fix document preview refresh after AI edits (#2259)

tests/test_document_ai_preview_refresh_js.py

@@ -0,0 +1,53 @@
+"""Regression guards for AI document updates while Markdown Preview is visible (#2182)."""
+
+import re
+from pathlib import Path
+
+
+SRC = Path(__file__).resolve().parent.parent / "static/js/document.js"
+
+
+def _function_body(name: str) -> str:
+    text = SRC.read_text(encoding="utf-8")
+    match = re.search(rf"\n\s*(?:export\s+)?(?:async\s+)?function\s+{name}\([^)]*\)\s*\{{", text)
+    assert match, f"{name} not found"
+
+    start = match.end()
+    depth = 1
+    i = start
+    while i < len(text) and depth:
+        if text[i] == "{":
+            depth += 1
+        elif text[i] == "}":
+            depth -= 1
+        i += 1
+    assert depth == 0, f"{name} body did not close"
+    return text[start : i - 1]
+
+
+def test_markdown_preview_refresh_rerenders_visible_preview():
+    body = _function_body("_refreshMarkdownPreviewIfVisible")
+
+    assert "_isMarkdownPreviewVisible()" in body
+    assert "lang !== 'markdown'" in body
+    assert "textarea.value = content;" in body
+    assert "syncHighlighting();" in body
+    assert "_setMarkdownPreviewActive(true, { remember: false });" in body
+
+
+def test_doc_update_refreshes_preview_instead_of_hidden_editor_animation():
+    body = _function_body("handleDocUpdate")
+
+    visible = "const markdownPreviewWasVisible = _isMarkdownPreviewVisible();"
+    exit_preview = "if (markdownPreviewWasVisible) _setMarkdownPreviewActive(false, { remember: false });"
+    diff = "enterDiffMode(oldContent, newContent);"
+    refresh = "markdownPreviewWasVisible && _refreshMarkdownPreviewIfVisible(docId, newContent)"
+    animate = "_animateDocEdit(textarea, newContent);"
+
+    assert visible in body
+    assert exit_preview in body
+    assert diff in body
+    assert body.index(exit_preview) < body.index(diff)
+    assert refresh in body
+    assert body.index(refresh) < body.index(animate)
+    assert "_refreshMarkdownPreviewIfVisible(docId, newContent);" in body