7 integration tests in client.test.ts skipped during Bun migration (hangs/timeouts)

[evans-sam]

Summary

During the Bun migration, 7 integration tests in `test/client.test.ts` (14 counting `SOAP Client` / `SOAP Client (with streaming)` variants) were marked `it.skip` because they hang past the 5s timeout without calling `done()`. Root cause is not the Bun migration itself — the tests have never actually run on this codebase (lib/ had ERR_MODULE_NOT_FOUND, see #43). Bun is the first environment to actually execute them.

Skipped tests

1. `should issue async callback for cached wsdl`
2. `should issue async promise for cached wsdl`
3. `should allow passing in XML strings`
4. `should send binary attachments using XOP + MTOM` (Binary attachments handling)
5. `Should preserve SOAP 1.2 "action" header when sending MTOM request`
6. `Should send MTOM request even without attachment`
7. `should add proper headers for soap12` (Headers in request and last response)

Symptom pattern

All failures share the shape:

```
(fail) SOAP Client > [5000.XX ms]
^ this test timed out after 5000ms, before its done callback was called.
```

No assertion failure is raised — the callback chain from `soap.createClient` / `client.MyOperation` never completes. Server is started, request is presumably issued, but no response/error reaches the SOAP callback.

Likely categories

• Cached-wsdl async callback: asserts the callback fires after the synchronous `assert(!called)` check, i.e., that `soap.createClient` schedules its callback asynchronously even when the WSDL is already cached. May indicate a src path that resolves synchronously from cache, breaking the expectation, or the opposite (never firing).
• MTOM / binary attachments / soap12 headers: integration paths that exercise the src/http.ts response-parsing code for multipart content-types or specific header handling. May have real src/ defects that were never caught because the suite never ran.
• XML string passing: client.MyOperation with `_xml` string argument — sends raw XML, server returns pre-baked envelope. Should exercise the simplest possible send/receive but times out.

Reproduction

```
bun test test/client.test.ts -t "should issue async callback for cached wsdl"
bun test test/client.test.ts -t "should allow passing in XML strings"

etc.

```

Each hangs for exactly 5000ms before timing out.

Suggested investigation

1. Remove one `.skip` at a time and run with `--timeout 30000` + `BUN_TEST_TRACE_EVENTS=1` or similar to see where the callback chain stops.
2. Compare what happens under node (via the published lib/ once Published lib/ uses extensionless ESM imports; pure Node consumers hit ERR_MODULE_NOT_FOUND #43 is fixed) — if tests pass there, the issue is Bun-specific runtime behavior. If they fail there too, it's pre-existing src/ bugs exposed by tests actually running.
3. Likely suspects per category:
   • cached-wsdl: `src/soap.ts` / `src/client.ts` WSDL cache retrieval path.
   • MTOM: `src/http.ts` multipart response parsing, `parseMTOMResp` — note the `if (!boundary)` branch calls `callback(err); throw err;` which was a known pattern (see commit d18c520 for the similar issue in the main catch handler).
   • XML string: `client.MyOperation({ _xml: xmlStr }, ...)` path in `src/client.ts`.

Context

This issue is a checklist of investigations, not a single-PR fix. Each skipped test likely has its own root cause. Unblocks removing the `.skip` markers added in commit 00b0b6b.

Related: #43 (extensionless lib/ imports), #45 (err.root on non-Fault parse errors).