fix: salvage batch — compaction guidance, memory authority, cache eviction after compression

- Fix /compact → /compress in context-overflow tips (closes #20020)
- Evict cached agent after session hygiene and /compress so system
  prompt refreshes with current SOUL.md, memory, and skills
- Restore memory authority across compaction: change 'informational
  background data' to 'authoritative reference data' in memory block
  and SUMMARY_PREFIX, with backward-compatible regex

Based on:
- PR #20027 by @LeonSGP43
- PR #18767 by @MacroAnarchy
- PR #17380 by @vominh1919

PR #17121 boundary marker fix already merged to main (2eef395e1).
PR #9262 user-message anchoring already on main via _ensure_last_user_message_in_tail().

scripts/release.py

@@ -177,6 +177,8 @@ AUTHOR_MAP = {
     "git@local.invalid": "hendrixfreire",
     "1060770+benjaminsehl@users.noreply.github.com": "benjaminsehl",
     "nerijusn76@gmail.com": "Nerijusas",
+    # Compaction salvage batch (May 2026)
+    "MacroAnarchy@users.noreply.github.com": "MacroAnarchy",
     "itonov@proton.me": "Ito-69",
     "glesstech@gmail.com": "georgeglessner",
     "maxim.smetanin@gmail.com": "maxims-oss",