test(subagent): drop the vacuous fork-dedup case; align wording with the header baseline

The dedup guard pinned 'no duplicate stamp' — under the header baseline no
stamping exists, so its event-count assertion became a tautology and its
fence assertions a subset of the stale-seed case. The spec docblock claimed
the session invariants pin the stamping design (superseded); it now names
the three review-found timing threats the suite pins as distinct shapes.
Service overrideOf JSDoc shrinks to a pointer at the owning pure export.

packages/ui/user-approval/src/index.ts

@@ -350,19 +350,12 @@ export class ApprovalService extends Service {
   }
 
   /**
-   * A session's approval-policy OVERRIDE — the override chain alone, never
-   * the configured default: the fold of the session's OWN switches (events
-   * past the seed boundary — a fork seed's stale parent switch is subsumed by
-   * the baseline captured after it), else the header's inherited delegation
-   * baseline. The subagent driver stamps `overrideOf(parent.session)` into
-   * each child's creation meta, so a `'never'` (headless/CI) parent cannot
-   * mint children that fall back to a prompting default, at any depth
-   * ([rationale](../../../.agents/notes/implemented/feature/2026-07-25-subagent-policy-inheritance.md)).
+   * {@link approvalOverrideOf} surfaced on the service, for consumers that
+   * reach the seam through `ctx.get('approval')` (the subagent driver's
+   * delegation capture) rather than a value import.
    * @param session - the session whose override chain to resolve.
    * @returns the effective override, or `undefined` for a session following
    *   the configured default.
-   * @throws when the durable header baseline is outside the closed policy
-   *   vocabulary (a corrupt or foreign log; durable-boundary validation).
    */
   overrideOf(session: Session): ApprovalPolicy | undefined {
     return approvalOverrideOf(session)