fix(vtz): node:http hang — graceful shutdown + sync .then() bug (resolves #2718, #2720)

[viniciusdacal]

Root cause

The synthetic node:http module's createServer().listen() treated globalThis.__vtz_http.serve() as asynchronous — but serve() is a synchronous op that returns the server object directly. The resulting .then(...) on a non-thenable threw a TypeError that was swallowed by the idiomatic new Promise((resolve) => server.listen(0, resolve)), so the listen callback never fired and tests hung at the 120 s watchdog. The CJS require('http') shim had the same bug.

Fixing the shim exposed three more defects in the underlying op layer:

1. op_http_serve_close aborted the tokio task immediately, cancelling in-flight axum handler futures mid-response so fetch() never got its reply.
2. op_http_serve_respond keyed the pending-responses map per server — replying after close (which removed the ServerInstance from state) silently dropped the response.
3. op_http_serve_accept / op_http_serve_respond threw "Unknown server id" when the accept loop re-polled after close, poisoning the event loop and corrupting unrelated tests.

What changed

Rust (native/vtz/src/runtime/ops/http_serve.rs)

• Replaced the abort-handle teardown with axum's with_graceful_shutdown(...) signal so existing connections drain cleanly.
• Moved pending_responses onto HttpServeState and keyed it globally by request_id so in-flight replies still work across close.
• Made op_http_serve_accept and op_http_serve_respond tolerate a missing server id (null / no-op) instead of throwing.
• Added two unit tests covering graceful shutdown of an in-flight response and the no-error contract after close.

JS (native/vtz/src/runtime/module_loader.rs, both NODE_HTTP_MODULE and the CJS http shim)

• Treat __vtz_http.serve() as synchronous.
• listen(cb) fires the callback via queueMicrotask (proper Node-async semantics).
• close(cb) defers the callback until all in-flight requests finish; connections received after close() return 503 without entering the user handler.
• Added the stock no-op event-emitter surface (on, once, off, emit, unref, ref) that callers expect.
• address() returns null before listen() completes, matching Node.

Tests

• Restored previously-quarantined packages/ui-server/src/__tests__/node-handler.test.ts and packages/docs/src/__tests__/docs-cli-actions.test.ts from .local.ts — both now pass under vtz test (26 + 11 tests, all green).
• New regression suite at packages/vertz/__tests__/node-http.test.ts with 5 scenarios covering listen(0) callback firing, buffered serve, empty-pending close, deferred close with an in-flight request, and bind failure reporting.
• Two new Rust unit tests in http_serve.rs (test_http_serve_graceful_shutdown_preserves_in_flight_response, test_http_serve_close_does_not_throw_unknown_server_id).
• Removed the test:integration npm scripts that existed purely to run these files under bun; image-processor.local.ts stays (NAPI, out of scope).

Quality gates

• cargo test -p vtz --lib — 3452 passing, 0 failing
• cargo clippy -p vtz --all-targets -- -D warnings — clean
• cargo fmt --all -- --check — clean
• vtz test in packages/ui-server (node-handler, 26 pass)
• vtz test in packages/docs (263 pass)
• vtz test in packages/vertz (21 pass incl. 5 new)
• tsgo --noEmit in ui-server, docs, vertz — clean

Note: the pre-existing test_inspect_brk_unblocks_after_debugger_connects flake under concurrent cargo test --all is unrelated; it passes in isolation.

Public API changes

None — internal runtime behavior only. Fixes bugs, no new surface.

Test plan

• Regression suite covers the hang scenario end-to-end via public node:http API
• Rust unit tests cover the graceful-shutdown + post-close response paths
• Restored quarantined .test.ts files exercise node:http in anger (SSR tests with dozens of buffered + streaming requests per test run)