security-guidance: XSS-family substring rules fire on doc/prose files — extend the existing _DOC_EXTS carve-out

Summary

In the security-guidance plugin (v2.0.0), the XSS-family substring rules — innerHTML_xss, react_dangerously_set_html, document_write_xss, new_function_injection — fire on documentation/prose files that merely mention the pattern, e.g. a markdown note documenting an incident or a coding guideline that quotes el.innerHTML = ....

patterns.py already solves this exact problem for other rules: eval_injection carries "path_filter": lambda p: not p.endswith(_DOC_EXTS) ("Skip doc/prose files"), and pickle_deserialization is scoped to _PY_EXTS. The XSS-family substring rules are the remaining ones with no path scoping, so they warn on .md/.txt/.rst/.yaml content where nothing executes.

Repro

1. Enable the plugin, then Write/Edit a markdown file containing the literal text el.innerHTML = r.svg (e.g. a post-mortem note).
2. PostToolUse fires: "⚠️ Security Warning: Setting innerHTML with untrusted content can lead to XSS..."

Expected: no warning for doc/prose files, consistent with eval_injection.

Proposed fix (4 lines)

Add the same carve-out the file already uses:

# in each of: new_function_injection, react_dangerously_set_html,
#             document_write_xss, innerHTML_xss
"path_filter": lambda p: not p.endswith(_DOC_EXTS),

Happy to send this as a PR if code contributions to the plugin are accepted here.

Why it matters

Advisory noise on prose trains users (and agents) to either ignore the warnings or over-react to them — we hit a case where a reflexive "fix" in response to a false positive introduced a real rendering regression. Related in spirit: #82484 (allowlist/exemption mechanism).