Lower fetch members typed by @types/node, and run the poll phase once per loop iteration

[cramforce]

Stacked on #1425.

Summary

Fetch-family members under @types/node. undici-types, which supplies @types/node's fetch declarations, declares the Headers methods and the Request/Response body mixin as function-typed properties (readonly append: (name: string, value: string) => void). scriptc's own declarations use methods.

The receiver-call lowering took a property-declared member to be a stored callback. Under @types/node:

• Headers.forEach was refused at build time.
• append, get, set, delete, has and getSetCookie built, then threw … is not a function at run time.

A member whose declarations all come from the standard library now takes the shared receiver dispatch, whichever declaration file supplies its type.

The rest of the fetch family behaves the same with either set of declarations: Response status, headers and body methods, Response.json, Request reads, and AbortController. Iterating a Headers (keys, values, entries, for-of) stays refused under both.

Poll phase ordering. The event loop restarts its turn whenever a callback queues microtasks, and every restart drained the net poller again. So I/O that became ready during the iteration's own callbacks, such as a loopback connect started by a 'data' handler, ran before the check phase. Immediates queued earlier then ran after it. Node delivers that I/O in the next iteration's poll phase.

The net unit now drains its poller once per loop iteration. A full batch keeps draining. The poller reopens after the check phase has run, or when no immediates are pending. Deferred emits still run on every call.

The visible effect: back-to-back await request() calls on an undici Agent now open the same number of connections as Node (2, not 3), so the undici fixtures no longer need a setImmediate turn between requests.

Evidence

• tests/fixtures/node-types/fetch-handle-members.ts: Headers, Request and Response members typed by undici-types, run against Node through project-config.test.ts.
• Corpus 6251-net-connect-poll-phase-order: the order of a new connection's 'connect' against nextTick, promise jobs and setImmediate, directly and through awaited promises. It fails with the previous runtime and matches Node with this one.
• The undici5/undici7 npm cases drop the setImmediate workaround and still match Node, plain and sanitized.
• Event-loop, server, fetch, dgram, portless and native-proxy suites, plus the differential corpus filtered to I/O, timers, streams and promises: the failure set is identical with and without the runtime change, apart from 6251, which only the old runtime fails. Every remaining failure is environmental (the sandbox runs Node 24.15; main pins 24.22). The sanitized lane shows the same.
• Zero-cost gate against Compile undici from a built-in implementation #1425: IR and LLVM are identical for every program. Executables that link the event loop differ only in scr_loop_run and the new scr_loop_io_open (+40–128 B), which is the intended runtime change.
• Runtime benchmarks against Compile undici from a built-in implementation #1425 (4 layouts × 16 runs): async-pipeline 9.88 → 9.97 ms, cli-config 1.68 → 1.69 ms, http-api 490.8 → 488.1 ms, server throughput 81.5k → 81.9k req/s. Geomean +0.3%, within noise. Self-compile −0.6%.
• Lint, format, test:ts7 --baselines-only (2 new baselines), and the self-host IR build (exit 0, no diagnostics).

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Project	Deployment	Actions	Updated
scriptc	Ready	Preview, v0	Oct 20, 2026 3:51pm UTC

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Additional findings

1. packages/compiler/shims/undici/core/fetch.ts:517-523 — When a redirect response has an unfinished body, removing its abort listener without cancelling the request leaves its connection occupied even after fetch finishes or the caller aborts.