The Agent Note was written when only the seam existed and never caught up.
Rewritten in place, per the implemented-note contract, with the four facts the
later work established:
- a preset file is an INPUT: `EntryTree.write()` persists a tree whenever the
Loader thinks the config changed, and a self-disposing plugin is enough, so
the inherited behaviour truncates a shipped preset to `[]` the first time a
session ends
- a plugin that looks itself up in the global registry breaks inside a preset,
because `register()` files into the calling context's scope — the general
rule behind the `dsh-tool-skill` fix
- an entry-local `isolate` realm is invisible to the agent's own scope too, not
only to the host, which is what makes a preset's registry that agent's own
and also why a consumer left outside the group silently contributes nothing
- switching is blank-only, and why it swaps the subtree rather than the session
`docs/architecture.md` gains an Agent Presets section: the map has to carry a
new architectural concept or it is wrong, and the root layout gains the group.
Both budget ceilings are raised rather than the content cut. `AGENTS.md` sat at
1774/1775 — one word of room, already far under the 5% headroom the standard
asks for — so no group line could be added at all; `architecture.md` was in the
same shape. Raising restores headroom instead of encoding "the map may not grow".