fix(web): re-apply the editor's accessible name, and correct the README's scope

Copilot's third pass generated no new inline comments; all three of its
suppressed ones were right.

- `ariaLabel` is now re-applied from the wiring effect, not only at mount.
  `setOptions` updates Ace's option when the prop changes, but Ace recomputes
  the textarea's `aria-label` from it inside `TextInput.setAriaLabel()`, which
  it calls when the cursor moves — so a name that changed while the editor
  stayed mounted (a tool refreshed in place under a new field title, which
  `SchemaJsonField` passes straight through) left the visible label and the
  accessible name disagreeing until the user clicked into the box. `onLoad`
  keeps doing it too, since an effect runs after paint and this is the
  control's only name.

- The README claimed this editor is on "every surface where JSON is typed or
  displayed", which is false in two places it now names instead:
  `ExperimentalFeaturesPanel`'s JSON-RPC *response* is still a read-only
  `Textarea` (only its request box moved), and `OAuthTokenField` renders a
  decoded JWT in a `Code` block beside the raw token. Both bypass
  `ContentViewer` and so are not reached by its JSON branch. Documenting them
  as exceptions is what keeps the section from sending a maintainer to the
  wrong abstraction.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UL9retfvAXRgvi6EWk4SY4
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/components/elements/JsonEditor/JsonEditor.test.tsx

@@ -36,6 +36,25 @@ describe("JsonEditor", () => {
     expect(screen.getByLabelText(aceLabel(LABEL))).toBeInTheDocument();
   });
 
+  // Ace recomputes the textarea's `aria-label` from its option only when the
+  // cursor moves, so a name that changes while the editor stays mounted — a
+  // tool refreshed in place under a new field title — would leave the visible
+  // label and the accessible name disagreeing until the user clicked into it.
+  it("re-applies the accessible name when it changes in place", () => {
+    const { rerender } = renderWithMantine(
+      <JsonEditor ariaLabel="Series JSON" value="" onChange={vi.fn()} />,
+    );
+    expect(screen.getByLabelText(aceLabel("Series JSON"))).toBeInTheDocument();
+
+    rerender(
+      <JsonEditor ariaLabel="Data points JSON" value="" onChange={vi.fn()} />,
+    );
+    expect(
+      screen.getByLabelText(aceLabel("Data points JSON")),
+    ).toBeInTheDocument();
+    expect(screen.queryByLabelText(aceLabel("Series JSON"))).toBeNull();
+  });
+
   it("shows the text it is given, verbatim", () => {
     // Braces, not a bare JSX string: a JSX string attribute does not process
     // escapes, so `'…\n…'` written inline would be a literal backslash-n.

clients/web/src/components/elements/JsonEditor/JsonEditor.tsx

@@ -149,12 +149,28 @@ export function JsonEditor({
   // wrapper's own id is what makes the `<label for>` focus the editor; the
   // error wiring follows Mantine's `${id}-error` naming.
   useEffect(() => {
-    const element = editorRef.current?.textInput.getElement();
+    const editor = editorRef.current;
+    const element = editor?.textInput.getElement();
     /* v8 ignore next -- the ref is set in `onLoad`, which react-ace calls
        synchronously on mount, so this effect always sees an element. */
-    if (!element) return;
+    if (!editor || !element) return;
     element.id = wrapperId;
 
+    // Re-apply the accessible name, not just set it once at mount.
+    //
+    // `setOptions` does update Ace's *option* when `ariaLabel` changes, but Ace
+    // only recomputes the textarea's `aria-label` from it inside
+    // `TextInput.setAriaLabel()`, which it calls when the cursor moves. So a
+    // name that changes while the editor stays mounted — a tool refreshed in
+    // place under a new field title, which `SchemaJsonField` passes straight
+    // through — leaves the visible label and the accessible name disagreeing
+    // until the user happens to click into the box.
+    //
+    // `onLoad` still does this too: an effect runs after paint, and this is the
+    // control's only name, so mount should not present a frame without it.
+    editor.setOption("textInputAriaLabel", ariaLabel);
+    editor.textInput.setAriaLabel();
+
     // Both the description and the error are rendered by the wrapper and both
     // describe this control, so both ids belong here — a supplied description
     // is otherwise never announced, and it must not be dropped just because the
@@ -197,7 +213,7 @@ export function JsonEditor({
       element.removeAttribute("aria-disabled");
       element.tabIndex = 0;
     }
-  }, [wrapperId, hasError, description, disabled]);
+  }, [wrapperId, hasError, description, disabled, ariaLabel]);
 
   return (
     <Input.Wrapper