CRITICAL REGRESSION: Plot markers missing in output (was working 2 weeks ago)

[krystophny]

REGRESSION ANALYSIS REQUIRED

Problem: Plot markers are not appearing in generated plots, functionality was working 2 weeks ago.

Regression Evidence: User confirms marker plotting was functional 2 weeks ago and has broken recently.

Required Actions:

1. Git history investigation: check commits from ~2 weeks ago (around 2025-08-17)
2. Git bisect to identify commit that broke marker rendering
3. Compare current marker output with historical working state
4. Restore marker plotting functionality

Technical Investigation:

• Check marker rendering implementation changes
• Verify marker drawing commands in backend
• Test marker functionality with known working commit
• Validate marker visibility across different backends

Priority: TOP - Sprint #1 emergency issue
Type: Regression defect requiring git history analysis