diff --git a/nanobot/agent/context_governance.py b/nanobot/agent/context_governance.py
index ed98cb2c..b2e1249f 100644
--- a/nanobot/agent/context_governance.py
+++ b/nanobot/agent/context_governance.py
@@ -425,9 +425,14 @@ class ContextGovernor:
         return system_messages + self._legal_history_tail(kept, non_system)
 
     @staticmethod
-    def _summary_for(message: dict[str, Any]) -> str:
+    def _tool_result_compaction_message(message: dict[str, Any]) -> str:
         name = message.get("name", "tool")
-        return f"[Prior {name} result compacted to fit context; the tool call already completed.]"
+        return (
+            f"Error: The previous {name} result was compacted to fit context because it was too "
+            "large. Do not repeat the same call unchanged. Retry with a narrower path, query, "
+            "range, or result limit, use another tool, or tell the user the task cannot fit in "
+            "the available context."
+        )
 
     def _legal_history_tail(
         self,
@@ -462,12 +467,12 @@ class ContextGovernor:
             tool_call_id = msg.get("tool_call_id")
             if not tool_call_id or str(tool_call_id) not in compacted_tool_call_ids:
                 continue
-            summary = self._summary_for(msg)
-            if msg.get("content") == summary:
+            compaction_message = self._tool_result_compaction_message(msg)
+            if msg.get("content") == compaction_message:
                 continue
             if updated is messages:
                 updated = [dict(m) for m in messages]
-            updated[idx]["content"] = summary
+            updated[idx]["content"] = compaction_message
         return updated
 
     def _inflight_compaction_candidates(
@@ -500,4 +505,4 @@ class ContextGovernor:
         return primary + fallback
 
     def _compact_tool_result_at(self, messages: list[dict[str, Any]], idx: int) -> None:
-        messages[idx]["content"] = self._summary_for(messages[idx])
+        messages[idx]["content"] = self._tool_result_compaction_message(messages[idx])
diff --git a/tests/agent/test_runner_governance.py b/tests/agent/test_runner_governance.py
index 7b22740f..7acbb684 100644
--- a/tests/agent/test_runner_governance.py
+++ b/tests/agent/test_runner_governance.py
@@ -574,7 +574,7 @@ def test_microcompact_overflow_compacts_to_low_watermark(monkeypatch):
 
 
 def test_microcompact_compacts_newest_when_it_alone_overflows(monkeypatch):
-    """The newest result is preserved only while the request can still fit."""
+    """An unfit newest result tells the model to retry narrowly or report the limit."""
     provider = MagicMock()
     provider.generation = SimpleNamespace(max_tokens=0)
     tools = MagicMock()
@@ -611,6 +611,9 @@ def test_microcompact_compacts_newest_when_it_alone_overflows(monkeypatch):
 
     tool_msg = next(m for m in result if m.get("role") == "tool")
     assert "compacted to fit context" in tool_msg["content"]
+    assert "Do not repeat the same call unchanged" in tool_msg["content"]
+    assert "Retry with a narrower path, query, range, or result limit" in tool_msg["content"]
+    assert "tell the user the task cannot fit" in tool_msg["content"]
     assert compacted_tool_call_ids == {"c0"}