diff --git a/agent/context_compressor.py b/agent/context_compressor.py
index 2f1fecbac9..1bfd508f91 100644
--- a/agent/context_compressor.py
+++ b/agent/context_compressor.py
@@ -6045,8 +6045,8 @@ This compaction should PRIORITISE preserving all information related to the focu
         SimpleNamespace), for logging/display only. Matching logic must use
         :meth:`_tool_call_id_variants` instead — see its docstring."""
         if isinstance(tc, dict):
-            return tc.get("call_id", "") or tc.get("id", "") or ""
-        return getattr(tc, "call_id", "") or getattr(tc, "id", "") or ""
+            return (tc.get("call_id", "") or tc.get("id", "") or "").strip()
+        return (getattr(tc, "call_id", "") or getattr(tc, "id", "") or "").strip()
 
     @staticmethod
     def _tool_call_id_variants(tc) -> set:
@@ -6092,7 +6092,7 @@ This compaction should PRIORITISE preserving all information related to the focu
         result_call_ids: set = set()
         for msg in messages:
             if msg.get("role") == "tool":
-                cid = msg.get("tool_call_id")
+                cid = (msg.get("tool_call_id") or "").strip()
                 if cid:
                     # Expand alias spellings on the RESULT side too — a
                     # composite ``call|item`` tool_call_id must match a
diff --git a/tests/agent/test_context_compressor.py b/tests/agent/test_context_compressor.py
index ede4840a6c..c052c3fb1a 100644
--- a/tests/agent/test_context_compressor.py
+++ b/tests/agent/test_context_compressor.py
@@ -3619,3 +3619,60 @@ class TestPreLlmFeasibilityCheck:
             feasibility_skip=compressor._last_feasibility_skip,
         )
         assert compressor._fallback_compression_streak == 1
+
+
+class TestSanitizeToolPairsWhitespace:
+    """_sanitize_tool_pairs must strip whitespace from tool_call_id before
+    comparing, matching the fix applied to agent_runtime_helpers.py in
+    commit fa3ab2ffd.  Without stripping, a valid tool result whose
+    tool_call_id has surrounding whitespace is misclassified as orphaned
+    and silently replaced with a [Result unavailable] stub.
+    """
+
+    def _make(self):
+        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
+            return ContextCompressor(model="test/model", quiet_mode=True,
+                                     protect_first_n=2, protect_last_n=2)
+
+    def _assistant(self, call_id):
+        return {
+            "role": "assistant", "content": "",
+            "tool_calls": [{"id": call_id, "type": "function",
+                             "function": {"name": "f", "arguments": "{}"}}],
+        }
+
+    def test_leading_whitespace_on_result_id_preserved(self):
+        c = self._make()
+        msgs = [
+            self._assistant("call_abc"),
+            {"role": "tool", "tool_call_id": " call_abc", "content": "ok"},
+        ]
+        out = c._sanitize_tool_pairs(msgs)
+        tool_msgs = [m for m in out if m.get("role") == "tool"]
+        assert len(tool_msgs) == 1
+        assert tool_msgs[0]["content"] == "ok", "valid result must not be treated as orphaned"
+
+    def test_trailing_whitespace_on_result_id_preserved(self):
+        c = self._make()
+        msgs = [
+            self._assistant("call_xyz"),
+            {"role": "tool", "tool_call_id": "call_xyz  ", "content": "data"},
+        ]
+        out = c._sanitize_tool_pairs(msgs)
+        tool_msgs = [m for m in out if m.get("role") == "tool"]
+        assert len(tool_msgs) == 1
+        assert tool_msgs[0]["content"] == "data"
+
+    def test_truly_orphaned_still_removed(self):
+        """Whitespace-trimmed ID that still has no match must be removed.
+        The assistant's call_real has no matching result, so a stub is
+        inserted in its place — the original orphaned entry must be gone."""
+        c = self._make()
+        msgs = [
+            self._assistant("call_real"),
+            {"role": "tool", "tool_call_id": " call_orphan ", "content": "stale"},
+        ]
+        out = c._sanitize_tool_pairs(msgs)
+        tool_call_ids = [m.get("tool_call_id") for m in out if m.get("role") == "tool"]
+        assert "call_orphan" not in tool_call_ids, "genuinely orphaned result must be removed"
+        assert " call_orphan " not in tool_call_ids, "original whitespace form must also be gone"