fix(subagent): pin delegated child approvals to 'never' within the inherited sandbox scope

A delegated in-process child now acts only within the sandbox scope fixed
at delegation: captureDelegatedPolicyOverrides still snapshots the parent's
explicit sandbox override but pins the child approval policy to 'never'
(instead of inheriting the parent's), so every child ask — sandbox_permissions
escalations included — is rejected deterministically by ApprovalService
before any answerer, with the audit pair still logged. Every in-process
child additionally receives the scoped subagent:delegation runtime-context
statement telling it to report a scope limitation instead of retrying.

Supersedes the approval half of the policy-inheritance decision (new Agent
Note cross-linked from both prior notes and the approval-seam Q&A); refreshed
child snapshot fixtures carry the pinned event, and
subagent-published-run-failure now persists a one-event child log.

packages/subagent/subagent-inprocess/tests/structured.spec.ts

@@ -247,10 +247,11 @@ describe('in-process structured output', () => {
     const result = await run.result
     expect(result.stopReason).toBe('error')
     expect(result.structured).toBeUndefined()
-    // Exactly one model request and one user message: no nudge turn exists.
+    // Exactly one model request and one caller-supplied user message (the
+    // delegation runtime-context snapshot aside): no nudge turn exists.
     expect(adapter.requests.length).toBe(1)
     const child = ctx.agents.get(run.id)!
-    expect(child.session.events.filter(e => e.type === 'user/message').length).toBe(1)
+    expect(child.session.events.filter(e => e.type === 'user/message' && e.data.source.kind !== 'plugin').length).toBe(1)
     await run.dispose()
   })