Docs: add these prompts, I guess

docs/prompts/caller-posts-to-own-io-context.md

@@ -0,0 +1,7 @@
+# Caller post-back uses getSelf io_context
+
+Viral posting invokers resume the caller on the thread that issued `co_await`, using `callerIoContext` captured from `ComponentThread::getSelf()` at promise construction time.
+
+Dynamic `ExplicitPostTarget` only affects post-TO (`initial_suspend`), not post-back.
+
+See [post-to-and-back-in-invokables.md](post-to-and-back-in-invokables.md).