fix(ext/http): keep request body readable after response is sent - #36629

)

Fixes #36624

Deno 2.8.3 through 2.9.5 stopped delivering request body chunks to a
Deno.serve handler once it started writing a streaming response, so the
deno-fetch event stream echo tests deliberately asserted the stall. Deno 2.9.6
fixed it (denoland/deno#36629), which made those assertions fail in CI.

Both Deno adapters are full-duplex now, so the FULL_DUPLEX_ADAPTERS gate and
its stall branches are removed.

…pnpm (#82)

Bun 1.4 and Deno 2.9.6 both fixed stream behavior that the Bun and Deno
test suites deliberately asserted as broken, so CI on main has been red
since Bun 1.4.0 landed and the Deno failures surfaced right after. The
failures are runtime behavior changes, not standardserver bugs, and the
tests now assert the fixed behavior instead of skipping anything.
Alongside that, `@types/node` and `@types/bun` are bumped,
`EventStreamDecoderStream` no longer declares `implements
ReadableWritablePair`, pnpm is now declared through `devEngines` so it
self-provisions, and Node 20 is dropped from the CI matrix.

## Bun 1.4: stream cancellation now propagates

Pure-Bun repros with no standardserver code show the same change between
Bun 1.3.14 and 1.4.0:

- Cancelling a response body now closes the connection, so the server
signal aborts and the stream cancel fires.
- A streaming request body is now cancelled on the client once the
server has responded, with or without keep-alive.
- An errored server response stream now reaches the client as an
`ECONNRESET` error instead of a clean end of body.

Both Bun adapters propagate request and response cancellation, so the
`REQUEST_STREAM_CANCEL_ADAPTERS` and `RESPONSE_STREAM_CANCEL_ADAPTERS`
gates and their else-branches are gone. One difference remains behind a
new `RESPONSE_STREAM_ERROR_ABORT_ADAPTERS` set: `Bun.serve` only aborts
`request.signal` when the client goes away, not when the server itself
closes the connection after its response stream errors. The test asserts
that current behavior so a future Bun change surfaces as a failure, same
convention as before.

## Deno 2.9.6: request body stays readable while streaming a response

Deno 2.8.3 through 2.9.5 stopped delivering request body chunks to a
`Deno.serve` handler once it started writing a streaming response, so
the `deno-fetch` event stream echo tests asserted the stall. Deno 2.9.6
fixed it (denoland/deno#36629), and CI picks up the latest Deno 2, so
those assertions started failing. Both Deno adapters are full-duplex
now, so the `FULL_DUPLEX_ADAPTERS` gate and its stall branches are
removed, with the minimum Deno version noted in the test.

## Types

- `@types/node` 26.1 → 26.4.1 across the workspace, `@types/bun` 1.3 →
1.4.0 for the Bun tests.
- `EventStreamDecoderStream` drops `implements ReadableWritablePair`.
Node's types only expose that name under `stream/web`, not as a global,
so the clause failed to resolve for consumers type-checking against Node
types alone. The class still exposes the same `readable`/`writable` pair
structurally, so nothing changes at runtime or for callers.

## Toolchain and CI

- pnpm is declared via `devEngines.packageManager` (`^11.0.0`, `onFail:
download`) instead of a `packageManager` pin, so any pnpm on a
contributor's machine or in CI provisions a compatible 11.x
automatically. The lockfile records the resolved 11.25.0 and picks up
refreshed resolutions within the existing dependency ranges.
- Node 20 is removed from the CI matrix. pnpm 11 requires Node 22.13+
and crashed on `node:sqlite` before running a single test on Node 20,
and Node 20 reached end-of-life in April 2026. The matrix is now 22, 24
and 26.

## Testing

- CI is green on Node 22, 24 and 26 at the current head: lint and
typecheck, tests with coverage, publish preview, benchmarks and codecov.
- Full `pnpm -w test` passes locally on the refreshed lockfile with pnpm
11.25.0: Bun 50 pass, Deno 4 suites / 50 steps pass, vitest 1076 tests
across 59 files pass.
- `bun test` on Bun 1.4.1 and `deno test` on Deno 2.9.6 each pass 3 of 3
repeated runs.
- `pnpm run type:check` passes for all 11 workspace projects with the
new types.
- Bun older than 1.4.0 or Deno older than 2.9.6 will now fail these
tests, matching the CI baseline (`pnpm runtime set bun 1` / `deno 2`).