That error is correct. The namespace isn't matching the directory structure. If you click the suggestion for it the proper directory structure will be created. In this case would be src/cursive_shadow_cljs/core.cljs.
Those deps are out of date. Clojure is at at 1.10.2 and ClojureScript at 1.10.773.
Try File -> Invalidate Cache / Restart
You want the clojure and clojurescript deps in :deps at the root rather than a dev alias extra dep.
Here's an example deps.edn for a shadow-cljs project with reagent pulled in:
{:deps {org.clojure/clojurescript {:mvn/version "1.10.773"}
reagent/reagent {:mvn/version "1.0.0"}}
:paths ["src"]
:aliases {:dev {:extra-deps {binaryage/devtools {:mvn/version "1.0.2"}}}
:shadow {:extra-deps {thheller/shadow-cljs {:mvn/version "2.11.13"}}
:main-opts ["-m" "shadow.cljs.devtools.cli"]}}}
I'd recommend following the official user guide for current configuration: https://shadow-cljs.github.io/docs/UsersGuide.html
That looks like it might be a network error of some kind? I’m not sure what “Cannot reconnect” means otherwise.