dd1 is 4 (5 in August)
we have had insecure phases forever, and have tried various things to ride them out.
she used to eb ok being in her room form bedtime until whenever she went to sleep - singing, reading, looking out of the window etc. and then at times it would all go wrong, for no reason in particular, and we had to find other ways to deal with it.
we have been told, you have two choices - give in straight away (to avoid giving the wrong impression when you give in after lots of screaming), or ride it out. it depends on the situation which one we use.
if dd1 is having a tantrum (meltdown, really, but say that to convey what it might be over - eg wanting ice cream) then we are happy to ride it out.
if she is actually distressed over something (even though we don't know what), we give in. her fears, though not always apparent to us, are real to her, and I would not leave dd2 scared of something, or distressed by something, so tha tis my boundary line.
which is what led to us sleeping in her room, but we have cured her terror of being in her bedtroom.
we stayed with dd1 in her room because she was scared of being there herself (no idea why). she would scream the place down, and repeatedly come out of her room. when out of her room, she would be calmer, but would not be able to settle to sleep 9only ever sleeps in her room) as too stimulating all around her.
so, we needed to keep her in her room, but find a way to stop her panicking and screaming, which she had come to associate with being in her room.
so we stayed wiht her - completely wrong footed her, as she wasn't expecting it. we didn't interact at all - just like your dh last night. just sat there and pretended to go to sleep (dh actually does go to sleep - I wish i had his ability to just sleep at will ) until she slept, no matter what she was doing. we do not try to keep her on her bed, or keep her quiet, just let her read/sing/self settle util she falls asleep.
we have also put dd1 and dd2 in the same room, as this solves another issues for us as we go away a lot, but this is incidental, and hasn't affected dd1 at all.
once she was calm with staying in her room, we started moving slowoly to the door. again, no interaction, no actual movement that she could see, just set up our camp a little closer to the door each night.
then in the doorway, then outside the door, etc.
she has been fine with it, and we have committed to staying until she is asleep each night, which has really calmed her down (is a PITA, bt tbh, if it soves the issue, then it is better than endless nights of us tearing our hair out). she normally falls asleep around 9.30/10pm ish, so it is not an easy evening for us (they go to bed around 7ish) but the aim is to get her comfortable being in the room alone (well, with dd2 now) and the door closed agian, and doing her stuff until she falls asleep, which is essentially what is happening now, albeit with a safety net for her.