plan.md (#4)

* plan.md

* feat: grid tests

* feat: import SVG and STL format

* feat: changelog

* feat: roundedBox and text

* feat: circularArray

* fix: circArray sample

* feat: mirror

* chore: deps

Author: BCsabaEngine

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+## [2025-11-23]
+
+### Features
+
+#### Mirror Operations
+
+- **MIRROR Method**: Create reflections and symmetric objects across axis planes
+  - New `Solid.MIRROR(solid, axis)` static method for mirroring geometry
+  - Axis options: 'X' (YZ plane), 'Y' (XZ plane), 'Z' (XY plane)
+  - Returns mirrored copy (combine with UNION for bilateral symmetry)
+  - Immutable operation - does not modify original solid
+  - Works with all primitives, CSG results, and negative solids
+  - Supports chaining for multi-axis symmetry (quadrant, octant)
+  - Common use cases: symmetric gears, arches, propellers, organic forms
+
+#### Import Capabilities
+
+- **STL File Import**: Load external STL files (binary and ASCII formats) as Solid components
+  - New `Solid.fromSTL()` method for importing 3D models
+  - Automatic normalization for seamless CSG operations
+  - Full support for transforms, boolean operations, and grid arrays
+  - Uses Three.js STLLoader (no additional dependencies)
+
+- **SVG Path Import**: Import SVG paths and extrude them into 3D profiles
+  - New `Solid.profilePrismFromSVG()` method for extruding SVG paths
+  - Supports all standard SVG path commands (M/m, L/l, H/h, V/v, C/c, Q/q, A/a, Z/z)
+  - Automatic Y-axis coordinate conversion (SVG Y-down → 3D Y-up)
+  - Perfect for logos, custom profiles, and 2D designs
+  - Uses Three.js SVGLoader (no additional dependencies)
+
+- **Combined Import Operations**: Imported geometries work seamlessly with CSG operations
+  - STL + primitives boolean operations
+  - SVG + STL combinations
+  - Grid arrays from imported geometries
+
+#### New Examples
+
+- Added comprehensive tutorial `P.mirror.ts` with 7 example components
+  - Simple mirroring and bilateral symmetry
+  - Quadrant and octant (full 3D) symmetry
+  - Symmetric gears with mirrored tooth patterns
+  - Mirrored holes and mounting patterns
+  - Architectural archway with symmetric pillars
+
+- Added comprehensive tutorial `N-importing.ts` with 14 example components
+  - STL import basics, transformations, and boolean operations
+  - SVG shapes: rectangles, stars, curves, hearts
+  - Advanced combinations: parametric imports, STL+SVG mixing, grid patterns
+- Added sample STL asset (`projects/examples/assets/sample.stl`) for testing
+
+### Improvements
+
+#### Code Architecture
+
+- Extracted path segment types to dedicated module (`src/lib/3d/path-factories.ts`)
+  - `StraightSegment` and `CurveSegment` types now in separate file
+  - `straight()` and `curve()` factory functions modularized
+  - Better code organization and reusability
+
+#### Input Validation
+
+- Enhanced validation across all primitive creation methods
+  - Comprehensive validation for cube, cylinder, sphere, cone, and prism
+  - Transform method validation (scale, rotate, move, at)
+  - Better error handling for edge cases
+  - NaN and Infinity detection with clear error messages
+  - Zero and negative dimension validation
+
+### Testing
+
+- Added comprehensive validation test suite (`tests/unit/lib/3d/Solid.validation.test.ts`)
+  - 380 lines of test coverage
+  - Primitive validation tests for all geometry types
+  - Transform validation tests (scale, rotate, move, at)
+  - Edge case coverage: very small values, very large values, NaN, Infinity
+  - Zero dimensions and negative value handling tests
+
+### Documentation
+
+- Updated `CLAUDE.md` with complete import capabilities documentation
+  - STL import usage and examples
+  - SVG path import usage and supported commands
+  - Boolean operations with imported geometries
+- Updated `README.md` with import feature overview
+- Added extensive inline comments in example files
+
+### Internal
+
+- Added project planning document (`plan.MD`)
+- Merged fixes from main branch (wedge positions)