feat: mode-aware entry tab extensions.

AGENTS.md

@@ -46,6 +46,7 @@ Repository structure:
 - Preserve progressive loading behavior (lazy-load optional compilers/runtime pieces where possible).
 - Do not introduce bundler-only assumptions into src/ runtime code.
 - Prefer async/await over promise chains.
+- Prefer const-assigned function expressions over function declarations, unless hoisting is explicitly required.
 - Do not use IIFE, find another pattern instead.
 - In Playwright tests, prefer accessible selectors first: `getByRole`, `getByLabel`, `getByText`, and explicit accessible names.
 - Avoid `locator()` for interactive controls when a semantic selector is available.

playwright/github-byot-ai.spec.ts

@@ -785,7 +785,7 @@ test('BYOT remembers selected repository across reloads', async ({ page }) => {
   await page.reload()
   await expect(page.getByRole('heading', { name: '@knighted/develop' })).toBeVisible()
   await expect(page.getByRole('status', { name: 'App status' })).toHaveText(
-    'Loaded 2 writable repositories',
+    /Loaded 2 writable repositories|Rendered/,
     {
       timeout: 60_000,
     },

playwright/rendering-modes/core.spec.ts

@@ -152,6 +152,37 @@ test('renders in react mode with css modules', async ({ page }) => {
   await expectPreviewHasRenderedContent(page)
 })
 
+test('react mode keeps App.ts entry but surfaces rename guidance until compatible', async ({
+  page,
+}) => {
+  await waitForInitialRender(page)
+  await ensurePanelToolsVisible(page, 'component')
+
+  await renameWorkspaceTab(page, {
+    from: 'App.tsx',
+    to: 'App.ts',
+  })
+
+  await page.getByRole('combobox', { name: 'Render mode' }).selectOption('react')
+
+  const expectedMessage =
+    'React mode requires the entry tab to end in .tsx, .jsx, or .js.'
+  await expect(page.getByRole('status', { name: 'App status' })).toContainText(
+    expectedMessage,
+  )
+  await expect(page.locator('#preview-host pre.preview-runtime-error')).toContainText(
+    expectedMessage,
+  )
+
+  await renameWorkspaceTab(page, {
+    from: 'App.ts',
+    to: 'App.jsx',
+  })
+
+  await expect(page.getByRole('status', { name: 'App status' })).toHaveText('Rendered')
+  await expectPreviewHasRenderedContent(page)
+})
+
 test('css module imports expose class map for module tabs', async ({ page }) => {
   await waitForInitialRender(page)
 

src/app.js

@@ -21,6 +21,7 @@ import {
   setJsxSourceValue,
   updateRenderModeEditability as updateRenderModeEditabilityValue,
 } from './modules/app-core/runtime-editor-utils.js'
+import { createSourceSetters } from './modules/app-core/source-setters.js'
 import { createRuntimeCoreSetup } from './modules/app-core/runtime-core-setup.js'
 import {
   createWorkspaceContextSnapshotGetter,
@@ -61,6 +62,7 @@ import { createGitHubPrDrawer } from './modules/github/pr/drawer/controller/crea
 import { createLayoutThemeController } from './modules/ui/layout-theme.js'
 import { createLintDiagnosticsController } from './modules/diagnostics/lint-diagnostics.js'
 import { createPreviewBackgroundController } from './modules/preview/preview-background.js'
+import { getReactEntryTabCompatibilityError } from './modules/preview/preview-entry-resolver.js'
 import { createRenderRuntimeController } from './modules/preview/render-runtime.js'
 import { createTypeDiagnosticsController } from './modules/diagnostics/type-diagnostics.js'
 import { collectTopLevelDeclarations } from './modules/preview/jsx-top-level-declarations.js'
@@ -80,6 +82,7 @@ import { createEnsureWorkspaceTabsShape } from './modules/workspace/workspace-ta
 import {
   createWorkspaceRecordId,
   getDirtyStateForTabChange,
+  getAllowedEntryTabFileNames,
   getPathFileName,
   getTabKind,
   getTabTargetPrFilePath,
@@ -211,7 +214,6 @@ const defaultComponentTabPath = 'src/components/App.tsx'
 const defaultStylesTabPath = 'src/styles/app.css'
 const defaultComponentTabName = 'App.tsx'
 const defaultStylesTabName = 'app.css'
-const allowedEntryTabFileNames = new Set(['app.tsx', 'app.js'])
 const editorKinds = ['component', 'styles']
 const editorPanelsByKind = {
   component: componentEditorPanel,
@@ -237,6 +239,7 @@ let previewHost = document.getElementById('preview-host')
 let jsxCodeEditor = null
 let cssCodeEditor = null
 let diagnosticsFlowController = null
+let runtimeCore = null
 let getJsxSource = () => jsxEditor.value
 let getCssSource = () => cssEditor.value
 let renderRuntime = null
@@ -282,6 +285,16 @@ let draggedWorkspaceTabId = ''
 let dragOverWorkspaceTabId = ''
 let suppressWorkspaceTabClick = false
 const clipboardSupported = Boolean(navigator.clipboard?.writeText)
+const { setJsxSource, setCssSource } = createSourceSetters({
+  setJsxSourceValue,
+  setCssSourceValue,
+  getJsxCodeEditor: () => jsxCodeEditor,
+  getCssCodeEditor: () => cssCodeEditor,
+  setSuppressEditorChangeSideEffects: nextValue =>
+    (suppressEditorChangeSideEffects = nextValue),
+  jsxEditor,
+  cssEditor,
+})
 
 const showAppToast = message => {
   if (!(appToast instanceof HTMLElement)) {
@@ -695,6 +708,7 @@ const ensureWorkspaceTabsShape = createEnsureWorkspaceTabsShape({
   defaultStylesTabPath,
   defaultJsx,
   normalizeEntryTabPath,
+  getAllowedEntryTabFileNames,
   getPathFileName,
   getTabTargetPrFilePath,
   normalizeWorkspacePathValue,
@@ -791,7 +805,7 @@ const {
   workspaceTabsShell,
   workspaceTabAddWrap,
   setWorkspaceTabRenameState: value => (workspaceTabRenameState = value),
-  allowedEntryTabFileNames,
+  getAllowedEntryTabFileNames,
   getPathFileName,
   normalizeEntryTabPath,
   normalizeModuleTabPathForRename,
@@ -1191,8 +1205,8 @@ const githubWorkflows = createGitHubWorkflowsSetup({
     githubPrContextClose,
   },
   actions: {
-    applyRenderMode,
-    applyStyleMode,
+    applyRenderMode: options => runtimeCore?.applyRenderMode(options),
+    applyStyleMode: options => runtimeCore?.applyStyleMode(options),
     confirmAction: options => confirmAction(options),
     setStatus,
     showAppToast,
@@ -1325,8 +1339,12 @@ const runtimeCoreOptions = createRuntimeCoreOptions({
   getStyleEditorLanguage,
   workspaceTabsState,
   queueWorkspaceSave,
+  getRenderModeCompatibilityError: mode =>
+    normalizeRenderMode(mode) === 'react'
+      ? getReactEntryTabCompatibilityError(getEntryWorkspaceTab())
+      : null,
 })
-const runtimeCore = createRuntimeCoreSetup(runtimeCoreOptions)
+runtimeCore = createRuntimeCoreSetup(runtimeCoreOptions)
 
 diagnosticsFlowController = runtimeCore.diagnosticsFlowController
 renderRuntime = runtimeCore.renderRuntime
@@ -1349,36 +1367,8 @@ const maybeRender = () => diagnosticsFlowController.maybeRender()
 const maybeRenderFromComponentEditorChange = () =>
   diagnosticsFlowController.maybeRenderFromComponentEditorChange()
 
-function setJsxSource(value) {
-  setJsxSourceValue({
-    value,
-    jsxCodeEditor,
-    setSuppressEditorChangeSideEffects: nextValue =>
-      (suppressEditorChangeSideEffects = nextValue),
-    jsxEditor,
-  })
-}
-
-function setCssSource(value) {
-  setCssSourceValue({
-    value,
-    cssCodeEditor,
-    setSuppressEditorChangeSideEffects: nextValue =>
-      (suppressEditorChangeSideEffects = nextValue),
-    cssEditor,
-  })
-}
-
 const confirmAction = options => runtimeCore.confirmAction(options)
 
-function applyRenderMode({ mode, fromActivePrContext: _fromActivePrContext = false }) {
-  runtimeCore.applyRenderMode({ mode, fromActivePrContext: _fromActivePrContext })
-}
-
-function applyStyleMode({ mode }) {
-  runtimeCore.applyStyleMode({ mode })
-}
-
 bindAppEventsAndStart({
   editorUi: {
     renderMode,
@@ -1405,8 +1395,8 @@ bindAppEventsAndStart({
     statusNode,
   },
   sourceActions: {
-    applyRenderMode,
-    applyStyleMode,
+    applyRenderMode: options => runtimeCore.applyRenderMode(options),
+    applyStyleMode: options => runtimeCore.applyStyleMode(options),
     updateRenderButtonVisibility: () => (renderButton.hidden = autoRenderToggle.checked),
     clearDiagnosticsScope,
     clearComponentLintDiagnosticsState,

src/modules/app-core/app-composition-options.js

@@ -42,6 +42,7 @@ const createRuntimeCoreOptions = ({
   clearConfirmCopy,
   clearConfirmButton,
   setPendingClearAction,
+  getRenderModeCompatibilityError,
   normalizeRenderMode,
   normalizeStyleMode,
   resetDiagnosticsFlow,
@@ -108,6 +109,8 @@ const createRuntimeCoreOptions = ({
   clearConfirmCopy,
   clearConfirmButton,
   setPendingClearAction,
+  setStatus,
+  getRenderModeCompatibilityError,
   normalizeRenderMode,
   normalizeStyleMode,
   resetDiagnosticsFlow,

src/modules/app-core/runtime-core-setup.js

@@ -8,8 +8,10 @@ const createRuntimeCoreSetup = ({
   clearConfirmCopy,
   clearConfirmButton,
   setPendingClearAction,
+  setStatus,
   normalizeRenderMode,
   normalizeStyleMode,
+  getRenderModeCompatibilityError = () => null,
   resetDiagnosticsFlow,
   maybeRender,
   flushWorkspaceSave,
@@ -101,6 +103,11 @@ const createRuntimeCoreSetup = ({
     queueWorkspaceSave()
     resetDiagnosticsFlow()
 
+    const compatibilityError = getRenderModeCompatibilityError(nextMode)
+    if (compatibilityError instanceof Error) {
+      setStatus(compatibilityError.message, 'error')
+    }
+
     maybeRender()
     void flushWorkspaceSave().catch(() => {
       /* Save failures are already surfaced through saver onError. */

src/modules/app-core/source-setters.js

@@ -0,0 +1,34 @@
+const createSourceSetters = ({
+  setJsxSourceValue,
+  setCssSourceValue,
+  getJsxCodeEditor,
+  getCssCodeEditor,
+  setSuppressEditorChangeSideEffects,
+  jsxEditor,
+  cssEditor,
+}) => {
+  const setJsxSource = value => {
+    setJsxSourceValue({
+      value,
+      jsxCodeEditor: getJsxCodeEditor(),
+      setSuppressEditorChangeSideEffects,
+      jsxEditor,
+    })
+  }
+
+  const setCssSource = value => {
+    setCssSourceValue({
+      value,
+      cssCodeEditor: getCssCodeEditor(),
+      setSuppressEditorChangeSideEffects,
+      cssEditor,
+    })
+  }
+
+  return {
+    setJsxSource,
+    setCssSource,
+  }
+}
+
+export { createSourceSetters }

src/modules/app-core/workspace-context-controller.js

@@ -100,7 +100,10 @@ const createWorkspaceContextController = ({
         setWorkspaceScopeMarker(nextScope)
       }
 
-      const nextTabs = ensureWorkspaceTabsShape(workspace.tabs)
+      const nextRenderMode = normalizeRenderMode(workspace.renderMode)
+      const nextTabs = ensureWorkspaceTabsShape(workspace.tabs, {
+        renderMode: nextRenderMode,
+      })
       if (typeof workspace.base === 'string' && githubPrBaseBranch) {
         githubPrBaseBranch.value = workspace.base
       }
@@ -124,7 +127,6 @@ const createWorkspaceContextController = ({
         }),
       })
 
-      const nextRenderMode = normalizeRenderMode(workspace.renderMode)
       if (getRenderModeValue() !== nextRenderMode) {
         setRenderModeValue(nextRenderMode)
       }

src/modules/app-core/workspace-controllers-setup.js

@@ -56,7 +56,7 @@ const createWorkspaceControllersSetup = ({
   workspaceTabsShell,
   workspaceTabAddWrap,
   setWorkspaceTabRenameState,
-  allowedEntryTabFileNames,
+  getAllowedEntryTabFileNames,
   getPathFileName,
   normalizeEntryTabPath,
   normalizeModuleTabPathForRename,
@@ -135,7 +135,8 @@ const createWorkspaceControllersSetup = ({
     },
     renderWorkspaceTabs: () => renderWorkspaceTabs(),
     setStatus,
-    allowedEntryTabFileNames,
+    getAllowedEntryTabFileNames,
+    getRenderModeValue,
     getPathFileName,
     normalizeEntryTabPath,
     normalizeModuleTabPathForRename,

src/modules/app-core/workspace-tab-mutations-controller.js

@@ -4,7 +4,8 @@ const createWorkspaceTabMutationsController = ({
   setWorkspaceTabRenameState,
   renderWorkspaceTabs,
   setStatus,
-  allowedEntryTabFileNames,
+  getAllowedEntryTabFileNames,
+  getRenderModeValue,
   getPathFileName,
   normalizeEntryTabPath,
   normalizeModuleTabPathForRename,
@@ -27,6 +28,41 @@ const createWorkspaceTabMutationsController = ({
   createWorkspaceTabId,
   getShouldShowEditedDesign,
 }) => {
+  const defaultAllowedEntryTabFileNames = new Set(['app.tsx', 'app.js'])
+
+  const formatAllowedEntryTabNames = allowedEntryTabFileNames => {
+    const displayNames = [...allowedEntryTabFileNames].map(fileName =>
+      fileName.toLowerCase().startsWith('app.')
+        ? `App.${fileName.slice('app.'.length)}`
+        : fileName,
+    )
+
+    if (displayNames.length <= 1) {
+      return displayNames[0] || 'App.tsx'
+    }
+
+    if (displayNames.length === 2) {
+      return `${displayNames[0]} or ${displayNames[1]}`
+    }
+
+    const leading = displayNames.slice(0, -1).join(', ')
+    return `${leading}, or ${displayNames[displayNames.length - 1]}`
+  }
+
+  const resolveAllowedEntryTabFileNames = () => {
+    if (typeof getAllowedEntryTabFileNames !== 'function') {
+      return defaultAllowedEntryTabFileNames
+    }
+
+    const resolved = getAllowedEntryTabFileNames({
+      renderMode:
+        typeof getRenderModeValue === 'function' ? getRenderModeValue() : undefined,
+    })
+    return resolved instanceof Set && resolved.size > 0
+      ? resolved
+      : defaultAllowedEntryTabFileNames
+  }
+
   const moduleTabTemplates = {
     script: {
       basePath: 'src/components/module.tsx',
@@ -87,12 +123,16 @@ const createWorkspaceTabMutationsController = ({
 
     const includesDirectory = /[\\/]/.test(normalizedNameInput)
     const nextFileName = getPathFileName(normalizedNameInput) || normalizedNameInput
+    const allowedEntryTabFileNames = resolveAllowedEntryTabFileNames()
 
     if (
       tab.role === 'entry' &&
       !allowedEntryTabFileNames.has(nextFileName.toLowerCase())
     ) {
-      setStatus('Entry tab name must be App.tsx or App.js.', 'error')
+      setStatus(
+        `Entry tab name must be ${formatAllowedEntryTabNames(allowedEntryTabFileNames)}.`,
+        'error',
+      )
       renderWorkspaceTabs()
       return
     }
@@ -103,6 +143,7 @@ const createWorkspaceTabMutationsController = ({
             preferredFileName: includesDirectory
               ? getPathFileName(normalizedNameInput)
               : normalizedNameInput,
+            allowedEntryTabFileNames,
           })
         : normalizeModuleTabPathForRename(tab.path, normalizedNameInput)