diff --git a/nanobot/agent/memory.py b/nanobot/agent/memory.py
index 0bad5125a..943d91855 100644
--- a/nanobot/agent/memory.py
+++ b/nanobot/agent/memory.py
@@ -400,6 +400,22 @@ class Consolidator:
 
         return last_boundary
 
+    def _cap_consolidation_boundary(
+        self,
+        session: Session,
+        end_idx: int,
+    ) -> int | None:
+        """Clamp the chunk size without breaking the user-turn boundary."""
+        start = session.last_consolidated
+        if end_idx - start <= self._MAX_CHUNK_MESSAGES:
+            return end_idx
+
+        capped_end = start + self._MAX_CHUNK_MESSAGES
+        for idx in range(capped_end, start, -1):
+            if session.messages[idx].get("role") == "user":
+                return idx
+        return None
+
     def estimate_session_prompt_tokens(self, session: Session) -> tuple[int, str]:
         """Estimate current prompt size for the normal session history view."""
         history = session.get_history(max_messages=0)
@@ -495,14 +511,19 @@ class Consolidator:
                     return
 
                 end_idx = boundary[0]
+                end_idx = self._cap_consolidation_boundary(session, end_idx)
+                if end_idx is None:
+                    logger.debug(
+                        "Token consolidation: no capped boundary for {} (round {})",
+                        session.key,
+                        round_num,
+                    )
+                    return
+
                 chunk = session.messages[session.last_consolidated:end_idx]
                 if not chunk:
                     return
 
-                if len(chunk) > self._MAX_CHUNK_MESSAGES:
-                    chunk = chunk[:self._MAX_CHUNK_MESSAGES]
-                    end_idx = session.last_consolidated + len(chunk)
-
                 logger.info(
                     "Token consolidation round {} for {}: {}/{} via {}, chunk={} msgs",
                     round_num,
diff --git a/tests/agent/test_consolidator.py b/tests/agent/test_consolidator.py
index 72968b0e1..b7989d9dd 100644
--- a/tests/agent/test_consolidator.py
+++ b/tests/agent/test_consolidator.py
@@ -76,3 +76,52 @@ class TestConsolidatorTokenBudget:
         consolidator.archive = AsyncMock(return_value=True)
         await consolidator.maybe_consolidate_by_tokens(session)
         consolidator.archive.assert_not_called()
+
+    async def test_chunk_cap_preserves_user_turn_boundary(self, consolidator):
+        """Chunk cap should rewind to the last user boundary within the cap."""
+        consolidator._SAFETY_BUFFER = 0
+        session = MagicMock()
+        session.last_consolidated = 0
+        session.key = "test:key"
+        session.messages = [
+            {
+                "role": "user" if i in {0, 50, 61} else "assistant",
+                "content": f"m{i}",
+            }
+            for i in range(70)
+        ]
+        consolidator.estimate_session_prompt_tokens = MagicMock(
+            side_effect=[(1200, "tiktoken"), (400, "tiktoken")]
+        )
+        consolidator.pick_consolidation_boundary = MagicMock(return_value=(61, 999))
+        consolidator.archive = AsyncMock(return_value=True)
+
+        await consolidator.maybe_consolidate_by_tokens(session)
+
+        archived_chunk = consolidator.archive.await_args.args[0]
+        assert len(archived_chunk) == 50
+        assert archived_chunk[0]["content"] == "m0"
+        assert archived_chunk[-1]["content"] == "m49"
+        assert session.last_consolidated == 50
+
+    async def test_chunk_cap_skips_when_no_user_boundary_within_cap(self, consolidator):
+        """If the cap would cut mid-turn, consolidation should skip that round."""
+        consolidator._SAFETY_BUFFER = 0
+        session = MagicMock()
+        session.last_consolidated = 0
+        session.key = "test:key"
+        session.messages = [
+            {
+                "role": "user" if i in {0, 61} else "assistant",
+                "content": f"m{i}",
+            }
+            for i in range(70)
+        ]
+        consolidator.estimate_session_prompt_tokens = MagicMock(return_value=(1200, "tiktoken"))
+        consolidator.pick_consolidation_boundary = MagicMock(return_value=(61, 999))
+        consolidator.archive = AsyncMock(return_value=True)
+
+        await consolidator.maybe_consolidate_by_tokens(session)
+
+        consolidator.archive.assert_not_awaited()
+        assert session.last_consolidated == 0