BUG: turn.output always empty on sequential team OTEL spans

[hbachala]

Des:
Sequential team execution emits turn.N spans with turn.member.name populated but turn.output always empty, even when the member produces a response.

1. Create 2 agents `Create two agents and a sequential team:

apiVersion: ark.mckinsey.com/v1alpha1
kind: Agent
metadata: { name: agent-a, namespace: default }
spec:
modelRef: { name: }
prompt: "You are Agent A. Reply with: I AM AGENT A"

apiVersion: ark.mckinsey.com/v1alpha1
kind: Agent
metadata: { name: agent-b, namespace: default }
spec:
modelRef: { name: }
prompt: "You are Agent B. Repeat what you were told."

apiVersion: ark.mckinsey.com/v1alpha1
kind: Team
metadata: { name: seq-team, namespace: default }
spec:
strategy: sequential
members:
- { name: agent-a, type: agent }
- { name: agent-b, type: agent }2. Submit a queryapiVersion: ark.mckinsey.com/v1alpha1
kind: Query
metadata: { name: repro-query, namespace: default }
spec:
input: "Say your name"
target: { name: seq-team, type: team }
type: user
timeout: 5m
ttl: 1h3. wait for status.phase == done 4. Fetch the trace from the broker curl -s "http://localhost:8082/v1/broker/traces?limit=20" |
python3 -c "
import json, sys
data = json.load(sys.stdin)
for trace in data['items']:
for span in trace['spans']:
if span['name'].startswith('turn.'):
attrs = {a['key']: list(a['value'].values())[0] for a in span.get('attributes', [])}
print(span['name'], '→ turn.output:', repr(attrs.get('turn.output', '')))
"`

Expected: turn.output contains the agent's response text
Actual: turn.output is '' (empty string) or missing