Why: docx preview already sniffs ZIP magic so a text file renamed to
.docx stays readable. xlsx and pptx loaders still fed those bytes to
the parser and surfaced a raw library error.
Evidence: npx tsc --noEmit and npx vitest run (40 tests) on this branch
after merging origin/main. Legacy .xls/.ppt skip the sniff because they
are not OOXML.
Impact: pseudo xlsx/pptx render as text with a short note. Real ZIP
workbooks and decks still use the existing parsers.
Refs: Dev PR #96, task feature/preview-sniff-fallback
Co-authored-by: Cursor <cursoragent@cursor.com>
Why: agent-generated ".docx" artifacts were historically plain text bytes
written via string-only write tools; the docx preview loader fed them
straight to mammoth/JSZip, which threw "Can't find end of central directory"
on the meeting-notes docx from the review session.
Evidence: docxLoader now checks the PK\x03\x04 (or empty-archive PK\x05\x06)
magic before mammoth; non-ZIP bytes render as markdown with a readable note
instead of an error. vitest 33/33 pass, tsc --noEmit clean.
Impact: stock fake-docx artifacts become readable immediately; real docx
previews unchanged. Rendering only, no API/contract change.
Refs: .task/feature-preview-sniff-fallback.md
weichenandCursor