Following up: I did ask ⚡️ᗪㄖ匚⚡️ (npub1xy5…3urc) in a separate note, and in the end I solved it myself.
The problem was how I had paired Clave with my MCP server: I used a nostrconnect link. Pairing through a bunker address (copied from Clave) fixes it, even from Termius on the same iPhone: with Clave in the background and low trust, the signing request now arrives and I can approve it in about 6 seconds.
Tested only a couple of times, but it works exactly in the setup that failed before. So there is no need for another signer, and no need for full trust.
