fix(session): never persist tool results without a declared tool call

nanobot/agent/loop.py

@@ -1577,6 +1577,13 @@ class AgentLoop:
         """Save new-turn messages into session, truncating large tool results."""
         from datetime import datetime
 
+        declared_tool_call_ids = {
+            str(tc["id"])
+            for m in session.messages
+            if m.get("role") == "assistant"
+            for tc in m.get("tool_calls") or []
+            if isinstance(tc, dict) and tc.get("id")
+        }
         last_assistant_idx: int | None = None
         for m in messages[skip:]:
             entry = dict(m)
@@ -1584,6 +1591,17 @@ class AgentLoop:
             if role == "assistant" and not content and not entry.get("tool_calls"):
                 continue  # skip empty assistant messages — they poison session context
             if role == "tool":
+                tool_call_id = entry.get("tool_call_id")
+                if tool_call_id and str(tool_call_id) not in declared_tool_call_ids:
+                    # A tool result without a declared call violates the
+                    # OpenAI/Anthropic pairing contract and would poison
+                    # every future request built from this session (#4006).
+                    logger.warning(
+                        "Dropping orphaned tool result {} from session {} during persistence",
+                        tool_call_id,
+                        session.key,
+                    )
+                    continue
                 if isinstance(content, str) and len(content) > self.max_tool_result_chars:
                     entry["content"] = truncate_text_fn(content, self.max_tool_result_chars)
                 elif isinstance(content, list):
@@ -1613,6 +1631,11 @@ class AgentLoop:
             session.messages.append(entry)
             if role == "assistant":
                 last_assistant_idx = len(session.messages) - 1
+                declared_tool_call_ids.update(
+                    str(tc["id"])
+                    for tc in entry.get("tool_calls") or []
+                    if isinstance(tc, dict) and tc.get("id")
+                )
         if turn_latency_ms is not None and last_assistant_idx is not None:
             session.messages[last_assistant_idx]["latency_ms"] = int(turn_latency_ms)
         session.updated_at = datetime.now()

tests/agent/test_loop_save_turn.py

@@ -286,11 +286,22 @@ def test_save_turn_keeps_tool_results_under_16k() -> None:
 
     loop._save_turn(
         session,
-        [{"role": "tool", "tool_call_id": "call_1", "name": "read_file", "content": content}],
+        [
+            {
+                "role": "assistant",
+                "content": "",
+                "tool_calls": [{
+                    "id": "call_1",
+                    "type": "function",
+                    "function": {"name": "read_file", "arguments": "{}"},
+                }],
+            },
+            {"role": "tool", "tool_call_id": "call_1", "name": "read_file", "content": content},
+        ],
         skip=0,
     )
 
-    assert session.messages[0]["content"] == content
+    assert session.messages[1]["content"] == content
 
 
 def test_save_turn_stamps_latency_on_last_assistant() -> None:
@@ -1374,3 +1385,46 @@ def test_save_turn_keeps_placeholder_for_empty_tool_result_blocks() -> None:
     assert session.messages[1]["content"] == [
         {"type": "text", "text": "[tool result omitted during persistence]"}
     ]
+
+
+def test_save_turn_drops_orphaned_tool_results() -> None:
+    # Defense in depth for #4006: whatever upstream bug produces a tool
+    # result whose call was never declared, it must not reach history.
+    loop = _mk_loop()
+    session = Session(key="test:orphan-guard")
+    session.add_message("user", "hi")
+
+    loop._save_turn(
+        session,
+        [
+            {"role": "tool", "tool_call_id": "call_ghost", "name": "exec", "content": "boo"},
+            {"role": "assistant", "content": "done"},
+        ],
+        skip=0,
+    )
+
+    assert [m["role"] for m in session.messages] == ["user", "assistant"]
+
+
+def test_save_turn_keeps_tool_results_declared_in_prior_history() -> None:
+    # Declarations may live in already-persisted history (e.g. a restored
+    # runtime checkpoint), not only in the new-turn slice.
+    loop = _mk_loop()
+    session = Session(key="test:prior-declared")
+    session.add_message(
+        "assistant",
+        "working",
+        tool_calls=[{
+            "id": "call_prior",
+            "type": "function",
+            "function": {"name": "exec", "arguments": "{}"},
+        }],
+    )
+
+    loop._save_turn(
+        session,
+        [{"role": "tool", "tool_call_id": "call_prior", "name": "exec", "content": "ok"}],
+        skip=0,
+    )
+
+    assert [m["role"] for m in session.messages] == ["assistant", "tool"]