Summary

• preserve concrete delegation.provider routing when delegation.base_url/api_key are set
• pass delegation endpoint/key as explicit runtime provider overrides instead of relabeling provider-specific children as custom
• expand \ references from runtime CLI_CONFIG delegation settings
• add regression coverage for DeepSeek subagent overrides and parent ACP transport clearing

Fixes #26482

Tests

• python -m pytest -o addopts= tests\tools\test_delegate.py -q --tb=short
• python -m pytest -o addopts= tests\e2e\test_discord_adapter.py -q --tb=short
• python -m pytest -o addopts= tests\run_agent\test_provider_parity.py::TestDeveloperRoleSwap::test_developer_role_via_nous_portal tests\run_agent\test_provider_parity.py::TestBuildApiKwargsNousPortal::test_includes_nous_product_tags tests\run_agent\test_provider_parity.py::TestBuildApiKwargsNousPortal::test_uses_chat_completions_format -q --tb=short
• python -m ruff check tools\delegate_tool.py tests\tools\test_delegate.py tests\e2e\conftest.py tests\run_agent\test_provider_parity.py
• git diff --check