Two related bugs caused subagent delegation to silently return empty summaries
with 0 tokens when the user configured delegation.provider=bedrock alongside
delegation.base_url=https://bedrock-runtime.<region>.amazonaws.com.
Root cause #1 — misrouting in _resolve_delegation_credentials():
The configured_base_url branch unconditionally forced provider='custom' and
api_mode='chat_completions', only specializing for chatgpt.com, anthropic,
and kimi hosts. Bedrock (and other native-SDK providers) fell through as
'custom' + chat_completions, which then POSTed OpenAI-shaped JSON at
Bedrock's native API. Bedrock rejected the payload and returned nothing,
which looked like an empty LLM response to the child agent.
Fix: when provider is one of {bedrock, vertex, google, google-genai}, skip
the base_url short-circuit and fall through to resolve_runtime_provider(),
which knows how to construct the proper SDK client. base_url can still be
forwarded through that path for regional overrides.
Root cause #2 — '(empty)' sentinel accepted as success:
After N retries of empty LLM responses, run_agent.py emits the literal
string '(empty)' as final_response. _run_single_child then hit
`elif summary:` — '(empty)' is truthy, so status became 'completed' and
the parent surfaced a blank result with no error. Users saw api_calls=4,
tokens=0, duration~0.4s, status=completed.
Fix: treat final_response.strip() == '(empty)' as a failure so the parent
surfaces it instead of silently accepting zero-content 'success'.
Both paths were reproduced in a live Hermes TUI session on us-west-2 Bedrock
(provider=bedrock, model=us.anthropic.claude-sonnet-4-6) and are covered by
new tests in tests/tools/test_delegate.py.
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