fix: be able to invoke Close in SSE callback

[invzhi]

fix #1047

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.85%. Comparing base (66256ef) to head (43dfdd1).
⚠️ Report is 5 commits behind head on v3.

Additional details and impacted files

@@            Coverage Diff             @@
##               v3    #1048      +/-   ##
==========================================
+ Coverage   99.82%   99.85%   +0.02%     
==========================================
  Files          18       18              
  Lines        3919     3361     -558     
==========================================
- Hits         3912     3356     -556     
+ Misses          5        3       -2     
  Partials        2        2              

Flag	Coverage Δ
unittests	99.85% <100.00%> (+0.02%)	⬆️

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