How do I access the stash from a plugin?

Use the accessor  $context->stash as documented?

Why can't I access the stash like I am now?

I'm guessing (because your snippet isn't demonstrative) that by the time you try to access it, it probably doesn't exist anymore :)

Does Template::Plugin::Stash work for you?

$ cat stash.tt
[% USE Stash %]
[% USE Dumper Indent = 1 %]
[% Dumper.dump( Stash.stash()  ) %]


$ tpage --define foo=bar stash.tt


$VAR1 = {
  'global' => {},
  'foo' => 'bar'
};
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