agree with my kind nomic neighbor @Zach!
Workaround : the code is correctly browsable when clicking on "Tree" from last commit in commit list.
And now git-ssb-web won't see the repository at all, even on its original page. It just resolves it as empty.
I have realized my error: I forked a repository that's larger than 5MB, and there's no way to push it all at once.
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