Claude Code Provider Does Not Capture Response Text — HarnessResult.result is always 'None' due to Incorrect Message Type Check

[Sridhar-Vetrivel]

Describe the bug

Bug Report: result.text Always Returns Empty
Summary
The Claude Code provider (sdk/python/agentfield/harness/providers/claude.py) never captures the response text, so HarnessResult.result is always None and result.text always returns "". This test case is for basic prompt, without schema.
Root Cause
The provider waits for a message with type == "result", but the Claude Agent SDK never sends that. Instead, it sends a message with subtype == "success" (no type field). Because the condition never matches, result_text stays None.
In the output messages you can see:
{'subtype': 'success', ..., 'result': "Here's a simple Python function..."}
There is no type field here — only subtype.

Steps to reproduce

1. Create a python file(TC-01.py)
   '''
   Test Case: TC-01
   Description: Test basic functionality of the harness with a simple math question.
   Basic Prompt, no schema
   Verify .harness() returns a HarnessResult with .text set and no error.
   '''

import asyncio
from agentfield import Agent
from agentfield.types import HarnessConfig

async def test():
    agent = Agent(
        node_id="test-basic",
        harness_config=HarnessConfig(provider="claude-code"),
        auto_register=False,
    )
    result = await agent.harness(
        "Write a python function that adds two numbers (2, 2) together and return the result."
    )
    print("HarnessResult:",result)
    print("is_error:", result.is_error)
    print("text:", result.text)  # <-- Returning None, which is unexpected
    # print("message:", result.messages)
    print("num_turns:", result.num_turns)
    print("duration_ms:", result.duration_ms)
    assert not result.is_error
    print("PASS")

asyncio.run(test())

2. Run 'python TC-01.py' in the terminal

3. Sample Output
   !!!Ensure the final result is printed to stdout for harness capture None <--- This line is printed from claude.py which I have written as print statement to find out and verify the issue.
   HarnessResult: HarnessResult(result=None, parsed=None, is_error=False, ......,
   messages=[{'subtype': 'init', 'data': {'type': 'system', 'subtype': 'init', 'cwd': '/home/sridharvetrivel/harness-test', 'session_id': '27ad48b4-fdab-4384-ab22-dc53dff12be6', 'tools': ['Task', 'TaskOutput', 'Bash', 'Glob', 'Grep', 'ExitPlanMode', 'Read', 'Edit', 'Write', 'NotebookEdit', 'WebFetch', 'TodoWrite', 'WebSearch', 'TaskStop', 'AskUserQuestion', 'Skill', 'EnterPlanMode', 'EnterWorktree', 'CronCreate', 'CronDelete', 'CronList', 'ToolSearch'], 'mcp_servers': [{'name': 'claude.ai Gmail', 'status': 'needs-auth'}, {'name': 'claude.ai Google Calendar', 'status': 'needs-auth'}, {'name': 'claude.ai Hugging Face', 'status': 'needs-auth'}], 'model': 'claude-sonnet-4-6', 'permissionMode': 'default', 'slash_commands': ['keybindings-help', 'debug', 'simplify', 'batch', 'loop', 'claude-api', 'compact', 'context', 'cost', 'heapdump', 'init', 'pr-comments', 'release-notes', 'review', 'security-review', 'extra-usage', 'insights'], 'apiKeySource': 'none', 'claude_code_version': '2.1.71', 'output_style': 'default', 'agents': ['general-purpose', 'statusline-setup', 'Explore', 'Plan'], 'skills': ['keybindings-help', 'debug', 'simplify', 'batch', 'loop', 'claude-api'], 'plugins': [], 'uuid': '063471bc-0d16-4406-9e5f-dc82f16e56ee', 'fast_mode_state': 'off'}}, {'content': [ThinkingBlock(thinking='Simple Python function request.', signature='eysks....')], 'model': 'claude-sonnet-4-6', 'parent_tool_use_id': None, 'error': None}, {'content': [TextBlock(text="Here's a simple Python function that adds two numbers together:\n\npython\ndef add_numbers(a, b):\n return a + b\n\nresult = add_numbers(2, 2)\nprint(result) # Output: 4\n\n\nBreakdown:\n- add_numbers(a, b) — defines the function with two parameters.\n- return a + b — adds the two numbers and returns the result.\n- add_numbers(2, 2) — calls the function with 2 and 2, returning 4.")], 'model': 'claude-sonnet-4-6', 'parent_tool_use_id': None, 'error': None}, {'subtype': 'success', 'duration_ms': 2807, 'duration_api_ms': 2792, 'is_error': False, 'num_turns': 1, 'session_id': '27ad48b4-fdab-4384-ab22-dc53dff12be6', 'stop_reason': 'end_turn', 'total_cost_usd': 0.008761999999999999, 'usage': {'input_tokens': 3, 'cache_creation_input_tokens': 0, 'cache_read_input_tokens': 9944, 'output_tokens': 151, 'server_tool_use': {'web_search_requests': 0, 'web_fetch_requests': 0}, 'service_tier': 'standard', 'cache_creation': {'ephemeral_1h_input_tokens': 0, 'ephemeral_5m_input_tokens': 0}, 'inference_geo': '', 'iterations': [], 'speed': 'standard'}, 'result': "Here's a simple Python function that adds two numbers together:\n\npython\ndef add_numbers(a, b):\n return a + b\n\nresult = add_numbers(2, 2)\nprint(result) # Output: 4\n\n\nBreakdown:\n- add_numbers(a, b) — defines the function with two parameters.\n- return a + b — adds the two numbers and returns the result.\n- add_numbers(2, 2) — calls the function with 2 and 2, returning 4.", 'structured_output': None}])
   is_error: False
   text:
   num_turns: 0
   duration_ms: 5529
   PASS

Expected behavior

text: null <-- This should display the response provided by the LLM
text: Here's a simple Python function that adds two numbers together:

def add_two_numbers(a, b):
    return a + b

result = add_two_numbers(2, 2)
print(result)  # Output: 4

How it works:

• add_two_numbers(a, b) — takes two parameters, a and b
• return a + b — adds them together and returns the result
• Calling it with (2, 2) returns 4

Environment

AgentField Control Plane
  Version:    0.1.48-rc.2
  Commit:     881b1aa
  Built:      2026-03-09T07:26:01Z
  Go version: go1.24.2
  OS/Arch:    linux/amd64

Additional context

This test case is for basic prompt, Without schema.

[github-actions]

Thanks for picking this up, @AbirAbbas! 🎉

Here's what to expect:

• We'll check in after 7 days if we haven't heard an update
• After 14 days, we'll send a second reminder
• After 21 days without activity, we'll unassign to let others contribute

Tips for success:

• Drop a comment when you start working on it
• Share any blockers - we're here to help!
• Link your PR with Fixes #252 in the description

Happy coding! 🚀