Struct Engine 

pub struct Engine<'a> { /* private fields */ }

The §8 engine: an anvil, a plugin chain, and the op’s Log sink. It emits the op-level lifecycle records (begin/seal/abort, §6), interleaved with the per-plugin invoke/envelope records the Plugins seam writes there.

Implementations

impl Engine<'_>

pub fn diffless( &self, op: Verb, checkout: &Path, pre: &[PluginRef], post: &[PluginRef], ) -> Result<(), OpError>

Run a DIFFLESS op (§8 “skip steps 1/3/5”): pre/post against the checkout (the STORE for sync, §13), no worktree, no seal. Tier 1 is empty, so the unwind is reverse plugin rollback only (§13/§14). Unlike the seal path there is no commit to land, but the op can still MOVE the anvil tip — a pre participant (sync ff) advances tasks_branch. So balls reads the tip before pre and after it and threads those as the §13 previous_commit/commit facts to post (and any post-phase rollback), metadata-less: a diffless op authors no §5 message, so message is None and the wire omits metadata. No shipped plugin reads them yet; a sync/post cache-rebuild participant will.

pub fn prime( &self, pre_dir: &Path, post_dir: &Path, pre: &[PluginRef], post: &[PluginRef], step: &mut dyn FnMut() -> Result<Option<String>>, ) -> Result<(), OpError>

Run prime’s split-checkout pass (§12, bl-698d): pre ONCE against pre_dir (the LANDING — the store may not be materialized yet), then step, core’s between-phase work: materialize the store for the configured tasks_branch and report the dial — None ⇒ it held, Some carries the value that moved. A moved dial ABORTS: no conformant plugin rewrites tasks_branch in prime/pre (config crosses only by install, §12/§13), so the check ENFORCES the consent rule — fail, not silent — the error naming the rule and the moved value. When the dial held, post runs against post_dir (the materialized store — the tracker’s fetch-ff + push). step’s failure is an OpError::Substrate abort; any abort unwinds the run plugins in reverse (no seal, no §7 facts — prime’s push reads neither). A PLUGIN abort is rendered as the §12 catalog’s E7 — “plugin failed during prime, rolled back K prior” (K = the plugins that had run and were unwound) — not the generic abort (bl-3ddb). The whole op logs one begin/done/abort.

impl<'a> Engine<'a>

pub fn new(anvil: &'a dyn Anvil, plugins: &'a dyn Plugins, log: &'a Log) -> Self

Build an engine over an anvil, a plugin chain, and the op’s log sink.

pub fn seal( &self, base: &dyn BaseChange, op: Verb, change_dir: &Path, pre: &[PluginRef], post: &[PluginRef], ) -> Result<String, OpError>

Run a MUTATING op (§8 steps 1–6): Author → Pre → Seal → Post → Teardown, with §14 rollback on any abort. pre/post are the committed [hooks] plugin sets resolved at op-start (§6). Logs begin/seal/abort (§6); returns the sha.