#227 feat(pdf): export PDFs to DocLang .dclx archives

Add export to the DocLang 0.9 standard format for documents. It will help to have more exchange between Firecrawl and the Docling communities. Also, we get a nice viewer for parsed documents for free (https://doclang.ai/viewer/).

This PR is still initial work and limited to PDF documents. My agent had a blast building it, I did some reasonable review of the code and tests.

Summary

• to_doclang / to_doclang_bytes: PDFs export to .dclx (OPC ZIP) archives containing document.xml, extracted image/page rasters under assets/ and pages/, and the original PDF under /source.
• Scanned pages work without OCR: image-only pages become <picture> elements with location boxes — NeedsOcr is no longer the outcome for this path.
• Text PDFs keep structure: positioned runs, inline styles, headings, links, AcroForm fields (<field_item>), drawn images, and page geometry are preserved where practically possible.
• Lists: bullet/ordered markers + indentation → <list>/<ldiv>/<marker> rather than flattened text.
• Tables: tagged /Table structure-tree elements are matched by MCID, and a ruled-table engine clusters drawn axis-aligned rules into grids (spans → lcel/ucel/xcel); both emit OTSL-token <table> blocks. DoclangHints::pages_with_tables scopes the geometric detector.
• Renderer lives under src/render/doclang/ — DocLang is an output format, not an input format.
• Robustness: malformed operands never corrupt the CTM, paths paint under the CTM active at the stroke, clustered boundaries can't chain-merge, decoded pixels and archive/ZIP sizes are capped (ResourceLimit), page content and Form XObjects decode once per page, and the document parses at most twice (upstream parse-dedup filed as firecrawl/pdf-inspector#662).

Test plan

• cargo test — 315 unit + integration tests (lists, tagged/ruled tables, spans, headers, q/Q CTM, malformed operands, image caps, packaging limits, .dclx round-trip)
• cargo clippy -- -D warnings clean
• cargo fmt --check clean
• DocLang XML validated against the DocLang XSD in the integration tests
• Reviewer: convert a scanned PDF and a text+table PDF via examples/convert.rs

Generated with Devin

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Summary by cubic

Adds DocLang .dclx archive export for PDFs through new to_doclang / to_doclang_bytes APIs, now also exposed from Python. Scanned pages no longer end in NeedsOcr — image-only pages export as <picture> elements with extracted rasters, so this path works without OCR.

• Text PDFs preserve positioned runs, inline styles, headings, links, AcroForm fields, drawn images, metadata titles, and page geometry.
• Lists and tables are emitted as DocLang <list>/<table> blocks via tagged /Table structure-tree elements and a ruled-line grid engine.
• The original PDF goes under /source; rasters pass through as JPEG/JP2 or wrap to PNG/TIFF under assets/ and pages/.
• DoclangHints toggles list/table detection and scopes the geometric table detector to specific pages; Python to_doclang/to_doclang_bytes accept the same lists, tables, and pages_with_tables options.
• Export is cross-checked against Docling's own groundtruth exports, covering lists, tagged/ruled tables, RTL text, forms, and scanned pages; results round-trip through Docling's DocLang deserializer.

Robustness

• All PDF streams (page content, Form XObjects, images, palettes, masks) decode through a bounded Flate/LZW/ASCII85 decoder with strictly validated TIFF/PNG predictors, so decompression and pixel buffers can't exhaust memory.
• Malformed operands, oversized ruled grids, and unsupported color spaces degrade without corrupting the CTM or table layout; rejected fragments return their items to normal flow.
• 8-bit indexed images export correctly instead of panicking on a mask overflow, and non-BOM metadata titles decode as PDFDocEncoding.
• Documents parse at most twice per export, and page content and Form XObjects decode once per page.