I think it was quite insensitive to roll out new URL scheme without backward compatibility for the old one, leaving plenty no-longer links behind. I hope it is easy to at least restore compatibility for direct commit links.
I can also help with finding out the mapping rules if you let me know what technology would be used for this (mod_rewrite or something else?).
See also #3619.
We don't need two tickets for this. Discussion can be in 3619...
In short this was fragile and broke all kinds of things.