bug: Agent server stream-json parser crashes on non-dict JSON lines

[vybe]

Summary

The agent server's headless task stdout parser crashes when Claude Code emits a stream-json line that is a valid JSON string literal (not an object). This causes the entire execution to fail with "Task returned empty response" — discarding all work done during the session. Observed on a scheduled task that ran for ~9 minutes before the crash.

Component

Agent Server / claude_code.py / Headless Task stdout parser

Priority

P2

Error

ERROR:agent_server.services.claude_code:[Headless Task] Error reading stdout: 'str' object has no attribute 'get'

Downstream effect:

ERROR:services.task_execution_service:[TaskExecService] Failed to execute task on <agent>: Task returned empty response

Location

• File: src/agent-server/agent_server/services/claude_code.py
• Line: ~883 (in the _run_headless_with_streaming method)
• Function: stdout reading loop inside _run_headless_with_streaming

Root Cause

The stdout reading loop does:

raw_msg = json.loads(line.strip())       # line 877
raw_msg = sanitize_dict(raw_msg)          # line 879
...
if raw_msg.get("type") == "init" ...      # line 883

json.loads() can successfully parse a JSON string literal like "some text" into a Python str. The code then calls .get() on that string, which raises AttributeError: 'str' object has no attribute 'get'.

This AttributeError is caught by the broad except Exception as e at ~line 912, which logs the error and exits the stdout reading loop entirely — meaning all subsequent output (including the result message with cost/session data) is never processed. The execution is then recorded as failed with null cost, null session_id, and no response.

Reproduction Steps

1. Run a scheduled task that uses context: fork with a subagent (or any task where Claude Code emits a non-object JSON line in stream-json mode)
2. Observe the execution fails with "Task returned empty response"
3. Agent container logs show: Error reading stdout: 'str' object has no attribute 'get'

Suggested Fix

Add a type check after json.loads() to skip non-dict lines:

try:
    raw_msg = json.loads(line.strip())
    if not isinstance(raw_msg, dict):
        # stream-json can emit string literals; skip them
        continue
    raw_msg = sanitize_dict(raw_msg)
    raw_messages.append(raw_msg)
    ...

The same check should be added in process_stream_line() (line ~276) for defense in depth, though the primary fix in the stdout loop would prevent the crash.

Additionally, sanitize_dict() should handle non-dict input gracefully.

Environment

• Trinity version: 0523ccd
• Agent server: built into agent container image

Related

• src/agent-server/agent_server/services/claude_code.py — both _run_headless_with_streaming and process_stream_line
• parse_stream_json_output() (line 124) has the same pattern but already returns early on JSONDecodeError; it still calls .get() without checking type