Maybe that's a bit better for a user? Per live review, we think that's the only situation that can lead us to this assertion failing.
Also, this is non-blocking because extremely pedantic, but it might be nice to add an assert.<xxxxxx>.pass.cpp test to check that behavior. You can take inspiration of other tests like libcxx/test/libcxx/strings/basic.string/string.access/assert.back.pass.cpp.
Maybe you could initialize i to a non-zero value just to rule out the fact that we're accessing zeroed-by-chance memory that would be uninitialized below?
Maybe that's closer to what a user would actually write?