What does this PR do?

Fixes the OpenRouter auxiliary client fallback path so a cooled-down/exhausted credential pool no longer blocks OPENROUTER_API_KEY from being used. This keeps auxiliary tasks on the expected env-var fallback path instead of returning (None, None) early.

Related Issue

Fixes #23452

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• update agent/auxiliary_client.py so _try_openrouter() only returns the pool-backed client when a usable pooled key exists
• fall through to OPENROUTER_API_KEY env lookup when the pool exists but currently has no selectable entry
• add a regression test in tests/agent/test_auxiliary_client.py covering the exhausted-pool + env-fallback case

How to Test

1. uv run --frozen pytest -q -o addopts='' tests/agent/test_auxiliary_client.py -k 'openrouter and (pool_exhausted or env_keeps_not_set_warning or falls_back_to_env)'
2. uv run --frozen ruff check agent/auxiliary_client.py tests/agent/test_auxiliary_client.py
3. env -i HOME="$HOME" PATH="$PATH" TERM="${TERM:-xterm-256color}" UV_CACHE_DIR="$HOME/.cache/uv" uv run --frozen pytest -q -o addopts='' --collect-only tests/agent/test_auxiliary_client.py -k 'openrouter and (pool_exhausted or env_keeps_not_set_warning or falls_back_to_env)'

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: macOS 15.x

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

Screenshots / Logs

• targeted pytest: 4 passed, 138 deselected
• ruff check: passed
• collect-only smoke: 4 tests collected
• repo-wide pytest tests/ -q was not used as the merge gate here because the same clean origin/main baseline currently shows unrelated collection failures outside this change scope