Preserve printed page numbers from PP-DocLayoutV3 number regions in SDK output

[VooDisss]

Summary

GLM-OCR currently detects PP-DocLayoutV3 layout regions, but printed page number regions labeled as number are not reliably preserved as OCR-derived metadata in saved SDK JSON output. The SDK should route number regions through OCR, keep the general json_result schema lean, and expose explicit printed-page metadata only when real printed-page data exists.

Proposed solution

Implement printed page number support in the SDK with the following behavior:

• Route PP-DocLayoutV3 number regions through OCR instead of dropping them
• Keep extraction strict: only use native_label == "number"
• Extract printed page number evidence in the result formatter
• Support both numeric and Roman numeral page labels
• Add three top-level JSON layers when printed-page data exists:
  • page_number_candidates
  • document_page_numbering
  • page_metadata
• Keep final general json_result blocks lean
  • do not expose broad transient layout metadata like layout_index / layout_score on all blocks
  • retain native_label in blocks
• Wrap saved paper.json only when real printed-page data exists
  • feature off -> legacy flat JSON
  • feature on, no hits -> legacy flat JSON
  • feature on, hits -> wrapped JSON with the printed-page layers
• Expose feature enablement via constructor, environment variable, and YAML config
• Keep MaaS and self-hosted output contracts aligned

Why this is needed

Printed page numbers are a distinct layout signal that should be preserved separately from file page position. They are useful technical metadata for downstream consumers that need explicit page labeling grounded in OCR-recognized page folios rather than only file-page ordering.

Scope constraints

This proposal is intentionally narrow:

• no header/footer/text fallback in this change
• no extrapolation of missing page labels in this change
• no debug-only artifacts in final SDK output

A later follow-up can add inferred full-document page mapping if needed, but this issue is only about preserving and exposing observed printed page number data cleanly in the SDK output contract.