diff --git a/agent/protocol/agent_stream.py b/agent/protocol/agent_stream.py
index 49050a6b..26f6fd49 100644
--- a/agent/protocol/agent_stream.py
+++ b/agent/protocol/agent_stream.py
@@ -196,6 +196,11 @@ class AgentStreamExecutor:
         # are never stripped mid-execution (which would cause LLM loops).
         self._trim_messages()
 
+        # Validate after trimming: trimming may leave orphaned tool_use at the
+        # boundary (e.g. the last kept turn ends with an assistant tool_use whose
+        # tool_result was in a discarded turn).
+        self._validate_and_fix_messages()
+
         self._emit_event("agent_start")
 
         final_response = ""
diff --git a/agent/protocol/message_utils.py b/agent/protocol/message_utils.py
index 3215ed48..8c9f4fc7 100644
--- a/agent/protocol/message_utils.py
+++ b/agent/protocol/message_utils.py
@@ -70,67 +70,71 @@ def sanitize_claude_messages(messages: List[Dict]) -> int:
         else:
             break
 
-    # 3. Full scan: ensure every tool_result references a known tool_use id
-    known_ids: Set[str] = set()
-    i = 0
-    while i < len(messages):
-        msg = messages[i]
-        role = msg.get("role")
-        content = msg.get("content", [])
+    # 3. Iteratively remove unmatched tool_use / tool_result until stable.
+    #    Removing one broken message can orphan others (e.g. an assistant msg
+    #    with both matched and unmatched tool_use — deleting it orphans the
+    #    previously-matched tool_result).  Loop until clean.
+    for _ in range(5):
+        use_ids: Set[str] = set()
+        result_ids: Set[str] = set()
+        for msg in messages:
+            for block in (msg.get("content") or []):
+                if not isinstance(block, dict):
+                    continue
+                if block.get("type") == "tool_use" and block.get("id"):
+                    use_ids.add(block["id"])
+                elif block.get("type") == "tool_result" and block.get("tool_use_id"):
+                    result_ids.add(block["tool_use_id"])
 
-        if role == "assistant" and isinstance(content, list):
-            for block in content:
-                if isinstance(block, dict) and block.get("type") == "tool_use":
-                    tid = block.get("id", "")
-                    if tid:
-                        known_ids.add(tid)
+        bad_use = use_ids - result_ids
+        bad_result = result_ids - use_ids
+        if not bad_use and not bad_result:
+            break
 
-        elif role == "user" and isinstance(content, list):
-            if not _has_block_type(content, "tool_result"):
+        pass_removed = 0
+        i = 0
+        while i < len(messages):
+            msg = messages[i]
+            role = msg.get("role")
+            content = msg.get("content", [])
+            if not isinstance(content, list):
                 i += 1
                 continue
 
-            orphaned = [
-                b.get("tool_use_id", "")
-                for b in content
-                if isinstance(b, dict)
-                and b.get("type") == "tool_result"
-                and b.get("tool_use_id", "")
-                and b.get("tool_use_id", "") not in known_ids
-            ]
-            if orphaned:
-                orphaned_set = set(orphaned)
-                if not _has_block_type(content, "text"):
-                    logger.warning(
-                        f"⚠️ Removing orphaned tool_result message (tool_ids: {orphaned})"
-                    )
-                    messages.pop(i)
-                    removed += 1
-                    # Also remove a preceding broken assistant tool_use message
-                    if i > 0 and messages[i - 1].get("role") == "assistant":
-                        prev = messages[i - 1].get("content", [])
-                        if isinstance(prev, list) and _has_block_type(prev, "tool_use"):
-                            messages.pop(i - 1)
-                            removed += 1
-                            i -= 1
-                    continue
-                else:
-                    new_content = [
-                        b for b in content
-                        if not (
-                            isinstance(b, dict)
-                            and b.get("type") == "tool_result"
-                            and b.get("tool_use_id", "") in orphaned_set
-                        )
-                    ]
-                    delta = len(content) - len(new_content)
-                    if delta:
-                        logger.warning(
-                            f"⚠️ Stripped {delta} orphaned tool_result block(s) from mixed message"
-                        )
-                        msg["content"] = new_content
-                        removed += delta
-        i += 1
+            if role == "assistant" and bad_use and any(
+                isinstance(b, dict) and b.get("type") == "tool_use"
+                and b.get("id") in bad_use for b in content
+            ):
+                logger.warning(f"⚠️ Removing assistant msg with unmatched tool_use")
+                messages.pop(i)
+                pass_removed += 1
+                continue
+
+            if role == "user" and bad_result and _has_block_type(content, "tool_result"):
+                has_bad = any(
+                    isinstance(b, dict) and b.get("type") == "tool_result"
+                    and b.get("tool_use_id") in bad_result for b in content
+                )
+                if has_bad:
+                    if not _has_block_type(content, "text"):
+                        logger.warning(f"⚠️ Removing user msg with unmatched tool_result")
+                        messages.pop(i)
+                        pass_removed += 1
+                        continue
+                    else:
+                        before = len(content)
+                        msg["content"] = [
+                            b for b in content
+                            if not (isinstance(b, dict) and b.get("type") == "tool_result"
+                                    and b.get("tool_use_id") in bad_result)
+                        ]
+                        pass_removed += before - len(msg["content"])
+
+            i += 1
+
+        removed += pass_removed
+        if pass_removed == 0:
+            break
 
     if removed:
         logger.info(f"🔧 Message validation: removed {removed} broken message(s)")