Implement the q (push) and Q (pop) operators driving a Vec<GraphicsState>
save stack with the PDF spec's 64-level depth limit.
Changes:
- Changed MAX_GSTATE_DEPTH from 32 to 64 per PDF spec section 8.4
- Added gstate_overflow_logged flag to emit overflow diagnostic only once per page
- Q at depth 0 is a no-op that emits GSTATE_STACK_UNDERFLOW diagnostic
Acceptance criteria (all PASS):
- 64 nested q calls succeed; 65th emits diagnostic
- 64 q + 64 Q restores to initial state
- Q at depth 0 is a no-op (no panic)
- 1000 paired q...Q operations succeed (depth never exceeds 1)
- Diagnostic emitted exactly once per page even after multiple overflows
Closes: pdftract-1os1
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
