feat(editor): overlay code-block controls, hide language selector until hover (closes #275)

The code-block control panel (language selector + copy) took a full row above
the code. Move both to an absolute overlay in the top-right corner and hide the
language selector until the block is hovered/focused; the copy button stays
always visible. In read-only the language selector isn't rendered at all. The
<pre> (editable contentDOM) stays FIRST in the DOM so click hit-testing (#146)
is not regressed; the panel leaves the flow via position:absolute.

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

apps/client/src/features/editor/components/code-block/code-block-view.tsx

@@ -50,10 +50,10 @@ export default function CodeBlockView(props: NodeViewProps) {
       {/* #146: the editable <pre><code> (contentDOM) MUST come first in the DOM.
           With the non-editable menu rendered before it, the browser's click
           hit-testing snapped the caret up one line. Render content first; the
-          menu is rendered after it and lifted back above visually via flex
+          menu is rendered after it and floated into the top-right corner as an
-          `order: -1` (the `.codeBlock` wrapper is a flex column — see
+          absolute overlay (see `.menuGroup` in code-block.module.css, anchored
-          code-block.module.css). It stays fully in flow as a full-width row
+          to the `position: relative` `.codeBlock` wrapper in code.css). It no
-          above the code: no overlay/absolute positioning. The second #146
+          longer takes a full-width row above the code. The second #146
           mitigation lives in editor-paste-handler.tsx (reflowAfterPaste). */}
       <pre
         spellCheck="false"
@@ -72,17 +72,22 @@ export default function CodeBlockView(props: NodeViewProps) {
         contentEditable={false}
         className={classes.menuGroup}
       >
-        <Select
+        {/* In read-only (published) there is no language selector at all —
-          placeholder="auto"
+            only the copy button. When editable the selector is hidden until
-          checkIconPosition="right"
+            the block is hovered/focused (or its dropdown is open) via the
-          data={extension.options.lowlight.listLanguages().sort()}
+            `.languageSelect` class (see code-block.module.css). */}
-          value={languageValue}
+        {editor.isEditable && (
-          onChange={changeLanguage}
+          <Select
-          searchable
+            placeholder="auto"
-          style={{ maxWidth: "130px" }}
+            checkIconPosition="right"
-          classNames={{ input: classes.selectInput }}
+            data={extension.options.lowlight.listLanguages().sort()}
-          disabled={!editor.isEditable}
+            value={languageValue}
-        />
+            onChange={changeLanguage}
+            searchable
+            style={{ maxWidth: "130px" }}
+            classNames={{ root: classes.languageSelect, input: classes.selectInput }}
+          />
+        )}
 
         <CopyButton value={node?.textContent} timeout={2000}>
           {({ copied, copy }) => (

apps/client/src/features/editor/components/code-block/code-block.module.css

@@ -17,15 +17,37 @@
     justify-content: center;
 }
 
-/* #146: the menu now follows the <pre> in the DOM (so the editable contentDOM is
+/* #146: the menu follows the <pre> in the DOM (so the editable contentDOM is
-   FIRST and click hit-testing is correct). Lift it back ABOVE the code visually
+   FIRST and click hit-testing is correct). Instead of sitting in-flow, it is
-   with flex `order` — the .codeBlock wrapper is a flex column (see code.css) —
+   floated into the top-right corner as an absolute overlay anchored to the
-   so the menu still reads as a row above the code, exactly as before, without
+   `position: relative` .codeBlock wrapper (see code.css), so it no longer
-   sitting in-flow before the contentDOM. */
+   takes a full-width row above the code. The Mantine dropdown is portaled, so
+   it is never clipped by the overlay. */
 .menuGroup {
-    order: -1;
+    position: absolute;
+    top: 8px;
+    right: 8px;
+    z-index: 1;
+    gap: 4px;
 
     @media print {
         display: none;
     }
 }
+
+/* The language selector is hidden until the block is hovered, or the selector
+   itself is focused / its dropdown is open. It keeps its width in the flex
+   Group (only opacity toggles) so the copy button never jumps, and
+   `pointer-events: none` while hidden lets clicks fall through to the code.
+   `.codeBlock` is the global NodeViewWrapper class → use :global(). */
+.languageSelect {
+    opacity: 0;
+    pointer-events: none;
+    transition: opacity 150ms ease;
+}
+
+:global(.codeBlock):hover .languageSelect,
+.languageSelect:focus-within {
+    opacity: 1;
+    pointer-events: auto;
+}

apps/client/src/features/editor/styles/code.css

@@ -1,9 +1,12 @@
 .ProseMirror {
   .codeBlock {
-    /* #146: flex column so the menu (rendered AFTER <pre> in the DOM, so the
+    /* #146: flex column keeps the editable <pre> (first in the DOM so click
-       editable contentDOM is first) is lifted back above the code via `order`. */
+       hit-testing is correct) laid out above any Mermaid diagram. `position:
+       relative` anchors the control panel, which is floated into the top-right
+       corner as an absolute overlay (see `.menuGroup` in code-block.module.css). */
     display: flex;
     flex-direction: column;
+    position: relative;
     padding: 4px;
     border-radius: var(--mantine-radius-default);
     background-color: light-dark(var(--mantine-color-gray-0),  var(--mantine-color-dark-8));