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## Description
Adds a Rust-only `headroom-simulators` workspace crate: a deterministic
local upstream simulator service for Headroom proxy and pipeline
validation. It supplies configurable stubs plus bottled provider-shaped
responses for supported provider/path surfaces without calling real
LLMs.
## 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
- Added `crates/headroom-simulators` Rust crate with library and
`headroom-simulators` binary.
- Added clean domain classification for supported surfaces: Anthropic
`/v1/messages`, OpenAI chat/responses/conversations, Bedrock
invoke/stream routes, Vertex raw/stream predict, health, and generic
fallback.
- Added JSON-configured stub matching by method, path, body substring,
and JSON pointer.
- Added bottled provider-shaped JSON, SSE, and Bedrock EventStream
responses for unconfigured requests.
- Added a container `Dockerfile` and README for local/GitHub Actions
usage.
- Added unit and HTTP integration tests for defaults, configured stubs,
SSE, Vertex, and Bedrock EventStream behavior.
- Added proxy-level simulator-backed E2E tests that run Headroom against
the simulator across Anthropic, OpenAI Chat, OpenAI Responses, OpenAI
Conversations, Bedrock invoke/converse/streaming, Vertex raw/stream
predict, and upstream health.
- Added simulator-backed provider error-path E2E coverage for OpenAI
429, Anthropic 529, Bedrock 502, and Vertex 503 responses flowing
through Headroom unchanged.
- Added Headroom-owned preflight error E2E coverage proving Bedrock
missing credentials and invalid Vertex envelopes stop inside the proxy
instead of silently falling through to the simulator/provider.
- Fixed direct Rust `headroom-core` binaries/tests on Windows so Magika
initializes ONNX Runtime via `ort::init_from` from an explicit pip
`onnxruntime` library path, with fail-fast fallback only when no safe
runtime is discoverable.
- Added a Rust CI `simulator-e2e` matrix for `ubuntu-latest`,
`macos-latest`, and `windows-latest` that runs `cargo test -p
headroom-proxy --test e2e_simulators`.
- Gated dynamic Magika `Path`/`PathBuf` imports to Windows and x86_64
macOS so Linux clippy does not see unused dynamic-ORT-only imports.
## Testing
- [ ] Unit tests pass (`pytest`)
- [ ] Linting passes (`ruff check .`)
- [ ] Type checking passes (`mypy headroom`)
- [x] New tests added for new functionality
- [x] Manual testing performed
### Test Output
cargo fmt --all -- --check
# passed
cargo clippy --workspace -- -D warnings
# passed
$env:ORT_DYLIB_PATH=$null
cargo test -p headroom-core transforms::magika_detector::tests:: --lib
# 17 passed, 0 failed; Magika initialized from discovered pip
onnxruntime DLL
$env:ORT_DYLIB_PATH=$null
cargo test --workspace
# passed
gitleaks protect --staged --no-banner --redact
# no leaks found
gitleaks git --log-opts="headroomlabs/main..HEAD" --no-banner --redact
# 5 commits scanned; no leaks found
## Real Behavior Proof
- **Environment:** Windows PowerShell, Rust toolchain `1.95.0`, clean
worktree from `headroomlabs/main` at `
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|---|---|---|
| .. | ||
| src | ||
| tests | ||
| Cargo.toml | ||
| Dockerfile | ||
| README.md | ||
Headroom Simulators
headroom-simulators is a local, deterministic upstream for Headroom proxy tests.
It serves provider-shaped responses without contacting real LLM APIs.
cargo run -p headroom-simulators -- --listen 127.0.0.1:8789
Optional JSON config:
{
"stubs": [
{
"name": "exact chat smoke",
"method": "POST",
"path": "/v1/chat/completions",
"body_contains": "ping",
"response": {
"status": 200,
"headers": {"x-simulator": "configured"},
"json": {"ok": true}
}
}
]
}
Point the proxy at http://127.0.0.1:8789 to run local or CI validations.