plan(textarea-editor): consolidate Task 4 editor.js into one block

The plan had Step 1 (initial widget) + Step 2 (setLanguage patch); the
implementation merges them into one final file. Update the plan to
show the final file verbatim so a future regeneration produces the
same output. Step 2 in the plan is renumbered to 'Manual verification
note' (just the deferred-to-Task-6 sentence) for completeness.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/superpowers/plans/2026-05-16-textarea-code-editor.md

@@ -387,12 +387,19 @@ variables where present so the editor matches the site palette."
 **Files:**
 - Create: `l4d2web/l4d2web/static/js/editor.js`
 
-The widget mounts on every `<textarea data-editor-language>`, hides the textarea, creates a sibling contenteditable, mounts CodeJar with Prism highlighting, and pipes content back to the textarea on every input. Autocomplete is added in Task 8; this task lands a working "highlight as you type" experience.
+The widget mounts on every `<textarea data-editor-language>`, hides the textarea, creates a sibling contenteditable, mounts CodeJar with Prism highlighting, and pipes content back to the textarea on every input. Autocomplete is added in Task 9; this task lands a working "highlight as you type" experience.
 
-- [ ] **Step 1: Write the widget skeleton**
+- [x] **Step 1: Write `editor.js` (consolidated final version)**
 
 Create `l4d2web/l4d2web/static/js/editor.js`:
 
+Key design decisions baked into the final file (both the initial skeleton and the `setLanguage` fix merged into one):
+
+- `findFilenameInput` is hoisted above `mount` so the initial `language` resolution can reference it without a forward-reference hazard.
+- `attachOnUpdate(jarInstance)` is a small helper called at construction time AND inside `setLanguage`'s remount, avoiding a duplicated callback body.
+- All method bodies in `instance` use `instance.jar` (not the captured `jar` variable) so `setValue`/`getValue`/`destroy` always operate on the *current* jar after a `setLanguage` swap.
+- `setLanguage` uses tear-down-and-remount (not `updateOptions`/`code.__highlighter`) because CodeJar captures its highlight callback by closure at construction time and provides no API to swap it on a live instance.
+
 ```js
 // Code editor widget. Mounts on any <textarea data-editor-language>.
 // The textarea stays in the DOM (display:none) and the widget mirrors
@@ -433,6 +440,14 @@ Create `l4d2web/l4d2web/static/js/editor.js`:
     };
   }
 
+  // For "auto" language: look for a filename input near the textarea
+  // (the files-editor modal). Returns the <input> or null.
+  function findFilenameInput(textarea) {
+    const modal = textarea.closest("dialog, .modal, body");
+    if (!modal) return null;
+    return modal.querySelector(".files-editor-filename");
+  }
+
   function mount(textarea) {
     if (textarea._codeEditor) return textarea._codeEditor;
 
@@ -458,12 +473,16 @@ Create `l4d2web/l4d2web/static/js/editor.js`:
     // on each input while preserving caret position.
     const jar = window.CodeJar(code, highlightFor(language), { tab: "  " });
 
-    jar.onUpdate(function (value) {
+    function attachOnUpdate(jarInstance) {
+      jarInstance.onUpdate(function (value) {
         // Mirror back to the underlying textarea so form POST and any
         // .value readers see the current content.
         textarea.value = value;
         textarea.dispatchEvent(new Event("input", { bubbles: true }));
       });
+    }
+
+    attachOnUpdate(jar);
 
     const instance = {
       textarea,
@@ -472,11 +491,11 @@ Create `l4d2web/l4d2web/static/js/editor.js`:
       jar,
       language,
       setValue: function (text) {
-        jar.updateCode(text);
+        instance.jar.updateCode(text);
         textarea.value = text;
       },
       getValue: function () {
-        return jar.toString();
+        return instance.jar.toString();
       },
       setLanguage: function (name) {
         const next =
@@ -484,17 +503,21 @@ Create `l4d2web/l4d2web/static/js/editor.js`:
             ? resolveAutoLanguage(findFilenameInput(textarea)?.value)
             : name;
         if (next === instance.language) return;
+        // CodeJar captures its highlight callback by closure at
+        // construction time — there is no API to swap it on a live
+        // instance. Tear down and remount with the new highlighter.
+        // Caret position is lost on switch; acceptable since this is
+        // triggered by the user clicking the language dropdown.
+        const currentText = instance.jar.toString();
+        instance.jar.destroy();
         instance.language = next;
         code.className = "editor-code language-" + next;
-        jar.updateOptions({});
+        code.textContent = currentText;
-        // Replace the highlighter by recreating it via updateCode (CodeJar
+        instance.jar = window.CodeJar(code, highlightFor(next), { tab: "  " });
-        // doesn't expose setHighlight directly).
+        attachOnUpdate(instance.jar);
-        // Trick: stash the new highlighter on the closure and rerun.
-        code.__highlighter = highlightFor(next);
-        code.__highlighter(code);
       },
       destroy: function () {
-        jar.destroy();
+        instance.jar.destroy();
         shell.remove();
         textarea.style.display = "";
         delete textarea._codeEditor;
@@ -505,14 +528,6 @@ Create `l4d2web/l4d2web/static/js/editor.js`:
     return instance;
   }
 
-  // For "auto" language: look for a filename input near the textarea
-  // (the files-editor modal). Returns the <input> or null.
-  function findFilenameInput(textarea) {
-    const modal = textarea.closest("dialog, .modal, body");
-    if (!modal) return null;
-    return modal.querySelector(".files-editor-filename");
-  }
-
   function mountAll(root) {
     const scope = root || document;
     scope.querySelectorAll("textarea[data-editor-language]").forEach(mount);
@@ -526,52 +541,16 @@ Create `l4d2web/l4d2web/static/js/editor.js`:
     mountAll(document);
   }
 
-  // Re-export for callers that need to mount editors created later (e.g.
+  // Re-export for callers that need to mount editors created later
-  // the files-editor modal which is in the static DOM but only used after
+  // (the files-editor modal exists in the static DOM but is only
-  // user interaction — the initial mount is still correct, but exposing
+  // shown after user interaction — initial mount is correct, but
-  // this hook lets future code mount dynamically-inserted editors).
+  // exposing this hook lets future code mount dynamically-inserted
+  // editors if needed).
   window.l4d2Editor = { mount, mountAll };
 })();
 ```
 
-- [ ] **Step 2: Patch the `setLanguage` hot-path**
+- **Manual verification note:** No smoke test in this task — first live render happens in Task 6 when the blueprint config textarea gets `data-editor-language="srccfg"` and the asset partial is included.
-
-CodeJar's `updateOptions` API doesn't replace the highlighter function — the constructor captured it by closure. Reading the source: CodeJar stores the highlight callback as `highlight` in its options, then calls it on every input. We need a workaround:
-
-Replace the `setLanguage` body with a tear-down-and-remount strategy that preserves caret if possible (for our use case — switching from srccfg to bash in the files-editor — losing caret is acceptable since the user just clicked a dropdown):
-
-```js
-setLanguage: function (name) {
-  const next =
-    name === "auto"
-      ? resolveAutoLanguage(findFilenameInput(textarea)?.value)
-      : name;
-  if (next === instance.language) return;
-  const currentText = jar.toString();
-  jar.destroy();
-  instance.language = next;
-  code.className = "editor-code language-" + next;
-  code.textContent = currentText;
-  instance.jar = window.CodeJar(code, highlightFor(next), { tab: "  " });
-  instance.jar.onUpdate(function (value) {
-    textarea.value = value;
-    textarea.dispatchEvent(new Event("input", { bubbles: true }));
-  });
-},
-```
-
-- [ ] **Step 3: Commit (no test yet — manual smoke runs after Task 6)**
-
-```bash
-git add l4d2web/l4d2web/static/js/editor.js
-git commit -m "feat(editor): widget core — mount, sync, language switch
-
-Mounts on <textarea data-editor-language>, hides the textarea, renders
-content in a contenteditable sibling with Prism highlighting via
-CodeJar. Mirrors content back to textarea.value on every input so form
-POST and existing JS readers keep working unchanged. Exposes
-setValue/setLanguage/getValue on textarea._codeEditor for callers."
-```
 
 ---