Upstream non-Leios commits from the Leios integration branch to master

**Before starting: confirm with Sebastian Nagel which Leios integration branch is the relevant one** (`leios-prototype`, `jl/leios-prototype-remake`, and `sl/leios-prototype-remake` all exist).

The Leios integration branch carries a mix of Leios-specific work and changes that are not Leios-specific — Dijkstra-era enablement and general fixes among them. The latter belong on master: carrying them on the prototype branch makes every rebase harder and delays code master wants anyway.

Task:
- Confirm the relevant branch with Sebastian.
- Audit its commits and identify everything that builds against released dependencies (no leios SRPs required).
- Bring those changes onto master via normal PRs — cherry-pick where the commits apply cleanly, or manually integrate where they don't.
- Rebase the Leios branch so it carries only Leios-specific work.