feat(rex/comments): render combined.md → HTML for Zotero notes

Pure function over (str)→str. Reuses combine.parse_combined to peel
off the YAML frontmatter, runs the body through markdown-it-py with
table support enabled (CMS comments lean on tabular data).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/rex/comments/render.py

@@ -0,0 +1,26 @@
+"""Render combined.md → HTML for Zotero notes.
+
+combined.md is the per-comment aggregate written by ``combine.extract_comment``:
+a YAML frontmatter block followed by an inline-body section and one H2 section
+per attachment. Zotero notes accept HTML, so we strip the frontmatter and run
+the body through markdown-it-py.
+"""
+
+from __future__ import annotations
+
+from markdown_it import MarkdownIt
+
+from rex.comments.combine import parse_combined
+
+_MD = MarkdownIt("commonmark", {"html": False, "breaks": False, "linkify": True})
+_MD.enable("table")
+
+
+def render_combined_md(text: str) -> str:
+    """Strip combined.md's YAML frontmatter, render body to HTML.
+
+    Raises ValueError if the input is missing frontmatter — combined.md
+    always has it, so a missing block means the input isn't combined.md.
+    """
+    _, body = parse_combined(text)
+    return _MD.render(body)

tests/rex/comments/test_render.py

@@ -0,0 +1,51 @@
+"""rex.comments.render — combined.md → Zotero-edible HTML."""
+
+from __future__ import annotations
+
+from rex.comments.render import render_combined_md
+
+
+def test_strips_frontmatter():
+    md = "---\ncomment_id: CMS-2024-0001-0001\nstatus: ok\n---\n\n# Heading\n\nbody\n"
+    html = render_combined_md(md)
+    assert "comment_id" not in html
+    assert "status: ok" not in html
+    assert "<h1>Heading</h1>" in html
+    assert "<p>body</p>" in html
+
+
+def test_renders_basic_markdown():
+    md = "---\nstatus: ok\n---\n\n## Section\n\nText with **bold** and *italic*.\n"
+    html = render_combined_md(md)
+    assert "<h2>Section</h2>" in html
+    assert "<strong>bold</strong>" in html
+    assert "<em>italic</em>" in html
+
+
+def test_renders_tables():
+    md = (
+        "---\nstatus: ok\n---\n\n"
+        "| Col A | Col B |\n"
+        "| --- | --- |\n"
+        "| a1 | b1 |\n"
+        "| a2 | b2 |\n"
+    )
+    html = render_combined_md(md)
+    assert "<table>" in html
+    assert "<th>Col A</th>" in html
+    assert "<td>a1</td>" in html
+
+
+def test_handles_empty_body():
+    md = "---\nstatus: ok\n---\n\n"
+    html = render_combined_md(md)
+    assert html == "" or html.strip() == ""
+
+
+def test_raises_on_missing_frontmatter():
+    """combined.md is always written with frontmatter — guard against
+    silently ingesting malformed input."""
+    import pytest
+
+    with pytest.raises(ValueError, match="frontmatter"):
+        render_combined_md("# No frontmatter here\n")