Module Declarations are not Reactive - is this expected?

[oodavid]

Describe the bug
When following the Tutorial, the Module Context > Sharing Code lesson shows that module variables are shared between components of the same type.

There's nothing to say that module variables are not reactive - is this expected behaviour?

To Reproduce

I have a trite REPL example that shows no reactivity when module variables are modified:

https://svelte.dev/repl/369bc4ec3fbb4d81910d08aba96779a1?version=3.31.0

Expected behavior

Visually there's no clue that the following are fundamentally different.

This works as expected

<script>
  let foo;
  function updateFoo(bar) {
    foo = Math.random();
  }
  $: console.log(foo); // fine
</script>

This doesn't

<script context="module">
  let foo;
</script>
<script>
  function updateFoo(bar) {
    foo = Math.random();
  }
  $: console.log(foo); // not fine
</script>

A slight tangent

The second foo should throw a warning.

Paste this into a vanilla html document and you'd see Uncaught SyntaxError: Identifier 'foo' has already been declared

<script context="module">
  let foo;
</script>
<script>
  let foo;
</script>

Severity
More than anything, it surprised me. In the context of the tutorial, it's an 11th-hour edge-case / gotcha to be mindful of.

Idea
The compiler could / should complain about reactive statements related to module variables. I'd love to see this in the same vein of:

• A component can only have one <script context="module"> element
• A component can only have one instance-level <script> element

[oodavid]

Following on about compiler warnings, the idea could be generalised as:

this reactive statement will never be triggered / is unused

this means you could handle other edge cases too, ie:

const foo;
$: console.log(foo);

Via: https://discord.com/channels/457912077277855764/457912077277855766/794528287002329088

[Conduitry]

It is expected, and is described in the reference in the blue box in https://svelte.dev/docs#script_context_module but perhaps should also be mentioned in the tutorial

[oodavid]

Thanks.

Should I split out another issue for reactive statement warnings? Seems like I've really made two issues here.