## Description
The compression-pipeline timeout was hard-coded at 30s, so slow CPUs and
long Claude Code conversations had no recourse. #946 asks to wire
`HEADROOM_COMPRESSION_TIMEOUT_SECONDS` through. Refs #946.
## Type of Change
- [x] New feature (non-breaking change that adds functionality)
## Changes Made
- Read `HEADROOM_COMPRESSION_TIMEOUT_SECONDS` from the environment
(float), falling back to 30 on an unparseable value.
## Testing
- [x] Unit tests pass (`pytest`)
- [x] New tests added for new functionality
### Test Output
```text
$ pytest tests/test_proxy/test_compression_timeout_config.py -q
4 passed in 0.09s
```
## Real Behavior Proof
- Environment: Linux, Python 3.13, editable build of this branch
- Exact command / steps: `HEADROOM_COMPRESSION_TIMEOUT_SECONDS=88 python
-c "import headroom.proxy.helpers as h;
print(h.COMPRESSION_TIMEOUT_SECONDS)"`
- Observed result: prints `88.0` (default `30.0`; an unparseable value
falls back to `30.0`)
- Not tested: a live compression actually exceeding the configured
timeout under real load
## Review Readiness
- [x] I have performed a self-review
- [x] This PR is ready for human review
---------
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
