docs(pdftract-147a): author SDK contract specification
Add comprehensive SDK contract specification at docs/notes/sdk-contract.md.
This document serves as the constitutional specification for all pdftract
SDK implementations across all languages.
The contract defines:
- Method surface (9 methods mirroring CLI/MCP tools)
- Error mapping (CLI exit codes → native exceptions)
- Versioning compatibility rules (MAJOR lock, MINOR flexibility)
- Option-naming conventions (CLI flag → language-native case)
- Native type-mapping requirements (Document, Page, Span, Block, Match, Fingerprint, Classification)
- Async conventions per language
- Conformance enforcement (100% pass required)
- Change policy (ADR required for contract changes)
Verification note: notes/pdftract-147a.md
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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