Completes the #90953 salvage on post-#98237 main:
- New _merge_request_overrides helper defines the precedence contract:
explicit delegation.request_overrides merges OVER runtime/parent-derived
overrides — explicit top-level keys win; extra_body is deep-merged one
level so runtime extra_body keys survive unless redefined. Inputs are
copy.deepcopy'd so transport-side mutation can't leak into config or the
provider runtime cache.
- Direct base_url branch: explicit key now merges over the #98237
provider-alongside-base_url runtime overrides instead of being a separate
return shape; max_output_tokens preserved.
- Named-provider branch and parent-inherit branch now honor the key too, so
delegation.request_overrides never silently no-ops.
- _build_child_agent honors override_request_overrides whenever set
(previously only when override_provider was set), enabling the inherit
branch's merged value to reach the child.
- DEFAULT_CONFIG: delegation.request_overrides entry with comment.
- Tests: expanded tests/tools/test_delegate_request_overrides.py — deep-copy
proofs, explicit-over-runtime precedence on the provider-alongside-base_url
path, named-provider branch, inherit branch, and merge-helper unit tests.
- Docs: configuration.md delegation section + features/delegation.md document
the key, precedence, and example YAML (OpenRouter extra_body.provider.sort).
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