pbakaus_impeccable/docs/ENGINE.md

The engine: the Rust runtime behind every skill verb

Every command the skill text runs is {{scripts_path}}/impeccable <verb>. The launcher next to the skill (skill/scripts/impeccable, impeccable.cmd) finds or downloads one static binary per platform and execs it. That binary is built from this repo's Cargo workspace. There is no Node at runtime.

This page is the map for anyone building or changing the runtime. The observable behavior of every verb is specified in CLI-CONTRACT.md and pinned byte-for-byte by tests/oracle/.

Layout

Cargo.toml              the workspace (crates/*), release profile
rust-toolchain.toml     EXACT rustc pin (see "The closed detector")
DETECTOR_VERSION        which prebuilt detector release crates/core links
ENGINE_VERSION          which engine release the launcher / npm shim download
crates/
  cli          the `impeccable` binary: verb router, exit codes
  common       Io handle (stdout/stderr/stdin/env/cwd), path + process helpers
  context      context, doctor, staleness, signals, concept-seed, pin, ...
  hook         the design hook (hook, hook-before-edit, hook-admin)
  live         live mode: server, wrap, accept, manual edits, Svelte/Vue
  skills       install / update / check / link (the old npm CLI verbs)
  comp         comp-fidelity pure libs (raster, png, metrics, fonts)
  comp-verbs   build-phase, comp-diff, comp-spec, font-match
  detect       `impeccable detect`: file walk, config, ignores, output, regex engine
  html         the static HTML engine: parser, cascade, static DOM, rule adapters
  browser      the URL engine: Chrome discovery, CDP, snapshot, visual pass
  foundation   OPEN helpers + boundary types: JS-semantics helpers, color,
               findings, registry, inline ignores, the Dom trait, SnapshotDom
  core         the shim: re-exports foundation under the paths every crate
               uses, and forwards the rule checks to the closed detector

Build and test:

cargo build --release -p impeccable      # target/release/impeccable
cargo test --workspace
IMPECCABLE_BIN=target/release/impeccable node tests/oracle/run.mjs   # the behavior gate

bun run test and the oracle find the binary through IMPECCABLE_BIN or skill/scripts/bin/<os>-<arch>/ (bun run fetch:engine downloads the pinned release there; IMPECCABLE_BIN=target/release/impeccable bun run fetch:engine copies a local build).

The closed detector

The rule engine itself (the checks, the browser rule adapters, the visual contrast decisions) is proprietary and lives in a private repo. It ships as a prebuilt native archive per target, libimpeccable_detector-<os>-<arch>.a (impeccable_detector-windows-x64.lib), published as the GitHub Release detector-v<DETECTOR_VERSION> on this repo, next to detector-browser-bundle.zip (the same rules compiled to wasm for the extension, the live overlay and the site).

crates/core/build.rs resolves the archive in this order and links it:

1. IMPECCABLE_DETECTOR_LIB=<dir>: a directory holding the archive for the current target (a local build of the detector repo).
2. ~/.impeccable/detector/<DETECTOR_VERSION>/<os>-<arch>/ (IMPECCABLE_HOME moves the root).
3. A download from detector-v<DETECTOR_VERSION> into that cache, verified against the .sha256 sidecar. IMPECCABLE_DETECTOR_BASE overrides the release root; IMPECCABLE_DETECTOR_OFFLINE=1 refuses to download.

Three things follow from how that archive is made, and they are the reason for three otherwise odd-looking settings:

• The toolchain is pinned to an exact version. The archive is the closed crates' rlib objects repacked with llvm-ar, with no std inside. Its objects reference std by mangled symbol name, which only resolves against the same rustc build. rust-toolchain.toml pins it; rustup installs it on first cargo invocation. A toolchain bump needs a new detector release.
• The release profile has lto = false. Fat and thin LTO internalize std symbols the opaque archive still needs and the link fails with "symbol(s) not found". Cargo's default thin-local LTO stays.
• crates/core keeps the old paths. Nothing outside crates/core and crates/foundation knows about the boundary: impeccable_core::checks:: rules::check_colors is a one-line shim that encodes its argument, calls the archive, decodes the result. The C-ABI is three symbols (det_abi_version, det_call, det_free) and a host vtable the closed side uses to call back into the open Dom / StyleMap implementations. Every id and every type that crosses is declared in crates/foundation/src/boundary.rs; the shim checks the ABI number once and panics with a clear message when the archive was built for another.

The frozen function-level vectors in tests/oracle/vectors/calls/ replay through the shipped archive (impeccable_core::vectors::call forwards unknown names to it), so the black box is verified the same way the open code is.

Releases

Three release kinds touch the runtime, in this order:

1. Detector (detector-v<X>, published by the private repo's CI to this repo's Releases). DETECTOR_VERSION here pins it.
2. Engine (engine-v<ENGINE_VERSION>): bun run release:engine verifies the detector release exists (scripts/check-detector-release.mjs), tags, and pushes; .github/workflows/release-engine.yml builds the five targets and publishes the binaries with .sha256 sidecars. The launcher, the npm shim and impeccable install download from github.com/pbakaus/impeccable/releases/download/engine-v<X>/.
3. npm platform packages, then the skill and CLI releases, which scripts/check-engine-release.mjs gates on the engine release.

CI runs the workspace build and tests (rust, rust-windows) and the oracle against a source build; both are warn-only until the first detector release exists, then their continue-on-error flips to false.

Working on the detector

Changes to rule logic happen in the private detector repo. Point the shim at a local build while iterating:

# in the detector repo
cargo xtask detector-archive --out /tmp/det
# here
IMPECCABLE_DETECTOR_LIB=/tmp/det cargo test --workspace

Adding a function that the open crates call: add its id to foundation/src/boundary.rs (never renumber), the shim in crates/core, the dispatcher arm in the detector repo, and bump boundary::ABI if any existing signature or type changed. The shim's test diffs the two id tables.