Tobias Koppers b145ad6f3f Fix initial Turbopack HMR update handling (#98385) ...

### What?

Prevent a real client HMR update from being discarded when it arrives as
the first subscription emission.

### Why?

Capturing the chunk baseline and installing the update subscription are
separate asynchronous operations. A change between them turns the first
emission into a real update, but the client handler previously assumed
that emission was always initialization-only and dropped it after the
server had advanced its version state.

### How?

Inspect the first subscription result and preserve the existing
issues-only initialization behavior while forwarding partial or restart
updates through the normal issue and browser-update paths. This is the
narrower option because it does not change handling of the usual initial
issues payload.

### Verification

- `pnpm --filter=next build`
- `HEADLESS=true pnpm test-dev-turbo
test/development/app-dir/hmr-dynamic-component/hmr-dynamic-component.test.ts`
(including a locally controlled baseline-to-subscription race)
- Prettier and ESLint on the changed source

<!-- NEXT_JS_LLM -->

<!-- fleet 3820fb8a-c662-4c74-8316-e2d7cd42bfbd -->

---------

Co-authored-by: vercel-fleet-prod[bot] <318278635+vercel-fleet-prod[bot]@users.noreply.github.com>
Co-authored-by: Tobias Koppers <1365881+sokra@users.noreply.github.com>

2026-09-09 08:07:34 -07:00

..

app

…

chunk-list-subscriptions.test.ts

…

hmr-dynamic-component.test.ts

Fix initial Turbopack HMR update handling (#98385)

2026-09-09 08:07:34 -07:00