Interim update/thoughts:
I have pruned back the branches that were almost devoid of foliage, and examined the holes in those branches. All holes are about 60mm long and 5mm in diameter, ie. none of them extend into big galleries. They are also consistently in the centre of the branch, which probably leaves the branch with the greatest strength (it is a tube). All holes were empty.
The holes one sees on the outside are the same diameter as on the inside, so I am sure these are exit holes. ...or I would be if I had found a pupa inside. Having made the chamber, it would seem likely the moth would use its protection and pupate there. That's confirmed by this
diagram (figure D). Maybe the larvae were extricated by a predator of some sort (we don't have aye-aye in Cyprus!) Note that, in figure D, the pupal exit hole is at the top of the tunnel; none of the tunnels I have seen come out at the top. That may be consistent with predation at the larval stage.
...
Some pieces of the jigsaw don't seem to fit, yet...
Even if the larva was lost to predation, how come the hole on the outside is the same diameter as that inside? The larva must have chewed it out to that size. (The larva emerges from the egg laid near a leaf bud and bores through the bark when very small - so the entrance hole is tiny.) I can see that would be a good idea - to let its crass (faeces) fall out. So maybe that figure D is misleading; maybe the last chewing the larva does is final enlargement of the entrance hole, then after pupation and metamorphosis, the adult emerges from the pupa downwards (assuming it can turn around). And then maybe the remnants of the pupal case fall out - leaving the empty tunnel. That scenario would also be of benefit since rain water would have no chance of entering the tunnel.
Interesting little conundrum.
Still pondering...