PDF: expose object structure as a browsable filesystem

[andiwand]

🤖 Generated with Claude Code

What

Make a PDF's internal object structure browsable by exposing it through the filesystem API and wiring it to the existing filesystem HTML viewer.

New pdf::PdfFilesystem — a read-only ReadableFilesystem adapter over a PDF:

/trailer              the trailer dictionary
/objects/<id>_<gen>   each indirect object's value (stream dict for stream objects)
/streams/<id>_<gen>   each stream object's bytes (filter-decoded when possible, raw otherwise)

create_object_filesystem(pdf) wraps a PDF into an odr::Filesystem, so it browses and renders through the existing filesystem HTML viewer (html::translate(filesystem, …)) — no viewer changes needed.

How

• The object set is enumerated from the cross-reference table at construction (free entries and unreadable objects are skipped).
• Content is serialized lazily on open; the backing DocumentParser is held for the filesystem's lifetime, so an instance is transient — one per browse — matching the parser's usage contract.
• Stream decode failures (image codecs / unsupported filters) fall back to the raw stream bytes so the object stays inspectable.

Tests

test/src/internal/pdf/pdf_filesystem.cpp covers the object/stream listing, serialized object and trailer content, decoded stream bytes, and end-to-end rendering through the filesystem viewer.