refactor(scope,agent-presets): per-preset standing mounts over a scope parent chain

A preset is now ONE composition per process, not one per session. The roster
mounts it once under a synthetic standing scope; each agent joins by having
its scope key parented to the mount's. Two mechanisms in dsh-scope carry the
whole change: registration views walk the parent chain (global → preset →
agent, nearest shadowing farthest — ScopedLayers.chainLayers), and scoped
event dispatch admits a listener tagged with an ancestor of the carrier key,
which is what lets a standing composition's plan/compaction/token listeners
observe each agent composed under it while a sibling preset's stay deaf.

The preset plugins already key their state by Session/Agent — they predate
presets and were written for the shared world — so sharing one instance is a
return to their design, not a rewrite. Preset ymls are unchanged: one mount
per preset means one Entry per preset, whose entry-local realms keep two
presets' services apart exactly as they kept two sessions' apart before.

The standing scope hangs off the service's UNTRACED context (selfCtx): a
method invoked through the traceable proxy sees this.ctx rebound to the
caller and carrying its shadow, and a subtree minted from that resolves every
service through the shadow's fiber instead of each entry's own inject store —
preset rows then fail on the very services they declare.

A standing mount survives its agents deliberately. The composition a running
session joined must outlive the file changing or disappearing underneath it;
reclamation happens at whole-tree teardown, and file edits reach only future
generations (the authoring layer swaps the pointer, never disposes a joined
generation).

packages/preset/agent-presets/src/index.ts

@@ -1,17 +1,29 @@
 /**
  * Agent presets: each session composes its model-facing plugin set from one
- * preset `cordis.yml` mounted under that agent's scope context.
+ * preset `cordis.yml`, mounted ONCE per preset under a standing scope and
+ * joined by every agent that names it.
+ *
+ * The standing mount is what makes a preset one composition rather than one
+ * per session: its plugin instances, tool registrations, prompt sections, and
+ * projection units exist exactly once, keyed per session inside the plugins
+ * themselves (they predate presets and were written for a shared world). An
+ * agent joins by having its scope key parented to the mount's
+ * ({@link setScopeParent}), which makes the mount's registrations visible to
+ * that agent's views and the mount's listeners receive that agent's events —
+ * and a host reader with no agent at all (a cold transcript read) resolves
+ * the same standing registrations by preset id.
  *
  * This package owns the preset vocabulary, filesystem discovery, and the
- * guarded mount. It does not decide when an agent is created — the agent
- * factory's `setup(agentCtx)` hook is the one supported call site, because
- * only there is the composition installed while the agent is still
- * unpublished, so a rejected mount rolls the whole creation back.
+ * guarded standing mount. It does not decide when an agent is created — the
+ * agent factory's `setup(agentCtx)` hook is the one supported call site,
+ * because only there is the join installed while the agent is still
+ * unpublished, so a rejected composition rolls the whole creation back.
  * @module @deepseek-ai/dsh-agent-presets
  */
 
 import { Context, Service } from 'cordis'
 import z from 'schemastery'
+import { createScope, scopeOf, setScopeParent, type Scope, type ScopeKey } from '@deepseek-ai/dsh-scope'
 import { discoverPresets } from './discovery.ts'
 import { mountPreset } from './mount.ts'
 import type { AgentPreset, Config } from './types.ts'
@@ -45,8 +57,19 @@ export class AgentPresets extends Service {
     })).default([]),
   }) as z<Config>
 
+  /**
+   * The service's own untraced context. Methods invoked through the traceable
+   * proxy see `this.ctx` rebound to the CALLER's context, which carries a
+   * shadow; a subtree minted from it resolves every service through that
+   * shadow's fiber instead of each entry's own inject store, so preset rows
+   * would fail on the very services they declare. Standing mounts must hang
+   * off the untraced original (the `tasks-local` selfCtx precedent).
+   */
+  private readonly selfCtx: Context
+
   constructor(ctx: Context, public config: Config) {
     super(ctx, 'agentPresets')
+    this.selfCtx = ctx
   }
 
   /** The preset id mounted when a caller names none. */
@@ -80,21 +103,67 @@ export class AgentPresets extends Service {
   }
 
   /**
-   * Compose one agent from a preset, installing it under that agent alone.
+   * Standing mounts by preset id, single-flight so two agents racing the
+   * first use of one preset share one composition. A settled failure is
+   * removed so a later session retries a preset whose file has been fixed; a
+   * settled success is permanent for the process — the composition a running
+   * session joined must survive the file changing or disappearing underneath
+   * it, so file edits reach only future generations (a later authoring layer
+   * swaps this pointer; it never disposes a joined generation).
+   */
+  private readonly standing = new Map<string, Promise<StandingMount>>()
+
+  /**
+   * Compose one agent from a preset: ensure the preset's standing mount, then
+   * parent the agent's scope key to it so the mount's registrations and
+   * listeners cover this agent.
    *
    * Call from the agent factory's `setup(agentCtx)`; a rejection there rolls
    * the agent creation back, so a broken preset never yields a half-composed
    * session.
    * @param agentCtx - the agent's scope context.
    * @param id - the preset id, or `undefined` for {@link defaultId}.
-   * @returns the preset that was mounted, for the caller to record.
+   * @returns the preset that was composed, for the caller to record.
    * @throws when the preset is unknown or its composition is unusable.
    */
   async mount(agentCtx: Context, id?: string): Promise<AgentPreset> {
+    const agentKey = scopeOf(agentCtx)
+    if (agentKey === undefined) {
+      throw new Error('agent-presets: refusing to compose an unscoped context; the scope key is what joins an agent to its preset')
+    }
     const preset = await this.resolve(id)
-    await mountPreset(agentCtx, preset)
+    const standing = await this.ensureStanding(preset)
+    setScopeParent(agentKey, standing.key)
     return preset
   }
+
+  /** Resolve (or create, single-flight) the standing mount of one preset. */
+  private ensureStanding(preset: AgentPreset): Promise<StandingMount> {
+    const pending = this.standing.get(preset.id)
+    if (pending !== undefined) return pending
+    const created = (async (): Promise<StandingMount> => {
+      const key: ScopeKey = { agentPreset: preset.id }
+      const scope = createScope(this.selfCtx, key)
+      try {
+        await mountPreset(scope.ctx, preset)
+      } catch (error) {
+        this.standing.delete(preset.id)
+        await scope.dispose()
+        throw error
+      }
+      return { key, scope }
+    })()
+    this.standing.set(preset.id, created)
+    return created
+  }
+}
+
+/** One preset's standing composition. */
+interface StandingMount {
+  /** Scope key agents are parented to; also the mount's registration scope. */
+  readonly key: ScopeKey
+  /** Disposal boundary; held for whole-tree teardown, never per-session. */
+  readonly scope: Scope
 }
 
 export default AgentPresets

packages/preset/agent-presets/src/mount.ts

@@ -185,8 +185,9 @@ export async function mountPreset(agentCtx: Context, preset: AgentPreset): Promi
     )
   }
   const config: Include.Config = { path: pathToFileURL(preset.path).href }
-  // Before the record this mount is about to add: every session takes this
-  // path, so it is what keeps the set bounded on a host that never reads it.
+  // Before the record this mount is about to add: standing mounts are one per
+  // preset and live until whole-tree teardown, so pruning here only sweeps
+  // records of torn-down runtimes (tests; an HMR reload of the roster).
   pruneDisposedMounts()
   const handle = agentCtx.plugin(PresetTree, config)
   try {

packages/preset/agent-presets/tests/invariant.spec.ts

@@ -38,7 +38,7 @@ async function harness(): Promise<Context> {
 }
 
 describe('agent-presets invariants', () => {
-  it('tracks a mounted composition and forgets it once the agent is gone', async () => {
+  it('keeps the standing composition alive across the agents that joined it', async () => {
     const ctx = await harness()
     const handle = await ctx.agents.create({
       sessionId: SessionId('inv-live'),
@@ -47,8 +47,20 @@ describe('agent-presets invariants', () => {
 
     expect(livePresetMounts().map(mount => mount.presetId)).toContain('standard')
 
+    // A standing mount survives its agents: the composition a session joined
+    // is shared, so one session ending must not strip it from the next.
     await handle.dispose()
+    expect(livePresetMounts().map(mount => mount.presetId)).toContain('standard')
 
+    // A second agent reuses the same mount rather than adding one.
+    await ctx.agents.create({
+      sessionId: SessionId('inv-live-2'),
+      setup: async (agentCtx: Context) => void await ctx.agentPresets.mount(agentCtx, 'standard'),
+    })
+    expect(livePresetMounts().filter(mount => mount.presetId === 'standard')).toHaveLength(1)
+
+    // Whole-tree teardown is the boundary that does reclaim it.
+    await ctx.fiber.dispose()
     expect(livePresetMounts().map(mount => mount.presetId)).not.toContain('standard')
   })