fix(transcription): harden re-edit pencil hit-testing + disable sync (#628 review)

Addresses the clean-agent review of PR #717:

- C1: the hidden pencil was opacity-0 only, which still hit-tests; its 44px box
  overhangs adjacent text, so a click in the gap between two mentions could land
  on the invisible button and spuriously open the dropdown (AC-8 hole). Add
  pointer-events-none while hidden, re-enabled with the opacity reveal on
  hover/focus.
- C2/N1: editor.setEditable() emits "update", not a ProseMirror transaction, so
  the NodeView's 'transaction' listener missed a mid-session disable flip (stale
  aria-disabled/tabindex; the comment was wrong). Listen on 'update' instead —
  which also skips selection-only changes, so it fires far less often.
- N2: track the node across update() so the pencil opens with the live
  displayName (hardening; relink only swaps personId today).

Tests: structural guard that the hidden pencil is pointer-events-none + reveals,
and a mid-session disable-flip test (fixture gains an onReady setDisabled hook).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/shared/discussion/PersonMentionEditor.svelte.spec.ts

@@ -1333,3 +1333,54 @@ describe('PersonMentionEditor — #628 editing announce', () => {
 		});
 	});
 });
+
+// ─── #628 review fixes: hidden-pencil hit-testing + mid-session disable ───────
+
+describe('PersonMentionEditor — #628 review fixes', () => {
+	it('keeps the hidden pencil out of hit-testing (pointer-events-none until revealed)', async () => {
+		// opacity-0 alone still hit-tests, and the 44px button overhangs adjacent
+		// text — so a click in the gap between mentions would otherwise land on the
+		// invisible pencil and open the dropdown (AC-8). It must be pointer-events-none
+		// while hidden and only become clickable together with the opacity reveal.
+		renderHost({ value: '@Aug ', mentionedPersons: [{ personId: 'p-aug', displayName: 'Aug' }] });
+		await vi.waitFor(() =>
+			expect(document.querySelector('[data-type="mention"] button')).not.toBeNull()
+		);
+		const btn = document.querySelector('[data-type="mention"] button') as HTMLElement;
+		expect(btn.className).toContain('pointer-events-none');
+		expect(btn.className).toContain('group-hover/mention:pointer-events-auto');
+		expect(btn.className).toContain('group-focus-within/mention:pointer-events-auto');
+	});
+
+	it('re-syncs the pencil to inert when the editor is disabled mid-session', async () => {
+		// editor.setEditable() emits "update", not a transaction — the NodeView must
+		// listen on "update" or a runtime disable flip leaves the pencil stale.
+		let setDisabled!: (value: boolean) => void;
+		render(PersonMentionEditorHost, {
+			initialValue: '@Aug ',
+			initialMentions: [{ personId: 'p-aug', displayName: 'Aug' }],
+			disabled: false,
+			onChange: () => {},
+			onReady: (api: { setDisabled: (value: boolean) => void }) => {
+				setDisabled = api.setDisabled;
+			}
+		});
+
+		await vi.waitFor(() => {
+			const btn = document.querySelector(
+				'[data-type="mention"] button'
+			) as HTMLButtonElement | null;
+			expect(btn).not.toBeNull();
+			expect(btn!.disabled).toBe(false);
+		});
+
+		setDisabled(true);
+
+		await vi.waitFor(() => {
+			const btn = document.querySelector('[data-type="mention"] button') as HTMLButtonElement;
+			expect(btn.disabled).toBe(true);
+			expect(btn.getAttribute('aria-disabled')).toBe('true');
+			expect(btn.tabIndex).toBe(-1);
+		});
+	});
+});