The subagent execution path did not call inject_langfuse_metadata(...)
and built its model with attach_tracing=True, so subagent LLM/tool
spans landed in Langfuse as isolated top-level traces carrying fresh
session ids and the default user. They were findable in the unfiltered
trace list but did not group under the parent thread's session card,
and Langfuse cost attribution for subagent traffic did not line up
with the parent conversation — even though DeerFlow's internal token
accounting (SubagentTokenCollector) was already correct.
Extend the lead-agent tracing wiring to the subagent path so a single
subagent run produces one trace that shares the parent thread's
session_id and user_id, with a subagent:<name> trace name:
- subagents/executor.py: append build_tracing_callbacks() output to
run_config["callbacks"] (preserving SubagentTokenCollector) and
call inject_langfuse_metadata(...) with thread_id, user_id, and
the normalized subagent:<name> trace name. Build the model with
attach_tracing=False so model-level tracing does not double-count
with the graph-root callbacks — the same pairing the lead agent
uses.
- tools/builtins/task_tool.py: resolve user_id via
resolve_runtime_user_id(runtime) at the parent tool layer (before
the background thread starts) and thread it through
SubagentExecutor.__init__, because the _current_user contextvar
is not guaranteed to survive the _execution_pool boundary.
Trace topology is unchanged: subagent traces remain separate top-level
traces in the same session, not nested as child spans under the lead
trace (Plan B follow-up).
Tests: tests/test_subagent_executor.py::TestSubagentTracingWiring
covers the callback append, the session/user/trace-name injection,
the disabled-langfuse no-op, the DEFAULT_USER_ID fallback, the
empty-name trace-name fallback, and the env-tag emission. Existing
test_create_agent_threads_explicit_app_config_to_model_and_middlewares
now also asserts attach_tracing=False.
Docs: CLAUDE.md Tracing System section documents subagents/executor.py
as a third injection point alongside worker.py and client.py.
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