Make TurbopackResult payloads disjoint (#98575)
### What?
Refactors the JavaScript-facing `TurbopackResult<T>` into a stable
wrapper whose payload lives under `value` and whose issues remain
top-level. Native API consumers, entrypoint conversion,
development-server paths, HMR handling, and direct API tests now follow
the disjoint shape.
Two event subscriptions that had inaccurate wrapper declarations now
expose their existing plain runtime payloads explicitly: update-info
events remain `UpdateMessage`, and compilation events remain
`CompilationEvent`. Nullable native entrypoint payloads are also
declared accurately and normalized at the JavaScript API boundary.
### Why?
The previous intersection-based representation merged payload fields
with result metadata. That allowed fields such as `issues` to overwrite
one another and caused non-object payloads to be discarded, making the
result shape depend on `T`. A dedicated payload property avoids those
collisions and preserves every payload type, including `null`.
Keeping plain event streams distinct from result wrappers also ensures
`TurbopackResult<T>` consistently means the native API actually provides
wrapper metadata.
### How?
The N-API serializer now always creates a fresh wrapper rather than
mutating an object payload. The shared TypeScript type models that
wrapper directly and requires an explicit payload type. Conversion
layers replace only the nested payload while explicitly preserving
wrapper issues. Call sites continue to process wrapper issues while
reading domain data through `value`.
The update-info and compilation-event declarations were aligned with
their native callback types instead of introducing new runtime wrappers
for streams that do not collect issues. Rust `Option<NapiEntrypoints>`
payloads are declared as nullable, then normalized to the existing
empty-entrypoints representation after a null-safe route check.
### Verification
- `pnpm build-all`
- `pnpm --filter=next types`
- `pnpm swc-build-native`
- `cargo check -p next-napi-bindings`
- `cargo fmt --all -- --check`
- ESLint and Prettier on changed files
- `pnpm test-dev-experimental-turbo
test/development/app-aspath/app-aspath.test.ts`
- `pnpm test-dev-turbo test/development/basic/next-rs-api.test.ts` — 26
passed, 1 skipped, 15 snapshots; Jest reported lingering open handles
after the green summary
- `pnpm test-dev-turbo
test/development/app-dir/concurrent-install/concurrent-install.test.ts`
- `pnpm test-dev-experimental-turbo
test/development/app-dir/concurrent-install/concurrent-install.test.ts`
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Co-authored-by: vercel-fleet-prod[bot] <318278635+vercel-fleet-prod[bot]@users.noreply.github.com>
Co-authored-by: Will Binns-Smith <755844+wbinnssmith@users.noreply.github.com>
