They have to use one key per app, otherwise independent app could end up sharing some permissions (IIRC).
The Emacs version for Android makes uses of something like this IIRC by signing a version of Termux with the same key and distributing it in the same SourceForge repo such that Emacs on Android can access CLI tooling like git for example.
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The Emacs version for Android makes uses of something like this IIRC by signing a version of Termux with the same key and distributing it in the same SourceForge repo such that Emacs on Android can access CLI tooling like git for example.