unplugin under Vite: environments built in parallel share one pipeline

[codecaaron]

Release fix (released by reading; loud and opt-in): unplugin's Vite adapter failed any custom buildApp that builds environments in parallel. Found by the teardown follow-up probe after #395.

The bug

Each environment's buildStart made a new ExtractionSession for the same build (runClaimedPipeline), and the second collided with the first's claim: [animus] "animus-unplugin:…" started an analysis of build …, which "animus-unplugin:…" publishes. Unlike vite-plugin before #395, it failed at once, not only when one environment was slow. v0.1.25 had the same shape (a new Session per buildStart, closed in buildEnd, a process-global claim). Vite's default buildApp is sequential, so only a custom parallel one hits it.

Fix

Under Vite, Rollup and Rolldown the plugin tracks open environment builds by name:

• a buildStart while another environment's build is open joins the running pipeline (joinPipeline) instead of claiming again;
• buildEnd emits its assets, and disposes the session directory and releases the claim only when the last environment ends;
• a build of an environment whose build is open (a reused builder, or a second environment under one name) waits for that build's end, then opens its own generation; buildEnd (once per build) ends only the generation its environment opened (last round, 51a9c07, replacing the refusal, which let a refused build's end dispose the shared session directory under the original build).

webpack-like hosts run one compile at a time and are not tracked (#397 covers their restarts).

Witness

unplugin/tests/vite-parallel-build.test.ts › both environments build from one shared analysis: a real Vite 8.2.2 createBuilder over vite-plugin's dev fixture with animusUnplugin.vite, client and SSR in parallel; SSR output must be extracted. Red on main a5d1f49 with the claim error.

Last-round witness

a builder reused while an earlier build still runs keeps that build its assets (f799c47): badge.svg through an asset() image scale read by a Badge background, SSR emitting assets, the builder reused while the slow original SSR build still runs; all four builds settle, the original SSR fulfils and its output carries the badge SVG. Red at c449922.

Checks

macOS at f799c47: unplugin 34/34, lint and fmt clean. Linux CI: run 38176081147 (c449922) and run 38177499710 (f799c47), every job green.

🤖 Generated with Claude Code

[codecaaron]

Parked by root under the stopping rule after the final round. spike-codex confirmed the reused-builder findings closed (all four builds settle correctly; the original SSR keeps its assets), but the serialise shape introduces a circular wait: a plugin whose transform awaits a nested build of the same environment hangs, because the nested buildStart awaits the outer build's buildEnd (vite-plugin context.ts:517-521 / unplugin core.ts:529-537). The earlier refusal heads fail that case loudly instead. Owner decision pending: ship this head with the nested-build case as a stated limit, ship the refusal head, or leave parallel buildApp unsupported (main fails it loudly).

🤖 Generated with Claude Code