fix(openhands): handle none content in token estimates (#612)

Closes #607. Assistant tool-call turns can carry content=None, which crashed token estimation (len(m.content)) and think-tag stripping. Normalize with 'content or ""', route native OpenHands truncation through the shared estimate_prompt_tokens, and add tests for the estimator, the truncation helper, and an end-to-end tool-call run with None content.

src/openjarvis/agents/native_openhands.py

@@ -19,6 +19,7 @@ from openjarvis.agents.prompt_loader import (
 from openjarvis.core.events import EventBus
 from openjarvis.core.registry import AgentRegistry
 from openjarvis.core.types import Message, Role, ToolCall, ToolResult
+from openjarvis.engine._base import estimate_prompt_tokens
 from openjarvis.engine._stubs import InferenceEngine
 from openjarvis.tools._stubs import BaseTool, build_tool_descriptions
 
@@ -116,8 +117,7 @@ class NativeOpenHandsAgent(ToolUsingAgent):
         max_prompt_tokens: int = 3000,
     ) -> list[Message]:
         """Truncate messages if estimated token count exceeds limit."""
-        total_chars = sum(len(m.content) for m in messages)
-        estimated_tokens = total_chars // 4
+        estimated_tokens = estimate_prompt_tokens(messages)
         if estimated_tokens <= max_prompt_tokens:
             return messages
         # Find the last user message and truncate its content
@@ -125,7 +125,7 @@ class NativeOpenHandsAgent(ToolUsingAgent):
             if messages[i].role == Role.USER:
                 excess_tokens = estimated_tokens - max_prompt_tokens
                 excess_chars = excess_tokens * 4
-                original = messages[i].content
+                original = messages[i].content or ""
                 if len(original) > excess_chars + 200:
                     truncated = original[: len(original) - excess_chars]
                     messages[i] = Message(
@@ -258,7 +258,7 @@ class NativeOpenHandsAgent(ToolUsingAgent):
                 # still emitted before re-raising.
                 self._emit_turn_end(turns=1, error=True)
                 raise
-            content = self._strip_think_tags(result.get("content", ""))
+            content = self._strip_think_tags(result.get("content") or "")
             usage = result.get("usage", {})
             self._emit_turn_end(turns=1)
             return AgentResult(
@@ -315,7 +315,7 @@ class NativeOpenHandsAgent(ToolUsingAgent):
             for k in total_usage:
                 total_usage[k] += usage.get(k, 0)
 
-            content = result.get("content", "")
+            content = result.get("content") or ""
             # Strip think tags so they don't interfere with parsing
             content = self._strip_think_tags(content)
             last_content = content

src/openjarvis/engine/_base.py

@@ -55,7 +55,7 @@ def estimate_prompt_tokens(messages: Sequence[Message]) -> int:
     Uses ~4 characters per token (standard BPE average for English) plus
     a small per-message overhead for role markers and separators.
     """
-    total_chars = sum(len(m.content) for m in messages)
+    total_chars = sum(len(m.content or "") for m in messages)
     # ~4 tokens overhead per message for role markers / separators
     overhead = len(messages) * 4
     return max(1, total_chars // 4 + overhead)

tests/agents/test_native_openhands.py

@@ -8,7 +8,7 @@ from openjarvis.agents._stubs import AgentContext
 from openjarvis.agents.native_openhands import NativeOpenHandsAgent
 from openjarvis.core.events import EventBus, EventType
 from openjarvis.core.registry import AgentRegistry
-from openjarvis.core.types import Conversation, Message, Role, ToolResult
+from openjarvis.core.types import Conversation, Message, Role, ToolCall, ToolResult
 from openjarvis.tools._stubs import BaseTool, ToolSpec
 
 # ---------------------------------------------------------------------------
@@ -118,6 +118,51 @@ class TestNativeOpenHandsRegistration:
 
 
 class TestNativeOpenHandsAgent:
+    def test_truncate_handles_none_content_tool_call_turn(self):
+        """Tool-call assistant turns may carry content=None."""
+        engine = MagicMock()
+        engine.engine_id = "mock"
+        agent = NativeOpenHandsAgent(engine, "test-model")
+        messages = [
+            Message(role=Role.USER, content="hi"),
+            Message(
+                role=Role.ASSISTANT,
+                content=None,  # type: ignore[arg-type]
+                tool_calls=[ToolCall(id="call_1", name="calculator", arguments="{}")],
+            ),
+        ]
+
+        assert agent._truncate_if_needed(messages) == messages
+
+    def test_native_tool_call_with_none_content_does_not_crash(self):
+        """Native tool-call responses may omit assistant text content."""
+        engine = MagicMock()
+        engine.engine_id = "mock"
+        engine.generate.side_effect = [
+            _engine_response(
+                None,
+                tool_calls=[
+                    {
+                        "id": "call_1",
+                        "name": "calculator",
+                        "arguments": '{"expression": "2+2"}',
+                    }
+                ],
+            ),
+            _engine_response("The result is 4."),
+        ]
+        agent = NativeOpenHandsAgent(
+            engine,
+            "test-model",
+            tools=[_CalculatorStub()],
+        )
+
+        result = agent.run("What is 2+2?")
+
+        assert result.content == "The result is 4."
+        assert result.turns == 2
+        assert [tr.content for tr in result.tool_results] == ["4"]
+
     def test_simple_response(self):
         """No code -> direct answer."""
         engine = MagicMock()

tests/engine/test_base.py

@@ -0,0 +1,17 @@
+from __future__ import annotations
+
+from openjarvis.core.types import Message, Role, ToolCall
+from openjarvis.engine._base import estimate_prompt_tokens
+
+
+def test_estimate_prompt_tokens_handles_none_content_tool_call_turn() -> None:
+    messages = [
+        Message(role=Role.USER, content="hi"),
+        Message(
+            role=Role.ASSISTANT,
+            content=None,  # type: ignore[arg-type]
+            tool_calls=[ToolCall(id="call_1", name="lookup", arguments="{}")],
+        ),
+    ]
+
+    assert estimate_prompt_tokens(messages) == 8