## Description
Fixes#2504. `CostTracker.estimate_cost` runs on the per-request cost
path and logs a WARNING whenever LiteLLM can't price the model:
```python
except Exception as e:
logger.warning(f"Failed to get pricing for model {model}: {e}")
return None
```
For a custom / OpenAI-compatible model LiteLLM can't resolve (e.g.
`glm-5.2` via `--backend anyllm --anyllm-provider openai`), this fires
on **every single request**, flooding `proxy.log` with hundreds of
identical lines and burying genuinely useful warnings. The `LiteLLM not
available` branch above it has the same per-request flooding shape.
## Fix
Track already-warned models in a small module-level set and emit each
pricing-failure warning (and the LiteLLM-unavailable warning) once per
process. The set is bounded by the number of distinct model names seen.
No new dependencies or config. The cost result itself is unchanged
(`None` on failure); only the log volume changes.
## Type of Change
- [x] Bug fix (non-breaking change that fixes an issue)
- [ ] New feature (non-breaking change that adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
- [ ] Performance improvement
- [ ] Code refactoring (no functional changes)
## Changes Made
- `headroom/proxy/cost.py`: add a module-level `_warned_pricing_models`
set and `_warn_pricing_once` helper; route the pricing-failure and
LiteLLM-unavailable warnings in `estimate_cost` through it.
- `tests/test_cost_pricing_warning_dedup.py` (new): assert a repeated
unresolvable model warns once, distinct models each warn once, and the
LiteLLM-unavailable warning is deduped too.
## Testing
- [x] Unit tests pass (`pytest`)
- [x] Linting passes (`ruff check .`)
- [x] Type checking passes (`mypy headroom`)
- [x] New tests added for new functionality
- [ ] Manual testing performed
### Test Output
```text
$ python -m pytest tests/test_cost_pricing_warning_dedup.py -q
3 passed
# with the fix reverted, the module-level set does not exist, so the
# dedup tests error/fail (the pre-fix code warned once per request)
$ uvx ruff@0.15.17 check headroom/proxy/cost.py tests/test_cost_pricing_warning_dedup.py
All checks passed!
$ uvx mypy@1.20.2 --ignore-missing-imports headroom/proxy/cost.py
Success: no issues found in 1 source file
```
## Real Behavior Proof
- Environment: Windows 11, Python 3.12, project venv (`uv sync --extra
proxy`), `uvx ruff@0.15.17` / `uvx mypy@1.20.2`, pytest in the venv.
- Exact command / steps: monkeypatched `_get_litellm_module` to a stub
whose `cost_per_token` raises (and, separately, to `None`), called
`CostTracker.estimate_cost("glm-5.2", ...)` five times and two distinct
unresolvable models twice each, capturing `headroom.proxy` WARNING
records with `caplog`.
- Observed result: with the fix each model produces exactly one `Failed
to get pricing for model ...` warning (and one `LiteLLM not available
...`) regardless of call count; the pre-fix code logged one per call.
`estimate_cost` still returns `None` on failure. Ran against the actual
module.
- Not tested: a live multi-request session against a real unpriced model
end to end.
## Review Readiness
- [x] I have performed a self-review
- [x] This PR is ready for human review
## Checklist
- [x] My code follows the project's style guidelines
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] I have updated the CHANGELOG.md if applicable
