Module build 

PM.5: the build service — a plugin source directory becomes a cached .wasm component.

Design: plugin-manager.md §5. One primitive with two callers (§6): every user plugin, and the user’s own init.rs.

The requirement that shapes everything here

A warm boot with an unchanged source must not rebuild. A cold component build is seconds to minutes; paying that on every start would make the editor unusable, so the service is a cache with a build fallback, not a build step with a cache in front. That is what the .build-stamp is for: it records what the artifact was built from and (WT.3) what it was built against, and a stamp matching on both short-circuits to a pure load.

The second half is not symmetry for its own sake. A source that did not change, compiled against an ABI that did, looked current under a source-only stamp — so it was loaded, failed to instantiate, and said nothing at all. That is the whole of the failure wit-ownership.md was written for, and no amount of source fingerprinting can see it.

Failure is a skip, never a stall

Three failure modes, three different answers, and the middle one is the one worth naming:

• No artifact, build fails → BuildOutcome::Failed. The plugin does not load. Logged, surfaced in :plugins; boot continues.
• An artifact exists, a stale rebuild fails → BuildOutcome::StaleKept. The previous artifact keeps loading. A user who pushes a broken revision to a plugin they depend on should lose the new code, not the working editor they had five minutes ago.
• Stamp matches → BuildOutcome::Cached. No toolchain is invoked at all, so a machine with no Rust installed still boots every already-built plugin.

Nothing in this module panics and nothing blocks: the caller runs build_plugin on spawn_blocking (paramount goal #1 / #4 — never the boot or actor thread).

Structs

CargoComponentBuilder

The real builder: cargo build --release --target wasm32-wasip2.

Stamp

WT.3: what a cached artifact was built from and against.

Enums

BuildOutcome

What build_plugin did.

Traits

ComponentBuilder

Produces a .wasm component from a source directory.

Functions

artifact_path

Where a plugin’s cached artifact lives.

build_plugin

Build name from source_dir into user_root, unless the cached artifact is already current.

source_stamp

A fingerprint of source_dir’s contents, for staleness comparison.