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/.

Everything is in this repo, Apache-2.0, and builds offline from source. No part of the engine is fetched at build time.

Layout

Cargo.toml              the workspace (crates/*), release profile
rust-toolchain.toml     the channel plus the wasm32 target
ENGINE_VERSION          which engine release the launcher / npm shim download
.cargo/config.toml      the `cargo xtask` alias
browser-bundle/         the page JS the in-page bundle is built from
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   JS-semantics helpers, color, findings, the rule registry, inline
               ignores, the Dom trait, SnapshotDom, and the plain-data types
               every check takes in and hands back
  core         the rule logic: every `check_*` / `scan_*` and its heuristics,
               the browser rule adapters, the visual-contrast decisions
  wasm         wasm-bindgen exports over `core` (the in-page bundle and the
               extension's offscreen core)
  xtask        `cargo xtask bundle`: builds the in-page bundle and the
               extension pieces

crates/core re-exports the foundation modules under its own paths, so every consumer names one crate: impeccable_core::js, impeccable_core::color, impeccable_core::checks::rules::check_colors, impeccable_core::browser::driver::collect_browser_findings. The split between the two crates is about what a check is written against, not about who may see it.

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, then 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), then target/release/impeccable, so a plain cargo build --release -p impeccable is enough.

The frozen function-level vectors in tests/oracle/vectors/calls/ replay through impeccable_core::vectors::call (cargo test -p impeccable-core), which is the union of foundation's dispatch arms and the core's.

The browser bundle

The same rules that run natively run in a page, compiled to WebAssembly. cargo xtask bundle is the one command that produces every browser artifact:

1. wasm-pack build crates/wasm --target no-modules --release into target/wasm-bundle/ (opt-level z, then wasm-opt).
2. Concatenate the page JS in browser-bundle/*.js in a fixed order with the wasm-bindgen glue and the .wasm embedded as base64. The page JS only implements the Dom probe, marshals JSON, and draws the overlay; no rule logic lives there.
3. Write dist/detect-antipatterns-browser.js and dist/antipatterns.json, and copy the bundle to crates/live/assets/detect-antipatterns-browser.js. That copy is a tracked generated file: crates/live/src/browser_assets.rs embeds it with include_str! and the live server hands it to the browser as /detect.js, so the binary has to carry it.
4. Write the five extension pieces into extension/detector/ (snapshot.js, overlay.js, core.js, core_bg.wasm, antipatterns.json). That directory is gitignored; bun run build:extension runs this task and then packages the zips.

cargo xtask bundle --check rebuilds and fails when the tracked live asset is stale, which is the CI staleness gate. The build is deterministic: same sources, same bytes.

wasm-pack is the one extra tool this needs (cargo install wasm-pack --locked) plus the wasm32-unknown-unknown target, which rust-toolchain.toml requests. IMPECCABLE_XTASK_SKIP_WASM_PACK=1 reuses whatever is already in target/wasm-bundle/, for iterating on the page JS alone. IMPECCABLE_EXTENSION_SKIP_BUNDLE=1 lets bun run build:extension skip the bundle step when extension/detector/ is already complete, for CI matrices that pre-built it.

Run cargo xtask bundle after touching crates/core, crates/wasm, or browser-bundle/, and commit the refreshed live asset.

Rule packs

The built-in rules are compiled in and always run. A rule pack is how a crate that depends on this workspace adds rules of its own without forking it: one process-lifetime value carrying its own registry rows plus the hooks it has rules for. With no pack installed nothing changes, which the oracle enforces byte-for-byte.

The traits:

• impeccable_core::rule_pack::RulePack (object-safe, Send + Sync + Debug) with three hooks, each defaulting to empty: check_text(content, file_path, ext) for the text engine, check_element_dom(dom, el) and check_page_dom(dom) for the browser engines.
• impeccable_html::StaticRulePack with check_document(doc, file_path). The StaticDocument model belongs to crates/html, and detect cannot name a type from a crate that depends on it, so the static engine's hook is a separate trait. A pack that covers HTML implements both.

Three steps for the downstream crate: declare static ROWS: &[Antipattern] with namespaced ids (mypack/my-rule) and return them from registry(); call impeccable_core::rule_pack::install(&PACK) once at startup, which is what makes get_antipattern resolve the pack's ids and therefore what gives its findings a name, description, category, and severity; then pass the pack to the engine being run.

Where a pack reference travels:

Engine	Field
text	TextOptions.rule_pack, ScanOptions.rule_pack
static HTML	DetectHtmlOptions.static_rule_pack and .rule_pack; StaticHtmlEngine.static_rule_pack for the Engines seam
browser / snapshot	BrowserConfig.rule_pack (#[serde(skip)]: a pack is a Rust value, never JSON from the page)

Where each hook runs, and why there:

• Text engine (detect_text): after every built-in matcher, style-block and CSS-in-JS pass, the design-system scan, the dedupe, and the page analyzers, and before inline ignores. Appending last keeps built-in output identical, and being inside the waiver step means impeccable-disable covers a pack's rules the same way it covers built-in ones.
• Static HTML engine (detect_html_source): after the element rules, the design-system merge, the page-level checks and the pattern checks, again just before inline ignores. An HTML file gets exactly one pack pass: static_rule_pack when it is set, otherwise rule_pack.check_text over the raw HTML source, which is how a text-only pack still covers .html files. A pack that implements both never reports the same file twice.
• Browser driver (collect_browser_findings): check_element_dom runs at the end of the driver's per-element loop, through the same disabled-rules filter and grouped onto the same element as the built-in findings; check_page_dom runs after every built-in page pass, attributed like the built-in checks that name their own element (el: None means document.body). skipScan skips the pack too.

The registry keeps ANTIPATTERNS as the built-in list and consults the registered rows after it (registry::extend, registry::all_antipatterns). extend is idempotent per slice and panics on an id collision, so a pack can never shadow a built-in rule. Registration is append-only and has no undo: a pack is a property of the process, not of a run.

The wasm detect feature

crates/wasm builds with --features detect for hosts that cannot exec the binary (Cloudflare Workers and other wasm sandboxes). It adds two exports over the file-scanning engines, JSON in and JSON out:

• detect_text_json(content, file_path, options_json)
• detect_html_source_json(html, file_path, options_json)

Both take { inlineIgnores?: boolean, designSystem?: { frontmatter?, sidecar? } } and return the findings array impeccable detect --json prints, same keys and same order. designSystem carries the DESIGN.md inputs rather than a normalized object, because the JS API's normalized form used Sets and Maps that JSON cannot hold. Unparseable options fall back to the defaults. antipatterns_json() lists the built-ins followed by any pack's rows.

A pack reaches those exports through impeccable_wasm::set_rule_pack and exports_detect::set_static_rule_pack, both Rust-only: the consumer is a crate that links impeccable-wasm as an rlib, registers its pack, and runs wasm-pack over itself. There is deliberately no JS-facing setter.

cargo build -p impeccable-wasm --features detect --target wasm32-unknown-unknown --release

Pristine (the PR design-review bot) is the first consumer: its rules/ crate carries pristine/* rules on all three hooks and reaches the engine through this feature, replacing the detectText call it makes into the npm impeccable@3 package today.

Releases

Two release kinds touch the runtime, in this order:

1. Engine (engine-v<ENGINE_VERSION>): bun run release:engine verifies the version, the npm platform-package pins and a clean tree, then 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>/.
2. npm platform packages, then the skill and CLI releases, which scripts/check-engine-release.mjs gates on the engine release.

The extension ships its own vendored WASM core and never execs the engine binary, so bun run release:ext is exempt from that gate. It does need bun run build:extension (and therefore a Rust toolchain and wasm-pack) before the zip is attached.

CI runs the workspace build and tests (rust, rust-windows) and replays the oracle against a release build from the checkout under test.