Adds an opt-in compression interceptor that buffers Anthropic
/v1/messages requests, runs IntelligentContextManager over the
messages array, and forwards the (possibly trimmed) body upstream.
All other paths, methods, and content-types stay on the original
streaming passthrough — so existing operators see zero change.
Behaviour gates ALL must be true to buffer + compress:
- --compression flag (or HEADROOM_PROXY_COMPRESSION=1)
- method == POST
- path == /v1/messages
- Content-Type: application/json
- ICM constructed successfully at startup
Falls through to streaming on any failure: parse, missing fields,
unknown model, body-too-large. Compression must never break a
request — that's the safety contract.
Model context windows come from a vendored LiteLLM snapshot at
crates/headroom-proxy/data/model_prices_and_context_window.json
parsed once into an OnceLock<HashMap>. Refresh via
scripts/refresh_model_limits.sh. Rationale documented inline:
hardcoded tables silently rot; LiteLLM is the canonical source
the entire LLM-tooling ecosystem relies on.
New tests:
- 16 unit tests across compression::{anthropic, icm, model_limits}
- 5 integration tests: off-passthrough, on-short-passthrough,
on-oversized-trim, on-non-json-skip, on-non-llm-path-skip
Verification:
- cargo test --workspace -> 884 passed, 0 failed
- cargo clippy --workspace -- -D warnings -> clean
- cargo fmt --check -> clean
