As for LSP specifically, and in particular for Q2 & Q3: You are correct, those were meant to be very specific to session management and capabilities of existing, established protocol implementations of LSP. Would an implementation of those work without modifying editors? Looking at VSCode, LSP seems to be more of a guideline and it expected to provide your own LSP client plugin anyway, so it probably is less of a problem there. But some editors (e.g. Helix and Emacs) apparently have their official implementation.