diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6a080547d9..d98746c7a4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Prevent compression-summary cards from using ordinary tool output that merely mentions context compression. The streaming path now reuses the shared strict compression-marker predicate, so only synthetic marker prefixes from non-tool messages can seed `compression_anchor_summary`; skill/tool JSON and user discussion about compaction no longer render as misleading `Context compaction` reference cards.
+
 ## [v0.51.118] — 2026-05-22 — Release CP (stage-pr2773 — 1-PR hotfix — v0.51.117 brick fix: chat input restored)
 
 ### Fixed
diff --git a/api/compression_anchor.py b/api/compression_anchor.py
index f251851c4f..12d964158b 100644
--- a/api/compression_anchor.py
+++ b/api/compression_anchor.py
@@ -53,7 +53,7 @@ def _content_has_part_type(content, part_types):
     )
 
 
-def _is_context_compression_marker(message):
+def is_context_compression_marker(message):
     """Return true for synthetic compression/reference cards, not user turns."""
     if not isinstance(message, dict):
         return False
@@ -71,6 +71,11 @@ def _is_context_compression_marker(message):
     )
 
 
+def _is_context_compression_marker(message):
+    """Backward-compatible alias for callers that have not switched yet."""
+    return is_context_compression_marker(message)
+
+
 def visible_messages_for_anchor(messages, *, auto_compression: bool = False):
     """Return transcript messages that can anchor compression UI metadata.
 
diff --git a/api/streaming.py b/api/streaming.py
index 663d84d174..5718ee1c8f 100644
--- a/api/streaming.py
+++ b/api/streaming.py
@@ -35,7 +35,7 @@
     load_settings,
 )
 from api.helpers import redact_session_data, _redact_text
-from api.compression_anchor import visible_messages_for_anchor
+from api.compression_anchor import is_context_compression_marker, visible_messages_for_anchor
 from api.metering import meter
 from api.run_journal import RunJournalWriter
 from api.turn_journal import append_turn_journal_event_for_stream
@@ -2299,15 +2299,7 @@ def _dedupe_replayed_active_context(previous_context, result_messages):
 
 
 def _is_context_compression_marker(msg):
-    if not isinstance(msg, dict):
-        return False
-    text = _message_text(msg.get('content', '')).lower()
-    return (
-        'context compaction' in text
-        or 'context compression' in text
-        or 'context was auto-compressed' in text
-        or 'active task list was preserved across context compression' in text
-    )
+    return is_context_compression_marker(msg)
 
 
 def _compact_summary_text(raw_text: str | None, limit: int = 320) -> str | None:
diff --git a/tests/test_issue2028_compression_anchor_helpers.py b/tests/test_issue2028_compression_anchor_helpers.py
index 1fcb4f6ad8..d675d2a004 100644
--- a/tests/test_issue2028_compression_anchor_helpers.py
+++ b/tests/test_issue2028_compression_anchor_helpers.py
@@ -4,7 +4,8 @@
 
 from pathlib import Path
 
-from api.compression_anchor import visible_messages_for_anchor
+from api.compression_anchor import is_context_compression_marker, visible_messages_for_anchor
+from api.streaming import _compression_summary_from_messages, _is_context_compression_marker
 
 
 def test_legacy_duplicate_anchor_helpers_are_removed():
@@ -57,3 +58,42 @@ def test_visible_messages_for_anchor_keeps_manual_user_messages_simple():
         [user_tool_metadata, user_attachment, assistant_tool_metadata],
         auto_compression=True,
     ) == [user_tool_metadata, user_attachment, assistant_tool_metadata]
+
+
+def test_context_compression_marker_detection_is_prefix_and_role_scoped():
+    real_marker = {
+        "role": "assistant",
+        "content": "[CONTEXT COMPACTION — REFERENCE ONLY] Earlier turns were compacted.",
+    }
+    preserved_tasks_marker = {
+        "role": "user",
+        "content": "[Your active task list was preserved across context compression] - [ ] follow up",
+    }
+    tool_noise = {
+        "role": "tool",
+        "content": "{\"description\": \"Troubleshoot frequent context compression indicators\"}",
+    }
+    user_discussion = {
+        "role": "user",
+        "content": "Why do I see context compression after every message?",
+    }
+
+    assert is_context_compression_marker(real_marker)
+    assert is_context_compression_marker(preserved_tasks_marker)
+    assert _is_context_compression_marker(real_marker)
+    assert not is_context_compression_marker(tool_noise)
+    assert not is_context_compression_marker(user_discussion)
+
+
+def test_compression_summary_ignores_tool_output_that_mentions_compression():
+    marker = {
+        "role": "assistant",
+        "content": "[CONTEXT COMPACTION — REFERENCE ONLY] Keep this handoff as reference.",
+    }
+    skill_tool_output = {
+        "role": "tool",
+        "content": "{\"name\": \"hermes-webui-operations\", \"content\": \"Troubleshooting frequent context compression indicators...\"}",
+    }
+
+    assert _compression_summary_from_messages([marker, skill_tool_output]) == marker["content"]
+    assert _compression_summary_from_messages([skill_tool_output]) is None