`config.default` becomes the composition base of an `agent-presets` settings
namespace, so the user document layers over the deployment's engineering
default and a person can change which preset new sessions get without a
restart.
The value is read per resolution rather than snapshotted: a hot-reloaded
document takes effect on the next session created, and every running session
stays on the preset it was composed from — which is the same rule the
session-header guard enforces from the other side.
`resolve()` read `config.default` directly, which would have made the whole
setting inert; it now goes through `defaultId` like every other caller.
The write-protection test is rewritten against a temp profile root. It was
passing vacuously: the un-overridden Loader REWRITES the composition it read —
stamping `disabled: true` onto the self-disposing row — so the committed
fixture had been mutated by the very run that proved the bug, and every later
run compared against the damaged file and passed. Building the preset in a
temp directory makes the assertion immune to its own failure mode, and it now
fails with a visible `+ disabled: true` when the override is removed.
Review follow-ups on this layer. The exported schema is
`AgentPresetSettingsSchema`, symmetric with the `AgentPresetSettings`
interface it resolves and self-describing at an import site. The `session.create`
JSDoc promised "the deployment's default preset" for an omitted `agentPreset`,
which this layer makes false — it now names the effective default. The
constructor records why it does not use `installSettingsSection`: that helper
re-judges what a consumer DERIVED across attach and detach, and nothing here is
derived. The provider-unload test disposes the fiber `ctx.plugin()` handed back
instead of reaching into `ctx.reflect.store`, and the write-protection wait says
why slack is the right shape for an absence assertion.
The real composition covers the layering too. `apps/cli` boots the shipped
`cordis.yml`, stores `agent-presets.default`, and asserts an unnamed session
composes from it — the package suite proves the layering against a hand-built
context, this proves the roster and the settings provider are wired to each
other. That test also pins the settings row at a temp file: it defaulted to
`$DSH_HOME/settings.yaml`, so a developer's own stored default decided the
outcome of a file whose whole point is that only the shipped root does.
The Agent Note records the per-resolution read and its correspondence with the
session header, and the vacuous-test finding above.
A preset publishes its services behind `isolate` realms, which is what
makes them per session — and what makes them invisible to every host
context. The api-proxy kept reading the root realm, so requests that are
ABOUT a session but arrive from outside it answered for a singleton that
no longer exists: `goal.pause`/`clear` and `skill.list` returned "this
deployment does not mount @deepseek-ai/dsh-goal / dsh-skill" for sessions
whose composition mounts exactly that. Verified against a running host
before and after.
`agentPresets.serviceFor(agent, name)` addresses the instance instead,
reading the same subtree-ownership relation `leakedServices` already
uses, inverted. It is read addressing for a caller holding the agent: a
host row that `inject`s a service cannot use it, because injection
resolves before any session exists — which is why `tools` and
`subagents` stay host-plane and this is not a way around that.
Tool presenters had the same shape and the same cure: `viewFor` looked
definitions up without a scope while the global layer is empty by
design, so every card degraded to the generic renderer. It now takes the
owning agent.
Cold resume through `agentFor()` mounted no preset at all, so every
generic entry point — prompt, models, commands — rebuilt a restarted
session on host tools and the deployment persona. It composes the
recorded preset now, as the other resume path already did.
A preset is a directory holding one `agent.cordis.yml`. Mounting it under an
agent's scope context during `setup(agentCtx)` gives that one session its own
tools and prompt sections while every other live session keeps its own.
No registry gains a tier. `dsh-tools` and `dsh-system-prompt` already file
registrations into the calling context's scope layer, and entry contexts chain
to the context a subtree was plugged into, so a composition mounted under
`agent.ctx` is that agent's alone and unwinds with it.
The mount audits itself because a directly-plugged subtree is absent from
`ctx.loader.entries()` and no boot audit covers it. It rejects an unscoped
target, a row that never became usable, and a row that published a service into
the root service realm — that last one is process-global rather than
per-session, and its collision with the next session surfaces as an unhandled
rejection `setup` never observes, leaving a half-composed agent that looks
healthy. The package invariant re-checks that rule on every service
notification, since a row publishing from a timer would escape a one-shot audit.
Raises the `packages/README.md` word ceiling from 920 to 980: the group table
must enumerate every group, and the new `preset/` row is necessary content.
Design: .agents/notes/implemented/architecture/2026-08-03-per-session-agent-presets.md
