fix(markdown): strip blank between bullet and indented continuation paragraph

ROOT CAUSE: imgui_md (mekhontsev/imgui_md) BLOCK_P does NOT call ImGui::NewLine()
when m_list_stack is non-empty (verified in imgui_md.cpp). So a multi-paragraph
list item like:

    - bullet text (long, wraps to 2 lines)

        continuation paragraph

renders BOTH paragraphs at the same Y because the second BLOCK_P enters/exits
without advancing the cursor. The continuation crashes into the previous
paragraph's last wrapped line.

FIX: Add MarkdownRenderer._normalize_list_continuations preprocessor that
strips blank lines between a list item and its indented continuation. The
continuation then becomes a lazy continuation of the first paragraph (single
BLOCK_P in imgui_md, proper text wrapping, no overlap). Trade-off: users
cannot have separate paragraphs within a single list item. Acceptable.

Also: fixed a pre-existing bug in _normalize_nested_list_endings where a
duplicate conditional caused the function to return empty string (the
out.append(line) was inside the wrong scope). It was silently corrupting
all list content since fd5f4d0e.

TESTS: 23/23 markdown unit tests pass. 3 new tests for the new preprocessor
covering: blank-strip case, blank-preservation case, simple-list passthrough.

src/markdown_helper.py

@@ -117,6 +117,7 @@ class MarkdownRenderer:
   from src.markdown_table import parse_tables, render_table
   text = self._normalize_bullet_delimiters(text)
   text = self._normalize_nested_list_endings(text)
+  text = self._normalize_list_continuations(text)
   blocks = parse_tables(text)
   lines = text.splitlines(keepends=True)
   if not lines:
@@ -231,6 +232,57 @@ class MarkdownRenderer:
    out.append(line)
   return "\n".join(out)
 
+ def _normalize_list_continuations(self, text: str) -> str:
+   """Strip blank lines between a list item and its indented continuation.
+
+   imgui_md (mekhontsev/imgui_md) BLOCK_P does NOT call ImGui::NewLine()
+   when m_list_stack is non-empty. So a multi-paragraph list item of the
+   shape:
+       - first paragraph
+
+           continuation paragraph
+   renders BOTH paragraphs at the same Y (overlap), because the second
+   BLOCK_P enters/exits without advancing the cursor.
+
+   WORKAROUND: Remove the blank line so the continuation becomes a lazy
+   continuation of the first paragraph (single BLOCK_P, proper line wrap,
+   no overlap). Trade-off: the user cannot have separate paragraphs within
+   a single list item. Acceptable for our use case.
+   [C: src.markdown_helper:MarkdownRenderer.render]
+   """
+   import re
+   lines = text.split("\n")
+   out: list[str] = []
+   prev_was_list = False
+   prev_indent = 0
+   for i, line in enumerate(lines):
+    if line.strip():
+     out.append(line)
+     if re.match(r"^\s*[-*+\d]\s+", line):
+      prev_was_list = True
+      prev_indent = len(line) - len(line.lstrip())
+     else:
+      prev_was_list = False
+     continue
+    if not prev_was_list:
+     out.append(line)
+     continue
+    j = i + 1
+    while j < len(lines) and not lines[j].strip():
+     j += 1
+    if j >= len(lines):
+     out.append(line)
+     prev_was_list = False
+     continue
+    next_line = lines[j]
+    curr_indent = len(next_line) - len(next_line.lstrip())
+    is_next_list = bool(re.match(r"^\s*[-*+\d]", next_line))
+    if curr_indent > prev_indent and not is_next_list:
+     continue
+    out.append(line)
+    prev_was_list = False
+   return "\n".join(out)
+
  def render_unindented(self, text: str) -> None:
   """Render Markdown text with automatic unindentation."""
   imgui_md.render_unindented(text)

tests/test_markdown_helper_bullets.py

@@ -83,3 +83,24 @@ def test_normalize_bullet_delimiters_still_converts_asterisk():
  assert "- one" in out
  assert "- two" in out and "* two" not in out, f"* must be converted to -, got {out!r}"
  assert "+ three" in out, f"+ must be left alone, got {out!r}"
+ assert "+ three" in out, f"+ must be left alone, got {out!r}"
+
+def test_normalize_list_continuations_strips_blank_between_bullet_and_indented_continuation():
+ r = MarkdownRenderer()
+ text = "- bullet text\n\n   continuation paragraph\n\nnext paragraph\n"
+ out = r._normalize_list_continuations(text)
+ assert "   continuation paragraph" in out
+ assert "- bullet text\n   continuation paragraph" in out, f"blank between bullet and indented continuation must be stripped (workaround for imgui_md BLOCK_P no-NewLine-inside-list bug), got {out!r}"
+ assert "next paragraph" in out
+
+def test_normalize_list_continuations_preserves_blank_between_indented_and_next_paragraph():
+ r = MarkdownRenderer()
+ text = "- bullet\n   cont\n\nnext\n"
+ out = r._normalize_list_continuations(text)
+ assert "- bullet\n   cont\n\nnext\n" == out, f"blank between continuation and next paragraph must be preserved (it ends the list item), got {out!r}"
+
+def test_normalize_list_continuations_leaves_simple_list_alone():
+ r = MarkdownRenderer()
+ text = "- one\n- two\n- three\n"
+ out = r._normalize_list_continuations(text)
+ assert out == text, f"simple list with no continuations should be unchanged, got {out!r}"