headroom/docs
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
..
app docs: improve discoverability for AI agents and search crawlers 2026-05-13 17:36:06 -07:00
components tokens saved grid 2026-04-12 13:42:20 +06:00
content/docs feat(vertex): turnkey Claude Code + Vertex compression (+ fixes from the Vertex review) (#1113) 2026-06-18 00:56:23 -07:00
lib docs(ci): add CI/CD flow diagrams (#1062) 2026-06-16 23:05:15 -07:00
overrides fix: repair release and docs pipelines 2026-04-16 12:53:51 -05:00
proposals feat(vertex): turnkey Claude Code + Vertex compression (+ fixes from the Vertex review) (#1113) 2026-06-18 00:56:23 -07:00
screenshots Merge pull request #147 from JerrettDavis/feat/anthropic-usage-insights 2026-04-12 10:54:22 -07:00
spec docs: align MCP proxy docs with implemented API (#614) 2026-06-10 21:14:23 -05:00
.gitignore new docs UI + ts doc coverage 2026-04-12 13:15:58 +06:00
auth-modes.md fix: PR-F1 classify_auth_mode helper (Phase F kickoff) 2026-05-03 17:20:14 -07:00
bedrock.md feat(bedrock): cross-region + Converse compression; bundle proxy binary in images (#999) 2026-06-16 09:45:24 -05:00
bun.lock fix(docs): update bun.lock to next 16.2.6 for GHSA-h64f-5h5j-jqjh (CVE-2026-44577) 2026-06-02 04:25:21 +00:00
next.config.mjs new docs UI + ts doc coverage 2026-04-12 13:15:58 +06:00
observability.md fix(observability): G3 remediation — bound cardinality + wire dead metrics 2026-05-24 10:41:56 -07:00
output-token-reduction-guide.md feat(proxy): hot-reload live env knobs so a reused proxy picks them up without a restart (#1090) 2026-06-18 09:50:50 -07:00
package-lock.json ci: bump the npm_and_yarn group across 3 directories with 3 updates (#1056) 2026-06-16 23:07:34 -07:00
package.json ci: bump the npm_and_yarn group across 3 directories with 3 updates (#1056) 2026-06-16 23:07:34 -07:00
postcss.config.mjs new docs UI + ts doc coverage 2026-04-12 13:15:58 +06:00
proxy.ts new docs UI + ts doc coverage 2026-04-12 13:15:58 +06:00
README.md new docs UI + ts doc coverage 2026-04-12 13:15:58 +06:00
rtk-architecture.md fix(observability): wire Phase G PR-G3 RTK + proxy metrics (H-blocker) 2026-05-22 13:18:42 -07:00
source.config.ts docs(ci): add CI/CD flow diagrams (#1062) 2026-06-16 23:05:15 -07:00
tsconfig.json new docs UI + ts doc coverage 2026-04-12 13:15:58 +06:00

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