feat: MCP refactor Phases 1-7 — enterprise engineering drawing extraction stack

[shrikantaprasad]

Summary

7-phase incremental refactor converting DocStrange into a production-ready engineering drawing extraction stack with MCP, FastAPI, and a full test suite.

Phase	What changed
1	Modular extractors (title_block, dimensions, notes, gdt, bom, revisions) + OCRServiceFactory fallback chain
2	Pydantic v2 schemas — typed ExtractionMetadata, page on all elements, BOMRow/RevisionEntry text auto-fill
3	OverlayGenerator with per-page filtering + critical OCR corruption bug fix (see below)
4	Async FastAPI service — validated uploads (415/400/413), typed response models, CORS
5	Modular MCP server split into tools.py / cache.py / server.py — LRU stat-based cache, page param on overlay tools
6	Overlay JSON — deterministic change_id (chg_001…), bbox field, summary.by_type counts
7	47-test extraction accuracy suite covering edge cases, bbox precision, multi-page stamping, schema validation

New module map

docstrange/
├── extractors/          # 6 modular extractors + base
├── schemas/engineering.py
├── pipelines/engineering.py
├── overlays/generator.py
├── api/                 # FastAPI — routes.py, models.py, main.py
└── mcp_server/          # tools.py, cache.py, server.py
tests/
├── test_extractors.py, test_schemas.py, test_pipeline.py
├── test_e2e_engineering.py, test_api.py
├── test_mcp_server.py, test_overlays.py
└── test_extraction_accuracy.py

Critical bug fix — OCR text corruption (Phase 3)

layout_detector._post_process_text() was silently corrupting engineering data:

• | → I — destroyed all GD&T feature control frames (|⊥|0.05|A| → I⊥I0.05IA)
• 0 → o and 1 → l — destroyed dimension values (25.40 → 25.4o)

These substitutions have been removed entirely.

Breaking changes

Overlay annotation JSON shape changed in Phase 6:

Field	Before	After
annotation ID	"id": "uuid-..."	"change_id": "chg_001"
pixel bbox	"bbox_pixels": {...}	"bbox": {...}
top-level	—	"summary": {"by_type": {...}, "total": N} added

Any existing consumers of the overlay JSON will need to update field references.

Quick start

# FastAPI service
pip install -e ".[dev]"
uvicorn docstrange.api.main:app --reload
# → http://localhost:8000/docs

# MCP server (Claude Desktop)
python -m docstrange.mcp_server

Test plan

• 168 tests passing across all phases (< 3 seconds)
• python -m pytest tests/test_extraction_accuracy.py tests/test_overlays.py tests/test_mcp_server.py tests/test_api.py tests/test_pipeline.py tests/test_e2e_engineering.py tests/test_extractors.py tests/test_schemas.py -q

🤖 Generated with Claude Code