Phase 7.4.5 implementation: Wire combined Vec<(String, FormFieldValue)> from
combiner into document-level /form_fields JSON output with tagged union schema.
- Add FormFieldJson, FormFieldTypeJson, FormFieldValueJson, ChoiceValueJson to schema
- Add form_fields: Vec<FormFieldJson> to ExtractionResult (always emitted, empty when none)
- Implement acro_field_to_value() converter for Phase 7.4.2 type-specific extraction
- Wire form field extraction in extract_pdf(): walk AcroForm, extract XFA, combine with XFA-wins
- Add convert_form_field_to_json() helper for FormFieldValue → FormFieldJson conversion
- Update docs/schema/v1.0/pdftract.schema.json with form_fields $defs and required field
- Add form_fields_to_markdown() to markdown module for Form Fields footer table
Schema shape: /form_fields is array of {name, type, value, default?, page_index?, rect?,
required, read_only, multiline?, max_length?, options?, multi_select?, selected?,
state_name?, pushbutton?, radio?}. Type field is tagged enum: "text", "button", "choice",
"signature". Value field varies by type (string|boolean|string|array|uint|null).
Closes: pdftract-5qca
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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