diff --git a/apps/client/src/features/editor/components/code-block/code-block-view.test.tsx b/apps/client/src/features/editor/components/code-block/code-block-view.test.tsx
new file mode 100644
index 00000000..0048b45c
--- /dev/null
+++ b/apps/client/src/features/editor/components/code-block/code-block-view.test.tsx
@@ -0,0 +1,68 @@
+import { describe, it, expect, vi } from "vitest";
+import { render } from "@testing-library/react";
+
+// Covers the read-only render branch (PR #278): the language <Select> renders
+// only when `editor.isEditable`; in read-only the copy button still shows.
+// Mocks mirror the #146 structural harness (footnote-views.structure.test.tsx),
+// except Select becomes a detectable node so we can assert its presence/absence.
+vi.mock("@tiptap/react", () => ({
+  NodeViewWrapper: ({ children }: any) => <div>{children}</div>,
+  NodeViewContent: (props: any) => <div data-node-view-content="" {...props} />,
+}));
+vi.mock("react-i18next", () => ({
+  useTranslation: () => ({ t: (key: string) => key }),
+}));
+vi.mock("@mantine/core", () => ({
+  Group: ({ children }: any) => <div>{children}</div>,
+  Select: () => <div data-testid="language-select" />,
+  Tooltip: ({ children }: any) => <>{children}</>,
+  ActionIcon: ({ children, onClick }: any) => (
+    <button data-testid="copy-button" onClick={onClick}>
+      {children}
+    </button>
+  ),
+}));
+vi.mock("@/components/common/copy-button", () => ({
+  CopyButton: ({ children }: any) => children({ copied: false, copy: () => {} }),
+}));
+vi.mock("@tabler/icons-react", () => ({
+  IconCheck: () => null,
+  IconCopy: () => null,
+}));
+vi.mock("@/features/editor/components/code-block/mermaid-view.tsx", () => ({
+  default: () => null,
+}));
+
+import CodeBlockView from "./code-block-view";
+
+const makeProps = (isEditable: boolean) =>
+  ({
+    node: { attrs: { language: "javascript" }, textContent: "", nodeSize: 1 },
+    editor: {
+      state: { selection: { from: 0, to: 0 } },
+      isEditable,
+      commands: {},
+      on: vi.fn(),
+      off: vi.fn(),
+    },
+    extension: {
+      options: { lowlight: { listLanguages: () => ["javascript", "python"] } },
+    },
+    getPos: () => 0,
+    updateAttributes: () => {},
+    deleteNode: () => {},
+  }) as any;
+
+describe("CodeBlockView language selector visibility (#278)", () => {
+  it("renders the language selector when the editor is editable", () => {
+    const { queryByTestId } = render(<CodeBlockView {...makeProps(true)} />);
+    expect(queryByTestId("language-select")).not.toBeNull();
+    expect(queryByTestId("copy-button")).not.toBeNull();
+  });
+
+  it("hides the language selector in read-only but keeps the copy button", () => {
+    const { queryByTestId } = render(<CodeBlockView {...makeProps(false)} />);
+    expect(queryByTestId("language-select")).toBeNull();
+    expect(queryByTestId("copy-button")).not.toBeNull();
+  });
+});
diff --git a/apps/client/src/features/editor/components/code-block/code-block-view.tsx b/apps/client/src/features/editor/components/code-block/code-block-view.tsx
index 1930f182..3f06d9f9 100644
--- a/apps/client/src/features/editor/components/code-block/code-block-view.tsx
+++ b/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
-          `order: -1` (the `.codeBlock` wrapper is a flex column — see
-          code-block.module.css). It stays fully in flow as a full-width row
-          above the code: no overlay/absolute positioning. The second #146
+          menu is rendered after it and floated into the top-right corner as an
+          absolute overlay (see `.menuGroup` in code-block.module.css, anchored
+          to the `position: relative` `.codeBlock` wrapper in code.css). It no
+          longer takes a full-width row above the code. The second #146
           mitigation lives in editor-paste-handler.tsx (reflowAfterPaste). */}
       <pre
         spellCheck="false"
@@ -67,22 +67,23 @@ export default function CodeBlockView(props: NodeViewProps) {
         <NodeViewContent as="code" className={`language-${language}`} />
       </pre>
 
-      <Group
-        justify="flex-end"
-        contentEditable={false}
-        className={classes.menuGroup}
-      >
-        <Select
-          placeholder="auto"
-          checkIconPosition="right"
-          data={extension.options.lowlight.listLanguages().sort()}
-          value={languageValue}
-          onChange={changeLanguage}
-          searchable
-          style={{ maxWidth: "130px" }}
-          classNames={{ input: classes.selectInput }}
-          disabled={!editor.isEditable}
-        />
+      <Group contentEditable={false} className={classes.menuGroup}>
+        {/* In read-only (published) there is no language selector at all —
+            only the copy button. When editable the selector is hidden until
+            the block is hovered/focused (or its dropdown is open) via the
+            `.languageSelect` class (see code-block.module.css). */}
+        {editor.isEditable && (
+          <Select
+            placeholder="auto"
+            checkIconPosition="right"
+            data={extension.options.lowlight.listLanguages().sort()}
+            value={languageValue}
+            onChange={changeLanguage}
+            searchable
+            style={{ maxWidth: "130px" }}
+            classNames={{ root: classes.languageSelect, input: classes.selectInput }}
+          />
+        )}
 
         <CopyButton value={node?.textContent} timeout={2000}>
           {({ copied, copy }) => (
diff --git a/apps/client/src/features/editor/components/code-block/code-block.module.css b/apps/client/src/features/editor/components/code-block/code-block.module.css
index 4ecda370..e2cb6faf 100644
--- a/apps/client/src/features/editor/components/code-block/code-block.module.css
+++ b/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
-   FIRST and click hit-testing is correct). Lift it back ABOVE the code visually
-   with flex `order` — the .codeBlock wrapper is a flex column (see code.css) —
-   so the menu still reads as a row above the code, exactly as before, without
-   sitting in-flow before the contentDOM. */
+/* #146: the menu follows the <pre> in the DOM (so the editable contentDOM is
+   FIRST and click hit-testing is correct). Instead of sitting in-flow, it is
+   floated into the top-right corner as an absolute overlay anchored to the
+   `position: relative` .codeBlock wrapper (see code.css), so it no longer
+   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;
+}
diff --git a/apps/client/src/features/editor/styles/code.css b/apps/client/src/features/editor/styles/code.css
index 100e4153..9aa1cdab 100644
--- a/apps/client/src/features/editor/styles/code.css
+++ b/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
-       editable contentDOM is first) is lifted back above the code via `order`. */
+    /* #146: flex column keeps the editable <pre> (first in the DOM so click
+       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));