Fixes#10927
Adds unique per-wrapper IDs to external-content boundary markers to
prevent spoofing attacks where malicious content could inject fake
marker boundaries.
- Generate random 16-char hex ID per wrap operation
- Start/end markers share the same ID for pairing
- Sanitizer strips markers with or without IDs (handles legacy + spoofed)
- Added test for attacker-injected markers with fake IDs
Co-authored-by: Vincent Koc <vincentkoc@ieee.org>
