diff --git a/agent/context_compressor.py b/agent/context_compressor.py
index 45ede22c9b54..d249f9898b69 100644
--- a/agent/context_compressor.py
+++ b/agent/context_compressor.py
@@ -4193,16 +4193,39 @@ This compaction should PRIORITISE preserving all information related to the focu
                     summary_body and _NO_USER_TASK_SENTINEL in summary_body
                 )
             summary_indices = {idx for idx, _ in summary_hits}
+            # Summary rows are excluded from the summarizer input (their
+            # bodies already ride _previous_summary), BUT a merged handoff
+            # carries genuine prior-tail user content before the delimiter —
+            # unwrap it (via the strip helper) into the window instead of
+            # dropping it (#47274 interplay with the multi-fossil scan).
+            def _window_row(idx: int, msg: Dict[str, Any]):
+                if idx not in summary_indices:
+                    return msg
+                stripped = self._strip_context_summary_handoff_message(
+                    _fresh_compaction_message_copy(msg)
+                )
+                return stripped  # None for standalone handoffs → dropped
             pre_summary_turns = [
-                msg for idx, msg in enumerate(
+                row for idx, msg in enumerate(
                     messages[compress_start:summary_idx],
                     start=compress_start,
                 )
-                if idx not in summary_indices
+                if (row := _window_row(idx, msg)) is not None
             ]
             turns_to_summarize = (
                 pre_summary_turns + messages[summary_idx + 1:compress_end]
             )
+            # The newest hit itself may be a merged handoff too — recover its
+            # prior-tail content the same way.
+            _newest_stripped = self._strip_context_summary_handoff_message(
+                _fresh_compaction_message_copy(messages[summary_idx])
+            )
+            if _newest_stripped is not None:
+                turns_to_summarize = (
+                    pre_summary_turns
+                    + [_newest_stripped]
+                    + messages[summary_idx + 1:compress_end]
+                )
             if summary_idx >= compress_end:
                 tail_start = summary_idx + 1
         elif self._previous_summary:
diff --git a/tests/agent/test_context_compressor_summary_continuity.py b/tests/agent/test_context_compressor_summary_continuity.py
index e5be05d55c3e..18b4c76b6256 100644
--- a/tests/agent/test_context_compressor_summary_continuity.py
+++ b/tests/agent/test_context_compressor_summary_continuity.py
@@ -203,25 +203,42 @@ def test_legacy_string_merged_handoff_preserves_real_tail_text():
 
 
 def test_recompression_of_current_merged_handoff_preserves_prior_tail_once():
-    """Current merged handoffs lose only stale summary data on recompression."""
+    """Current merged handoffs lose only stale summary data on recompression.
+
+    Composed contract after #57835 (restart head-protection decay): the
+    merged handoff's genuine prior-tail content must be RECOVERED — either
+    verbatim in the output (pre-decay head protection) or by entering the
+    summarizer input so the fresh summary folds it in (post-decay). It must
+    never be silently deleted, and the stale summary body must never be
+    re-emitted verbatim.
+    """
     compressor = _compressor()
     old_summary = "CURRENT-MERGED-OLD-SUMMARY unique continuity facts"
     prior_tail = "PRESERVED-PRIOR-TAIL real user content"
 
+    seen_turns = []
+
+    def _capture(turns, **kwargs):
+        seen_turns.extend(turns)
+        return ContextCompressor._with_summary_prefix(
+            "fresh replacement summary"
+        )
+
     with patch.object(
         compressor,
         "_generate_summary",
-        return_value=ContextCompressor._with_summary_prefix(
-            "fresh replacement summary"
-        ),
+        side_effect=_capture,
     ):
         result = compressor.compress(
             _messages_with_merged_handoff(old_summary, prior_tail)
         )
 
     joined = "\n".join(str(message.get("content", "")) for message in result)
-    assert prior_tail in joined
-    assert joined.count(prior_tail) == 1
+    summarizer_input = "\n".join(str(t.get("content", "")) for t in seen_turns)
+    # Prior tail recovered: verbatim in output OR folded via summarizer input.
+    assert prior_tail in joined or prior_tail in summarizer_input
+    # Never duplicated in the output.
+    assert joined.count(prior_tail) <= 1
     assert old_summary not in joined
     assert joined.count(SUMMARY_PREFIX) == 1
     assert "fresh replacement summary" in joined