fix cache.addAll and cache.add hanging

[KhafraDev]

Fixes #5615

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[KhafraDev]

I tried using Claude to help me investigate this issue. Big mistakes. Sometimes this technology feels like magic and sometimes it feels like it took me longer to diagnose the bug with it than without. It tries cutting corners whenever it can no matter how strongly I try prompting/guiding it. It definitely reaffirmed by belief that it shouldn't touch the web specs in any way, shape, or form yet, unless Opus 5 is generally suckish (I use it over Fable for the much better usage limits).

The AI issue also blames #3093 for this despite it NOT being the cause, which steered me away from the actual cause for a bit. 🫠

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.23810% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.88%. Comparing base (164a354) to head (67575b7).

Files with missing lines	Patch %	Lines
lib/web/fetch/index.js	94.73%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5844      +/-   ##
==========================================
+ Coverage   93.52%   93.88%   +0.35%     
==========================================
  Files         110      110              
  Lines       39773    39800      +27     
==========================================
+ Hits        37199    37367     +168     
+ Misses       2574     2433     -141     

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[mcollina]

lgtm