refactor(subagent): drop speculative effect rollback

The PR moved child scope-effect registration into the contribution-installation try/catch solely to cover a hypothetical throw, while documenting that Context.effect cannot reject for the live unpublished scope passed to apply. The change therefore added control-flow and rollback implications for a failure mode the API does not expose, without changing observable behavior.

Keep the rollback boundary focused on contribution installers, which are the operations that can actually fail and leave recorded installations to unwind. Register the child-scope cleanup effect immediately after that boundary, as before; its disposer still converges with contribution removal through the registry idempotence rules.

This is a behavior-preserving removal of unnecessary code. The focused activation-setup-registry suite passes all 11 tests, the subagent TypeScript project checks cleanly, and the staged diff passes whitespace validation.

packages/subagent/subagent/src/activation-setup-registry.ts

@@ -113,10 +113,6 @@ export class SubagentActivationSetupRegistry {
         // Dispose that escaped record and invalidate the provisioning batch.
         if (isRemoved(registration)) this.release(installation)
       }
-      // Register the scope-disposal release inside the same try so the
-      // setup-rollback catch also covers a hypothetical effect-registration
-      // throw; today effect() cannot reject on a live unpublished scope.
-      childCtx.effect(() => () => { this.releaseChild(childCtx) }, 'subagents.activationSetup()')
     } catch (error: unknown) {
       // Keep the installer failure authoritative, but attempt every rollback.
       try {
@@ -127,6 +123,7 @@ export class SubagentActivationSetupRegistry {
       }
       throw error
     }
+    childCtx.effect(() => () => { this.releaseChild(childCtx) }, 'subagents.activationSetup()')
     return {
       commit: () => {
         if (state.invalidated) {