fix(codemirror): decoration-unfilled returns [] not Decoration.none (G5 runtime crash)

makeDecorationExt returned Decoration.none (a DecorationSet/RangeSet, NOT an
Extension) when the decoration slot was unfilled. Placed in the extensions array
via decorationCompartment.of(...), it made EditorState.create throw at runtime —
the editor never mounted, so ALL 6 CodeMirrorScreenshot VR cells timed out waiting
for .cm-content. The gutter branch already returned [] correctly. Build/typecheck
passed (CM facet types are loose); only the browser/VR surfaced it — the
build-green != runtime-green gap. Return [] to match the gutter unfilled branch.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: serpentblade

packages/ui/codemirror/packages/angular/src/CodeMirror.ts

@@ -598,7 +598,12 @@ export class CodeMirror {
     // The WidgetType class captures $portals.decoration, so it is defined inside
     // this $onMount-invoked factory (the bundled-leaf typecheck discipline).
     const makeDecorationExt = (dv: any) => {
-      if (!(this.decorationTpl ?? this.templates()?.['decoration'])) return Decoration.none;
+      // Unfilled slot → EMPTY EXTENSION (`[]`), NOT `Decoration.none`. The latter
+      // is a DecorationSet (a RangeSet), which is NOT a valid Extension; placing it
+      // in the extensions array (via `decorationCompartment.of(...)`) makes
+      // EditorState.create throw at runtime — the editor never mounts. Only the
+      // browser surfaces this (CM's facet types are loose, so build/typecheck pass).
+      if (!(this.decorationTpl ?? this.templates()?.['decoration'])) return [];
       // The WidgetType subclass is declared inline (WidgetType REQUIRES subclassing)
       // but its per-widget state (`from`/`to`, the live portal handle) lives in
       // CLOSURE — `makeWidget(from, to)` captures them — NOT in `this` fields, for

packages/ui/codemirror/packages/lit/src/CodeMirror.ts

@@ -582,7 +582,12 @@ private _portalContainers = new Set<HTMLElement>();
     // The WidgetType class captures $portals.decoration, so it is defined inside
     // this $onMount-invoked factory (the bundled-leaf typecheck discipline).
     const makeDecorationExt = (dv: any) => {
-      if (!(this.decoration !== undefined)) return Decoration.none;
+      // Unfilled slot → EMPTY EXTENSION (`[]`), NOT `Decoration.none`. The latter
+      // is a DecorationSet (a RangeSet), which is NOT a valid Extension; placing it
+      // in the extensions array (via `decorationCompartment.of(...)`) makes
+      // EditorState.create throw at runtime — the editor never mounts. Only the
+      // browser surfaces this (CM's facet types are loose, so build/typecheck pass).
+      if (!(this.decoration !== undefined)) return [];
       // The WidgetType subclass is declared inline (WidgetType REQUIRES subclassing)
       // but its per-widget state (`from`/`to`, the live portal handle) lives in
       // CLOSURE — `makeWidget(from, to)` captures them — NOT in `this` fields, for

packages/ui/codemirror/packages/react/src/CodeMirror.tsx

@@ -551,7 +551,12 @@ const CodeMirror = forwardRef<CodeMirrorHandle, CodeMirrorProps>(function CodeMi
     // The WidgetType class captures $portals.decoration, so it is defined inside
     // this $onMount-invoked factory (the bundled-leaf typecheck discipline).
     const makeDecorationExt = (dv: any) => {
-      if (!(props.renderDecoration ?? props.slots?.["decoration"])) return Decoration.none;
+      // Unfilled slot → EMPTY EXTENSION (`[]`), NOT `Decoration.none`. The latter
+      // is a DecorationSet (a RangeSet), which is NOT a valid Extension; placing it
+      // in the extensions array (via `decorationCompartment.of(...)`) makes
+      // EditorState.create throw at runtime — the editor never mounts. Only the
+      // browser surfaces this (CM's facet types are loose, so build/typecheck pass).
+      if (!(props.renderDecoration ?? props.slots?.["decoration"])) return [];
       // The WidgetType subclass is declared inline (WidgetType REQUIRES subclassing)
       // but its per-widget state (`from`/`to`, the live portal handle) lives in
       // CLOSURE — `makeWidget(from, to)` captures them — NOT in `this` fields, for

packages/ui/codemirror/packages/solid/src/CodeMirror.tsx

@@ -444,7 +444,12 @@ export default function CodeMirror(_props: CodeMirrorProps): JSX.Element {
     // The WidgetType class captures $portals.decoration, so it is defined inside
     // this $onMount-invoked factory (the bundled-leaf typecheck discipline).
     const makeDecorationExt = (dv: any) => {
-      if (!(_props.decorationSlot ?? _props.slots?.["decoration"])) return Decoration.none;
+      // Unfilled slot → EMPTY EXTENSION (`[]`), NOT `Decoration.none`. The latter
+      // is a DecorationSet (a RangeSet), which is NOT a valid Extension; placing it
+      // in the extensions array (via `decorationCompartment.of(...)`) makes
+      // EditorState.create throw at runtime — the editor never mounts. Only the
+      // browser surfaces this (CM's facet types are loose, so build/typecheck pass).
+      if (!(_props.decorationSlot ?? _props.slots?.["decoration"])) return [];
       // The WidgetType subclass is declared inline (WidgetType REQUIRES subclassing)
       // but its per-widget state (`from`/`to`, the live portal handle) lives in
       // CLOSURE — `makeWidget(from, to)` captures them — NOT in `this` fields, for

packages/ui/codemirror/packages/svelte/src/CodeMirror.svelte

@@ -634,7 +634,12 @@ onMount(() => {
   // The WidgetType class captures $portals.decoration, so it is defined inside
   // this $onMount-invoked factory (the bundled-leaf typecheck discipline).
   const makeDecorationExt = (dv: any) => {
-    if (!decoration) return Decoration.none;
+    // Unfilled slot → EMPTY EXTENSION (`[]`), NOT `Decoration.none`. The latter
+    // is a DecorationSet (a RangeSet), which is NOT a valid Extension; placing it
+    // in the extensions array (via `decorationCompartment.of(...)`) makes
+    // EditorState.create throw at runtime — the editor never mounts. Only the
+    // browser surfaces this (CM's facet types are loose, so build/typecheck pass).
+    if (!decoration) return [];
     // The WidgetType subclass is declared inline (WidgetType REQUIRES subclassing)
     // but its per-widget state (`from`/`to`, the live portal handle) lives in
     // CLOSURE — `makeWidget(from, to)` captures them — NOT in `this` fields, for

packages/ui/codemirror/packages/vue/src/CodeMirror.vue

@@ -623,7 +623,12 @@ onMounted(() => {
   // The WidgetType class captures $portals.decoration, so it is defined inside
   // this $onMount-invoked factory (the bundled-leaf typecheck discipline).
   const makeDecorationExt = (dv: any) => {
-    if (!slots.decoration) return Decoration.none;
+    // Unfilled slot → EMPTY EXTENSION (`[]`), NOT `Decoration.none`. The latter
+    // is a DecorationSet (a RangeSet), which is NOT a valid Extension; placing it
+    // in the extensions array (via `decorationCompartment.of(...)`) makes
+    // EditorState.create throw at runtime — the editor never mounts. Only the
+    // browser surfaces this (CM's facet types are loose, so build/typecheck pass).
+    if (!slots.decoration) return [];
     // The WidgetType subclass is declared inline (WidgetType REQUIRES subclassing)
     // but its per-widget state (`from`/`to`, the live portal handle) lives in
     // CLOSURE — `makeWidget(from, to)` captures them — NOT in `this` fields, for

packages/ui/codemirror/src/CodeMirror.rozie

@@ -396,7 +396,12 @@ $onMount(() => {
   // The WidgetType class captures $portals.decoration, so it is defined inside
   // this $onMount-invoked factory (the bundled-leaf typecheck discipline).
   const makeDecorationExt = (dv) => {
-    if (!$slots.decoration) return Decoration.none
+    // Unfilled slot → EMPTY EXTENSION (`[]`), NOT `Decoration.none`. The latter
+    // is a DecorationSet (a RangeSet), which is NOT a valid Extension; placing it
+    // in the extensions array (via `decorationCompartment.of(...)`) makes
+    // EditorState.create throw at runtime — the editor never mounts. Only the
+    // browser surfaces this (CM's facet types are loose, so build/typecheck pass).
+    if (!$slots.decoration) return []
     // The WidgetType subclass is declared inline (WidgetType REQUIRES subclassing)
     // but its per-widget state (`from`/`to`, the live portal handle) lives in
     // CLOSURE — `makeWidget(from, to)` captures them — NOT in `this` fields, for