fix(scope): close final ownership races

Drain idle injection flushes before agent teardown, snapshot approval and subagent provider inputs, and gate subagent lifecycle events on real child readiness. Align the RFCs and generated contracts with the hardened behavior.

packages/core/agent-loop/tests/scope-lifecycle.spec.ts

@@ -440,4 +440,35 @@ describe('agent scope lifecycle', () => {
     expect(ctx.sessions.get(SessionId('h1-s'))).toBeUndefined()
     await unload
   })
+
+  it('handle.dispose() awaits an idle-injection flush before unregistering or detaching', async () => {
+    const ctx = await harness()
+    const handle = await ctx.agents.create({
+      agentId: AgentId('idle-flush'),
+      sessionId: SessionId('idle-flush-s'),
+      agentOptions: { model: 'mock' },
+    })
+    const gate = Promise.withResolvers<undefined>()
+    let flushStarted = false
+    ctx.on('session/flush', (session) => {
+      if (session !== handle.agent.session) return
+      flushStarted = true
+      return gate.promise
+    })
+
+    handle.agent.inject(text('durable idle context'), { source: { kind: 'plugin', plugin: 'test' } })
+    expect(flushStarted).toBe(true)
+
+    let disposed = false
+    const disposal = handle.dispose().then(() => { disposed = true })
+    await new Promise(resolve => setTimeout(resolve, 0))
+    expect(disposed).toBe(false)
+    expect(ctx.agents.get(AgentId('idle-flush'))).toBe(handle.agent)
+    expect(ctx.sessions.get(SessionId('idle-flush-s'))).toBe(handle.agent.session)
+
+    gate.resolve(undefined)
+    await disposal
+    expect(ctx.agents.get(AgentId('idle-flush'))).toBeUndefined()
+    expect(ctx.sessions.get(SessionId('idle-flush-s'))).toBeUndefined()
+  })
 })