. |
 | `fileBacked` | boolean -- REQUIRED, never optional | does this noun's own placed instance read Payload.mirrorPath as a real external file (goal 0232's file-backed preview/open/watch contract)? true gets the shared live-watch subscription (its own content Component sees mirrorVersion bump) and the object.openInDefaultApp context-menu command uniformly, with no extra wiring of either. A noun with no boardObjectKind at all still declares it, always false. |
 | `sticky` | boolean -- REQUIRED, never optional | does this tool stay armed after a completed gesture (pencil/eraser/laser -- repeated strokes/passes are the point), or disarm after one? useAtlasToolGesture.ts reads this to decide whether a gesture's own onEnd may call ctx.disarm/disarmUnlessLocked at all -- a sticky tool gets no-ops for both. A non-drag tool still declares it, always false. |
diff --git a/userdocs/reference/extending-the-canvas.md b/userdocs/reference/extending-the-canvas.md
index 8eea2601..7066da64 100644
--- a/userdocs/reference/extending-the-canvas.md
+++ b/userdocs/reference/extending-the-canvas.md
@@ -85,7 +85,7 @@ are never omissions.
 | `boardNodeType` | 'atlas-note', 'atlas-sticky', 'atlas-group', 'atlas-object', or null | which shared React Flow node component renders this noun's placed instance. null for a tool whose gesture never persists a renderable instance (eraser, laser). |
 | `dragBand` | boolean -- REQUIRED, never optional | only load-bearing when boardNodeType is 'atlas-object': does this noun's own content capture pointer events (a grid, a vendored pan/zoom viewer), so the shared renderer needs to add its own chrome band as the drag surface? A noun whose whole body already drags declares false, not omitted. |
 | `boardObjectKind` | 'shape', 'image', 'ink', 'table', 'diagram', 'sheet', or null | the persisted BoardObject.Kind this noun's own placed instance carries, or null for a tool that never routes through the shared 'atlas-object' renderer. Not always equal to id -- pencil's own placed instance is Kind 'ink' -- so content resolution below keys off this field, read from object.Kind, never off id. |
-| `content` | an object with Component (a React component accepting { object, mirrorVersion }), ariaLabelKey (a string), and role ('img' or undefined) -- or null | this noun's own placed-instance content contribution. registerNoun() feeds it into the board-object content registry (atlasNounRegistry.ts's registerBoardObjectContent) whenever boardObjectKind is non-null, killing AtlasBoardObjectNode.tsx's former per-Kind hand branch. A tool-less noun (diagram) calls registerBoardObjectContent directly instead of declaring this field at all, since it has no AtlasToolShape to satisfy. mirrorVersion bumps on a live disk change to a fileBacked Kind's own mirrored file (see fileBacked below) -- a non-file-backed Component simply ignores it. |
+| `content` | an object with Component (a React component accepting { object, mirrorVersion }), ariaLabelKey (a string), and role ('img' or undefined) -- or null | this noun's own placed-instance content contribution. registerNoun() feeds it into the board-object content registry (atlasNounRegistry.ts's registerBoardObjectContent) whenever boardObjectKind is non-null, killing AtlasBoardObjectNode.tsx's former per-Kind hand branch. A tool-less noun (diagram, sheet) calls registerBoardObjectContent directly instead of declaring this field at all, since it has no AtlasToolShape to satisfy -- it instead sets this same content shape's own optional `extension` member (icon, label, description, disableScopeNote) so Settings > Extensions can still render an honest row for it. mirrorVersion bumps on a live disk change to a fileBacked Kind's own mirrored file (see fileBacked below) -- a non-file-backed Component simply ignores it. |
 | `capabilities` | a readonly array of strings, or omitted entirely | the external reach this noun's own manifest declares. No current noun sets it. Settings > Extensions' reach line reads this field directly, so a future noun's declared capabilities show up there with no other code change. |
 | `fileBacked` | boolean -- REQUIRED, never optional | does this noun's own placed instance read Payload.mirrorPath as a real external file (goal 0232's file-backed preview/open/watch contract)? true gets the shared live-watch subscription (its own content Component sees mirrorVersion bump) and the object.openInDefaultApp context-menu command uniformly, with no extra wiring of either. A noun with no boardObjectKind at all still declares it, always false. |
 | `sticky` | boolean -- REQUIRED, never optional | does this tool stay armed after a completed gesture (pencil/eraser/laser -- repeated strokes/passes are the point), or disarm after one? useAtlasToolGesture.ts reads this to decide whether a gesture's own onEnd may call ctx.disarm/disarmUnlessLocked at all -- a sticky tool gets no-ops for both. A non-drag tool still declares it, always false. |