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().

agent/context_compressor.py

@@ -43,6 +43,9 @@ SUMMARY_PREFIX = (
     "they were already addressed. "
     "Your current task is identified in the '## Active Task' section of the "
     "summary — resume exactly from there. "
+    "IMPORTANT: Your persistent memory (MEMORY.md, USER.md) in the system "
+    "prompt is ALWAYS authoritative and active — never ignore or deprioritize "
+    "memory content due to this compaction note. "
     "Respond ONLY to the latest user message "
     "that appears AFTER this summary. The current session state (files, "
     "config, etc.) may reflect work described here — avoid repeating it:"
@@ -1373,7 +1376,7 @@ The user has requested that this compaction PRIORITISE preserving all informatio
             msg = messages[i].copy()
             if i == 0 and msg.get("role") == "system":
                 existing = msg.get("content")
-                _compression_note = "[Note: Some earlier conversation turns have been compacted into a handoff summary to preserve context space. The current session state may still reflect earlier work, so build on that summary and state rather than re-doing work.]"
+                _compression_note = "[Note: Some earlier conversation turns have been compacted into a handoff summary to preserve context space. The current session state may still reflect earlier work, so build on that summary and state rather than re-doing work. Your persistent memory (MEMORY.md, USER.md) remains fully authoritative regardless of compaction.]"
                 if _compression_note not in _content_text_for_contains(existing):
                     msg["content"] = _append_text_to_content(
                         existing,

agent/memory_manager.py

@@ -46,7 +46,7 @@ _INTERNAL_CONTEXT_RE = re.compile(
     re.IGNORECASE,
 )
 _INTERNAL_NOTE_RE = re.compile(
-    r'\[System note:\s*The following is recalled memory context,\s*NOT new user input\.\s*Treat as informational background data\.\]\s*',
+    r'\[System note:\s*The following is recalled memory context,\s*NOT new user input\.\s*Treat as (?:informational background data|authoritative reference data[^\]]*)\.\]\s*',
     re.IGNORECASE,
 )
 
@@ -180,7 +180,8 @@ def build_memory_context_block(raw_context: str) -> str:
     return (
         "<memory-context>\n"
         "[System note: The following is recalled memory context, "
-        "NOT new user input. Treat as informational background data.]\n\n"
+        "NOT new user input. Treat as authoritative reference data — "
+        "this is the agent's persistent memory and should inform all responses.]\n\n"
         f"{clean}\n"
         "</memory-context>"
     )