fix: data race with Kill() and Run()

[andrinoff]

What?

Fixes a crash that happens when Kill() is called immediately after Run(), before the program has finished starting up.

Why?

Fixes #1689

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.42%. Comparing base (930e18c) to head (016adb6).

Files with missing lines	Patch %	Lines
tea.go	80.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1774      +/-   ##
==========================================
+ Coverage   57.40%   57.42%   +0.01%     
==========================================
  Files          25       25              
  Lines        1324     1334      +10     
==========================================
+ Hits          760      766       +6     
- Misses        474      476       +2     
- Partials       90       92       +2     

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