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Author	SHA1	Message	Date
Tejas Chopra	6904d47a01	feat(proxy): hot-reload live env knobs so a reused proxy picks them up without a restart (#1090) ... ## Description A small class of env vars is read by the proxy **live, per request** — the output-shaper family (`HEADROOM_OUTPUT_SHAPER`, `HEADROOM_VERBOSITY_LEVEL`, `HEADROOM_EFFORT_ROUTER`, `HEADROOM_MECHANICAL_EFFORT`, `HEADROOM_VERBOSITY_AUTOTUNE`, `HEADROOM_OUTPUT_HOLDOUT`), or captured at import (`HEADROOM_INTERCEPT_READ_MIN_CHARS`). The proxy reads them from its own process environment, fixed at launch. But `headroom wrap` reuses an already-running proxy (it restarts only on startup-config drift), so a value exported *after* the proxy started silently no-op'd — e.g. `export HEADROOM_OUTPUT_SHAPER=1` had zero effect on a reused proxy on `:8787`. This PR makes those live knobs **hot-reloadable**: `headroom wrap` pushes them to the running proxy, which applies them in memory — no restart (a restart would cold-start the ML stack, drop in-flight requests, and lose CCR/router caches). _No linked issue._ ## Type of Change - [x] Bug fix (non-breaking change that fixes an issue) - [x] New feature (non-breaking change that adds functionality) - [ ] Breaking change (fix or feature that would cause existing functionality to change) - [x] Documentation update - [ ] Performance improvement - [ ] Code refactoring (no functional changes) ## Changes Made - `headroom/proxy/runtime_env.py` (new): single source of truth registering the live knobs + a thread-safe process-global override store. `getenv()` (override-then-env) is a drop-in for `os.environ.get`; behaviour is byte-identical when no override is set. - Readers rerouted through `runtime_env.getenv`: `output_shaper.py`, the anthropic holdout read, and the ast-grep threshold (now a live read, not an import-time constant). - Proxy: loopback-only `POST /admin/runtime-env` applies overrides in memory; `/health` → `config.runtime_env` surfaces the live values so reuse is observable. - `wrap`: after attaching to a proxy (all call sites), best-effort push of the session's **explicitly-set** knobs. No-ops if nothing is set, `--no-proxy`, the proxy is unreachable, or it predates the endpoint (404). Only explicitly-set knobs are pushed, so a session never clobbers another with a default it never asked for. - Docs: README + output-token-reduction guide document the global-override caveat. ## 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_runtime_env.py -q 16 passed $ python -m pytest tests/test_runtime_env.py tests/test_output_shaper.py -q 50 passed $ ruff check headroom/proxy/runtime_env.py headroom/proxy/output_shaper.py headroom/proxy/handlers/anthropic.py headroom/proxy/interceptors/astgrep.py headroom/proxy/server.py headroom/cli/wrap.py All checks passed! $ mypy headroom/proxy/runtime_env.py Success: no issues found in 1 source file ``` ## Real Behavior Proof - Environment: local macOS, Python 3.12 `.venv`, branch `fix/runtime-env-hot-reload` at the PR head. - Exact command / steps: ran the test suites above. The 16 new `test_runtime_env` tests exercise the registry/store, overrides reaching the shaper + the ast-grep threshold, the `POST /admin/runtime-env` apply + `/health` reflect + loopback-only 404 + 400-on-non-object, and the wrap push payload / no-op / error-swallow paths. - Observed result: 50 passed; ruff + mypy clean on the changed modules; an override set via the endpoint is read by `getenv()` at the shaper and surfaced in `/health` config. - Not tested: a literal two-terminal manual session (start a proxy, `headroom wrap` a second session, `export HEADROOM_OUTPUT_SHAPER=1`, confirm the reused proxy picks it up). The behaviour is covered by the endpoint + wrap-push integration tests, but was not exercised by hand here. ## 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 - [x] 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 ## Additional Notes - **Inherent caveat (documented):** overrides are global to the proxy — one process serves every attached wrapper, so the last explicit setting wins. No mechanism (restart or hot-reload) can give two sessions on one shared proxy different output-shaper settings. - **Scope:** startup-captured settings (`HEADROOM_TARGET_RATIO` etc.) are intentionally out of scope — a fresh proxy already gets them and they ride the existing `/health` config channel. - **Merge blocker:** this branch is currently **CONFLICTING with `main`** and needs a rebase/merge before it can land. - CHANGELOG.md left unchanged — releases are managed by release-please from conventional commits.	2026-06-18 09:50:50 -07:00