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

[Jimbo4350]

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.

[Jimbo4350]

Re-based branch: master...leios-prototype-2026-08-13

@ch1bo would need to resolve the resolver conflicts.

[palas]

New re-based and re-organised branch: master...leios-prototype-rebased