docs: add MCP service design and implementation plan

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/plans/2026-03-08-mcp-service-design.md

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+# OpenNest MCP Service + IO Library Refactor
+
+## Goal
+
+Create an MCP server so Claude Code can load nest files, run nesting algorithms, and inspect results — enabling rapid iteration on nesting strategies without launching the WinForms app.
+
+## Project Changes
+
+```
+OpenNest.Core          (no external deps)  — add Plate.GetRemnants()
+OpenNest.Engine        → Core
+OpenNest.IO (NEW)      → Core + ACadSharp  — extracted from OpenNest/IO/
+OpenNest.Mcp (NEW)     → Core + Engine + IO
+OpenNest (WinForms)    → Core + Engine + IO (drops ACadSharp direct ref)
+```
+
+## OpenNest.IO Library
+
+New class library. Move from the UI project (`OpenNest/IO/`):
+
+- `DxfImporter`
+- `DxfExporter`
+- `NestReader`
+- `NestWriter`
+- `ProgramReader`
+- ACadSharp NuGet dependency (3.1.32)
+
+The WinForms project drops its direct ACadSharp reference and references OpenNest.IO instead.
+
+## Plate.GetRemnants()
+
+Add to `Plate` in Core. Simple strip-based scan:
+
+1. Collect all part bounding boxes inflated by `PartSpacing`.
+2. Scan the work area for clear rectangular strips along edges and between part columns/rows.
+3. Return `List<Box>` of usable empty regions.
+
+No engine dependency — uses only work area and part bounding boxes already available on Plate.
+
+## MCP Tools
+
+### Input
+| Tool | Description |
+|------|-------------|
+| `load_nest` | Load a `.nest` zip file, returns nest summary (plates, drawings, part counts) |
+| `import_dxf` | Import a DXF file as a drawing |
+| `create_drawing` | Create from built-in shape primitive (rect, circle, L, T) or raw G-code string |
+
+### Setup
+| Tool | Description |
+|------|-------------|
+| `create_plate` | Define a plate with dimensions, spacing, edge spacing, quadrant |
+| `clear_plate` | Remove all parts from a plate |
+
+### Nesting
+| Tool | Description |
+|------|-------------|
+| `fill_plate` | Fill entire plate with a single drawing (NestEngine.Fill) |
+| `fill_area` | Fill a specific box region on a plate |
+| `fill_remnants` | Auto-detect remnants via Plate.GetRemnants(), fill each with a drawing |
+| `pack_plate` | Multi-drawing bin packing (NestEngine.Pack) |
+
+### Inspection
+| Tool | Description |
+|------|-------------|
+| `get_plate_info` | Dimensions, part count, utilization %, remnant boxes |
+| `get_parts` | List placed parts with location, rotation, bounding box |
+| `check_overlaps` | Run overlap detection, return collision points |
+
+## Example Workflow
+
+```
+load_nest("N0308-008.zip")
+→ 1 plate (36x36), 75 parts, 1 drawing (Converto 3 YRD DUMPER), utilization 80.2%
+
+get_plate_info(plate: 0)
+→ utilization: 80.2%, remnants: [{x:33.5, y:0, w:2.5, h:36}]
+
+fill_remnants(plate: 0, drawing: "Converto 3 YRD DUMPER")
+→ added 3 parts, new utilization: 83.1%
+
+check_overlaps(plate: 0)
+→ no overlaps
+```
+
+## MCP Server Implementation
+
+- .NET 8 console app using stdio transport
+- Published to `~/.claude/mcp/OpenNest.Mcp/`
+- Registered in `~/.claude/settings.local.json`
+- In-memory state: holds the current `Nest` object across tool calls