doc: warn against awaiting replies in module hooks

Awaiting a reply from the registering thread inside a resolve or load
hook deadlocks: resolution is synchronous from that thread's
perspective, so it is blocked in the request and cannot answer.

Fixes: #63085
Signed-off-by: Paul Bouchon <mail@bitpshr.net>
PR-URL: #65590
Reviewed-By: Jacob Smith <jacob@frende.me>

Author: bitpshr

doc/api/module.md

@@ -1282,6 +1282,13 @@ register('./my-hooks.mjs', {
 });
 ```
 
+A hook can send messages to the thread that registered it at any time, as
+above. It must not block on a reply from that thread: resolution and loading
+are synchronous from the perspective of the thread that triggered them, so that
+thread is blocked until the hook settles and cannot answer in the meantime.
+Hooks can otherwise be fully asynchronous; it is only a reply over this
+message channel that cannot be awaited.
+
 #### Asynchronous hooks accepted by `module.register()`
 
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