node:http fails to link from a cold auto-optimize cache: js_bun_http_response_snapshot_json is web-fetch-gated but referenced unconditionally

[proggeramlug]

Summary

A cold auto-optimize link of any program importing node:http fails with an undefined symbol. Found while validating an unrelated PR; reproduces independently of it, and the causal chain is visible in the source on main.

Undefined symbols for architecture arm64:
  "_js_bun_http_response_snapshot_json", referenced from:
      perry_ext_http::server::bun_server::settle_value in
      libperry_ext_http.a(...perry_ext_http...cgu.10.rcgu.o)
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1
Error: Linking failed

Repro

// http_server.ts
import http from "node:http";
const server = http.createServer((req, res) => { res.end("{}"); });
server.listen(0, () => { console.log("listening"); server.close(); });

perry compile http_server.ts -o http_server from a cold cache (fresh
node_modules/.cache/perry, no warm target/perry-auto-*). A warm cache built
before this masks it, which is part of why it is not visible day to day.

Cause

js_bun_http_response_snapshot_json is defined in
crates/perry-stdlib/src/fetch/bun_server_bridge.rs:79. mod bun_server_bridge
is ungated, but its parent is not — crates/perry-stdlib/src/lib.rs:136:

#[cfg(feature = "web-fetch")]
pub mod fetch;

The auto-optimize rebuild for a node:http program selects

async-runtime, external-http-client-pump, external-http-server-pump,
external-net-tls, external-tls-server, external-ws-pump

which does not include web-fetch, so the whole fetch module — and the
symbol — is compiled out. Meanwhile perry-ext-http's
server/bun_server.rs declares and calls it unconditionally (3 references on
main). Definition and reference disagree about the feature that gates them.

Why CI is green

This is the CI-invisible class recorded in changelog.d/memory around #5112:
plain cargo build / cargo test never link the auto-optimize ext-http path,
so nothing in the normal suites exercises it, and any pre-existing warm
target/perry-auto-* cache hides it from a manual check too. Only a fresh
cold auto-opt link surfaces it.

Fix shapes

1. Gate perry-ext-http's use of the bridge on the same feature that gates its
   definition, so the two cannot disagree.
2. Have the driver add web-fetch whenever it selects the http server features
   (widens the build).
3. Move js_bun_http_response_snapshot_json out of the web-fetch-gated module
   into one that is always compiled when external-http-server-pump is on.

(1) or (3) look right; (2) treats the symptom.

Worth a gate either way: a cold-cache node:http compile-and-run in the tier
that already builds package smokes would have caught this, and would catch the
next instance of the same class.