feat: frontend turn_html_replace SSE handler for regenerate live-swap (T86)

tests/test_render.py

@@ -85,3 +85,26 @@ def test_render_prose_mixed_full_message():
     assert '<em class="action">looks up</em>' in out
     # The apostrophe in ``she's`` is HTML-escaped to ``&#x27;``.
     assert '<span class="ooc">((she&#x27;s tired))</span>' in out
+
+
+def test_render_turn_html_stamps_event_id_when_provided():
+    """T86 follow-up: when ``event_id`` is supplied the wrapper DIV
+    carries ``id="turn-<event_id>"`` so the chat-page
+    ``turn_html_replace`` SSE handler can locate the prior turn DOM
+    node by id and swap it in-place. Without the id the handler's
+    ``getElementById('turn-' + supersedes_id)`` lookup misses and
+    the regenerated turn appends instead of replaces.
+    """
+    out = render_turn_html("BotA", "Hello.", role="bot", event_id=42)
+    assert 'id="turn-42"' in out
+    # The id must sit on the wrapper DIV, not somewhere nested inside.
+    assert out.startswith('<div id="turn-42" class="turn turn-bot">')
+
+
+def test_render_turn_html_omits_id_when_event_id_missing():
+    """Legacy callers (no ``event_id`` passed) get a clean DIV with no
+    id attribute — preserves the pre-T86 fragment shape.
+    """
+    out = render_turn_html("BotA", "Hello.", role="bot")
+    assert "id=" not in out
+    assert out.startswith('<div class="turn turn-bot">')