Summary

Fixes a Matrix rendering regression introduced by #18505: the new Matrix HTML sanitizer stripped table structure emitted by the existing Markdown tables extension.

Changes

• Add Matrix-compatible table structure tags to _MatrixHtmlSanitizer:
  • table
  • thead
  • tbody
  • tfoot
  • tr
  • th
  • td
• Preserve the existing sanitizer posture by continuing to strip unsafe attributes such as event handlers and inline styles.
• Add regression coverage for sanitized table HTML and optional Markdown-table output when the markdown package is installed.

Validation

.venv/bin/python -m pytest tests/gateway/test_matrix.py::TestMatrixMarkdownToHtml -q
.venv/bin/python -m pytest tests/gateway/test_matrix.py -q
.venv/bin/python -m py_compile gateway/platforms/matrix.py
git diff --check

Results:

• 13 passed, 1 skipped
• 230 passed, 1 skipped
• py_compile passed
• git diff --check passed