fix(docs): mkdocs build with Pygments 2.20 and pymdown-extensions

Register a small MkDocs hook that coerces BlockHtmlFormatter filename=None
to an empty string before Pygments html.escape, fixing strict builds when
mkdocstrings highlights signatures without a title.

Made-with: Cursor

Author: mplatzer

mkdocs.yml

@@ -32,6 +32,9 @@ nav:
   - Getting started: index.md
   - API Reference: api.md
 
+hooks:
+  - mkdocs_pygments_hook.py
+
 plugins:
   - search
   - mkdocstrings:

mkdocs_pygments_hook.py

@@ -0,0 +1,36 @@
+# Copyright 2025 MOSTLY AI
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""MkDocs hook: Pygments 2.20+ HtmlFormatter expects filename to be a string.
+
+pymdown-extensions can pass filename=None when highlighting block code with no
+title (e.g. mkdocstrings signatures), which breaks html.escape().
+"""
+
+
+def on_config(config, **kwargs):
+    import pymdownx.highlight as ph
+
+    if not getattr(ph, "pygments", False):
+        return config
+
+    _orig = ph.BlockHtmlFormatter.__init__
+
+    def __init__(self, **options):
+        if options.get("filename") is None:
+            options = {**options, "filename": ""}
+        _orig(self, **options)
+
+    ph.BlockHtmlFormatter.__init__ = __init__  # type: ignore[method-assign]
+    return config