fix: ensure fork always accesses correct values

[dummdidumm]

Not all batches will flush right after being activated, some will be activated and then get is called on a signal. In that case the value was wrong because we did not apply the changes of that batch. By doing this.apply() during activate() we ensure we do, which fixes (among other things, likely) a forking bug where old values where sneaking in.

Fixes #17079

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