fix: every registered extension appears -- the list derives from nouns, not tray tools (goal 0237)

Settings > Extensions was built off ATLAS_TOOLS (tray tools only), so
diagram and sheet -- both file-drop-only nouns with no tray identity --
were invisible even though they're fully registered canvas nouns.

The list now derives from every registered noun: tray tools plus
tool-less nouns (diagram, sheet), normalized into one ExtensionRowSource
shape (extensionMeta.ts) so ExtensionRow.tsx never branches on which
kind of noun it's rendering. Diagram and sheet declare their own
icon/label/description/disableScopeNote via a new optional `extension`
field on AtlasNounContent, read back by atlasNounRegistry.ts's
toolLessNounExtensions().

Disabling a tool-less noun has no tray button to remove, so its row
states the honest, narrower scope: it gates useAtlasNativeFileDrop.ts's
own drop routing (extracted into the pure, testable resolveFileDropKind)
and, for diagram, dispatchObjectEdit's embedded-engine door (already
keyed off object.Kind since goal 0244).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012im1JxQQV2ahnXzZDdVmZq

Author: alicoding

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()

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",

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

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.',
+  },
 })

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.',
+  },
 })

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')
+  })
+})