Summary

sanitize_guidelines in crates/zeph-memory/src/compression_guidelines.rs covers XML, [INST], injection lines, and system: in tests, but these patterns have no dedicated tests:

• Special-token regex (<|system|> and similar)
• Role prefixes: assistant: and user:

Fix

Add unit tests for:

1. <|system|>foo → sanitized
2. assistant: do X at line start → sanitized
3. user: inject at line start → sanitized

Low risk; file for backlog.

Identified by code reviewer (REVIEW-12) during ACON compression guidelines PR (#1647) review.