- Add ResourceStack for nested resource scope management
- Add ExecutionContext for cycle/depth detection in form XObject recursion
- Add execute_with_do() function with full graphics state support (q/Q/cm/Do)
- Add ImageXObject type for recording encountered images
- Add comprehensive tests for ResourceStack, ExecutionContext, and Do operator
Per Phase 3.3 (plan.md:1579-1593):
- Form XObject lookup via ResourceStack
- /Matrix application to CTM
- Cycle detection (STRUCT_XOBJECT_CYCLE)
- Depth limiting (STRUCT_DEPTH_EXCEEDED, max 20)
- Image XObject recording without glyph production
Acceptance criteria:
- ResourceStack shadowing: form resources shadow parent resources
- Cycle detection: duplicate XObject ID triggers STRUCT_XOBJECT_CYCLE
- Depth limit: 20-level max, triggers STRUCT_DEPTH_EXCEEDED
- Image XObjects: recorded with CTM-transformed bbox, no glyphs
Closes: pdftract-62uon
cbbe7e5f44