Hmm, it seems to be intentionally limited.

ve.ui.mwWikitextTransferRegistry.register(
	'internalLink',
	// [[...]] on a single line of max 80 characters
	/\[\[.{1,80}\]\]/m
);

https://gerrit.wikimedia.org/r/#/c/275193/ doesn't explain why :(

I think @cscott did this for performance.

Right, so this was actually introduced in https://gerrit.wikimedia.org/r/#/c/230146/, but that doesn't explain why either. Originally it just checked for no newlines (without a length limit), this was changed in PS3, but I didn't find a rationale for it in the comments.

For template detection, we just look for '{{'. I'm pretty sure we could do the same for links, looking for '[['. Neither is likely to occur in normal text.

In T151646#2832480, @Jdforrester-WMF wrote:

We could bump that to 250 or whatever but it could still be longer… If only MW used hashes rather than names to refer to images. ;-)

For this specific use case, it would have to be at least 526, by my count. And that would be silly.

Change 324514 had a related patch set uploaded (by Bartosz Dziewoński):
ve.ui.MWWikitextTransferRegistry: Just look for '[[' when detecting links

https://gerrit.wikimedia.org/r/324514

Change 324514 merged by jenkins-bot:
ve.ui.MWWikitextTransferRegistry: Just look for '[[' when detecting links

https://gerrit.wikimedia.org/r/324514