refactor(subagent): drop host-user authority and split lifecycle publication

Remove the host-user continuation capability and the public residency query,
then separate the seam's public event payloads from its internal lifecycle
control interfaces.

`followup()` now takes the exact live direct parent `Agent` instead of a
`SubagentAuthority` union. No production adapter ever supplied user authority,
so the `UserAuthorityGrant` brand token existed only to stop a forged
discriminant from bypassing the direct-parent check — deleting the branch
retires the token, its mint method, and that attack surface together.

Narrowing `parent` from `Agent | undefined` to `Agent` removes three special
cases, including the path where a parentless epoch dispatched its lifecycle
events unscoped. Scoped-versus-global dispatch is now decided by the event, not
by whether a caller happened to have a parent.

`activationState()` had no caller; `ActivationState`, `ActivationObserver`, and
`ContinuationHost` are package-private.

New `src/lifecycle.ts` owns the contained emitter, the one-shot run observer,
and the Activation observer, while `SubagentRunInfo`/`SubagentRunEndInfo` move
to `src/types.ts` beside the other consumer-facing contracts. Those payloads are
public API — dsh-jsonrpc, hooks-claude, and the package invariant all consume
them — whereas the observer is a contract between two in-package collaborators,
so they no longer share a home merely for both being lifecycle-shaped. The
service keeps ownership of the scope carrier: `scopeTarget()` composes the
service's own context filter, so a narrowed stand-in would silently change
scope filtering.

Also drops now-unused dsh-tasks-local and dsh-tool-tasks dev dependencies, and
corrects the README claim that a pre-residency failure emits a terminal edge —
that path only ever rethrew.

scripts/gen-cordis-catalog.ts

@@ -160,13 +160,11 @@ export const LINK_MAP: Readonly<Record<string, string>> = {
   SkillSummary: 'skills.md',
   SaveTextSpill: 'spill.md',
   SpillRef: 'spill.md',
-  ActivationState: 'subagent.md',
   ContinuableCreateRequest: 'subagent.md',
   ContinuableCreateSpec: 'subagent.md',
   ContinuableStart: 'subagent.md',
   ContinuableStartSpec: 'subagent.md',
   CoordinatorMessageSource: 'subagent.md',
-  SubagentAuthority: 'subagent.md',
   SubagentFollowupOptions: 'subagent.md',
   SubagentProvider: 'subagent.md',
   SubagentRun: 'subagent.md',
@@ -286,8 +284,8 @@ export const TYPE_LINK_EXEMPTIONS: Readonly<Record<string, string>> = {
   PromptAssembly: 'assembly result is owned by packages/core/system-prompt/README.md',
   ResumeAgentOptions: 'agent resume contract is owned by packages/core/agent/README.md',
   SessionForkSource: 'service-local fork input is owned by packages/core/session/src/index.ts',
-  SubagentRunEndInfo: 'event-local snapshot is owned by packages/subagent/subagent/src/index.ts',
-  SubagentRunInfo: 'event-local snapshot is owned by packages/subagent/subagent/src/index.ts',
+  SubagentRunEndInfo: 'event payload contract is owned by packages/subagent/subagent/src/types.ts',
+  SubagentRunInfo: 'event payload contract is owned by packages/subagent/subagent/src/types.ts',
   TelemetryRecord: 'seam-local record contract is owned by packages/telemetry/session-telemetry/src/index.ts',
   WorkflowAgentEndInfo: 'event-local snapshot is owned by packages/workflow/workflow/src/index.ts',
   WorkflowAgentInfo: 'event-local snapshot is owned by packages/workflow/workflow/src/index.ts',

scripts/type-equiv.manifest.json

@@ -1104,21 +1104,11 @@
       "symbol": "SubagentFollowupOptions",
       "source": "packages/subagent/subagent/src/continuation.ts"
     },
-    {
-      "doc": "docs/core-data-structures/subagent.md",
-      "symbol": "SubagentAuthority",
-      "source": "packages/subagent/subagent/src/continuation.ts"
-    },
     {
       "doc": "docs/core-data-structures/subagent.md",
       "symbol": "ContinuableStart",
       "source": "packages/subagent/subagent/src/continuation.ts"
     },
-    {
-      "doc": "docs/core-data-structures/subagent.md",
-      "symbol": "ActivationState",
-      "source": "packages/subagent/subagent/src/continuation.ts"
-    },
     {
       "doc": "docs/core-data-structures/subagent.md",
       "symbol": "ContinuableCreateRequest",