91b55b9245
`session.create` takes an optional `agentPreset`, and the host resolves it, mounts it during pre-publication setup, and records the resolved id on the session header so a later resume rebuilds the same agent. Resolution happens BEFORE the session exists, not inside setup: the session boundary snapshots `meta` before asynchronous setup begins, so an id discovered during setup could never reach the header. Mounting still happens in setup, where a failure rolls the whole creation back rather than publishing a session whose capabilities are half-installed. Resume ignores whatever the request names and rebuilds from the stored id. A resumed session's history was produced under that composition; restoring a different one would replay tool calls the model can no longer make. `dsh-agent-presets` now throws `UnknownPresetError` / `PresetMountError` so the host can tell a bad request from a broken preset — they become `agent-preset-not-found` and `agent-preset-invalid`. Ships the two built-in compositions (`standard`, `core-web`) and the persona row that lets them differ in identity. Nothing mounts them yet: no roster is configured, so `composeAgent` finds no service and every session keeps the host composition. Wiring the roster and moving base's agent-plane rows behind it is the next commit, so the switch happens atomically with a real-composition test.
preset/ — per-session agent composition
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An agent preset is a directory holding one agent.cordis.yml. Mounting it under an agent's scope context gives that session its own tools and prompt sections while every other live session keeps its own, so one process can run several differently composed agents at once.
| Package | Role | ctx key |
|---|---|---|
agent-presets/ |
Preset vocabulary, filesystem discovery over trusted and user-authored roots, and the guarded per-agent mount | ctx.agentPresets |
persona/ |
The agent persona as a composable row, so a preset can change identity and not only tools | — |
The composition split this group assumes: registries and cross-session facilities are process singletons and stay in the host composition, while a preset carries what one agent contributes to them. A preset that names a row publishing a process-global service is rejected at mount rather than allowed to collide with the next session.
Design: the per-session agent-preset note.