npm runs the `postbuild` hook after every `npm run build`, and the desktop
compiler (scripts/build/desktop.mjs) already runs checkDistBuilt on the
scratch product before it publishes dist/. Every update and every pack
therefore re-verified the bytes it had just verified; with the per-chunk
syntax check that was a second ~960-process pass (#123216).
Drop the hook; nix's checkPhase calls the guard directly.
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