fix: bump pygments to >=2.20 and fix Markdown rendering regression

- Bump pygments minimum version to 2.20 to avoid a bug in 2.19 where
  HtmlFormatter raises AttributeError when filename option is None
- Fix PyconDetectorPreprocessor fence regex to use a backreference so
  the closing fence matches the opening marker, preventing greedy
  over-consumption of adjacent fenced blocks
- Support both backtick and tilde fence styles in the detector
- Raise preprocessor priority (30 → 175) to run before pymdownx
- Guard against None return from markdown.markdown()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tschm

Makefile

@@ -138,7 +138,8 @@ py-snapshots:
 	uv run --group test pytest \
 		tests/_server/templates/test_templates.py \
 		tests/_server/api/endpoints/test_export.py \
-		tests/test_api.py
+		tests/test_api.py \
+		tests/test_project_dependencies.py
 
 ##############
 # Packaging  #

marimo/_output/md.py

@@ -35,7 +35,7 @@ class PyconDetectorExtension(markdown.Extension):
     def extendMarkdown(self, md: markdown.Markdown) -> None:
         """Add the preprocessor to the markdown instance."""
         processor = PyconDetectorPreprocessor(md)
-        md.preprocessors.register(processor, "pycon_detector", 30)
+        md.preprocessors.register(processor, "pycon_detector", 175)
 
 
 class PyconDetectorPreprocessor(markdown.preprocessors.Preprocessor):
@@ -53,9 +53,12 @@ class PyconDetectorPreprocessor(markdown.preprocessors.Preprocessor):
 
     def __init__(self, md: markdown.Markdown) -> None:
         super().__init__(md)
-        # Pattern to match fenced code blocks
+        # Pattern to match fenced code blocks (backreference \2 ensures the
+        # closing fence matches the opening fence marker, preventing greedy
+        # over-consumption of adjacent fenced blocks)
         self.fence_pattern = re.compile(
-            r"^(\s*)```(\w*)\s*\n(.*?)^(\s*)```\s*$", re.MULTILINE | re.DOTALL
+            r"^(\s*)(```+|~~~+)(\w*)\s*\n(.*?)^\s*\2\s*$",
+            re.MULTILINE | re.DOTALL,
         )
 
     def run(self, lines: list[str]) -> list[str]:
@@ -64,14 +67,14 @@ def run(self, lines: list[str]) -> list[str]:
 
         def replace_fence(match: re.Match[str]) -> str:
             indent = match.group(1)
-            language = match.group(2) or ""
-            code = match.group(3)
+            fence = match.group(2)
+            language = match.group(3) or ""
+            code = match.group(4)
 
             # Only process if no language is specified
-            if not language:
-                if self._detect_pycon(code):
-                    # Replace with pycon language
-                    return f"{indent}```pycon\n{code}{indent}```"
+            if not language and self._detect_pycon(code):
+                # Replace with pycon language
+                return f"{indent}{fence}pycon\n{code}{indent}{fence}"
 
             # Return original
             return match.group(0)
@@ -250,7 +253,10 @@ def __init__(
             text,
             extensions=_get_extensions(),
             extension_configs=_get_extension_configs(),
-        ).strip()
+        )
+        if html_text is None:
+            html_text = ""
+        html_text = html_text.strip()
         # replace <p> tags with <span> as HTML doesn't allow nested <div>s in <p>s
         html_text = html_text.replace(
             "<p>", '<span class="paragraph">'

pyproject.toml

@@ -20,7 +20,7 @@ dependencies = [
     # Pinned to specific version for introduction of codeblock handling.
     "pymdown-extensions>=10.15,<11",
     # syntax highlighting of code in markdown
-    "pygments>=2.19,<3",
+    "pygments>=2.20,<3",
     # for reading, writing configs
     "tomlkit>=0.12.0",
     # for managing frontmatter headers in markdown

tests/snapshots/dependencies.txt

@@ -8,7 +8,7 @@ msgspec>=0.20.0
 narwhals>=2.0.0
 packaging
 psutil>=5.0
-pygments>=2.19,<3
+pygments>=2.20,<3
 pymdown-extensions>=10.15,<11
 pyyaml>=6.0.1
 pyzmq>=27.1.0; python_version < '3.15'