fix(agent-loop): address review — quiet-item parking, meta, discard balance

Resolve six review findings on the unified-send change:
- quiet (wakeup:false) queued items no longer un-park the driver; the
  inbox distinguishes hasWakingQueued (drives the loop, idle/quiescence)
  from hasQueued (anything to dequeue), so a lone quiet item parks at idle
  and rides the next waking send. whenIdle/cancel settle off the waking
  signal, so cancelling a parked quiet item no longer hangs whenIdle.
- SendOptions.meta on queued/steering sends now reaches the durable
  user/message and steering/message (was dropped except on injection).
- a terminal agent/turn-stop that drops pending steering emits
  agent/inbox/discard so the enqueue-dequeue-or-discard ledger balances.
- the loop-authored continuation reason is snapshotted and frozen like a
  public send.
- gen-cordis-api collects exported classes (body-stripped) so the now-
  abstract-class Agent and its transitive shapes reappear in the API
  catalog.

Adds regression tests for each and re-records the affected snapshot.

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

@@ -526,6 +526,28 @@ describe('agent loop', () => {
     expect(agent.session.events.some(event => event.type === 'user/message' && event.data.source.kind === 'plugin')).toBe(false)
   })
 
+  it('preserves SendOptions.meta on the durable user/message and steering/message', async () => {
+    const adapter = new MockAdapter([toolCallResponse('c1', 'noop', {}), textResponse('done')])
+    const ctx = await harness(adapter)
+    ctx.tools.register(defineContentToolFixture({
+      name: 'noop', description: '', parameters: {},
+      async execute() {
+        // Running steer carries its own meta onto the durable steering/message.
+        agent.steer([{ type: 'text', text: 's' }], { source: { kind: 'plugin', plugin: 'p' }, meta: { steer: 1 } })
+        return []
+      },
+    }))
+    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
+
+    agent.send([{ type: 'text', text: 'go' }], { target: 'next-turn', wakeup: true, meta: { prompt: 1 } })
+    await waitForIdle(ctx, agent)
+
+    const user = agent.session.events.find(e => e.type === 'user/message')
+    expect(user?.type === 'user/message' && user.data.meta).toEqual({ prompt: 1 })
+    const steering = agent.session.events.find(e => e.type === 'steering/message')
+    expect(steering?.type === 'steering/message' && steering.data.meta).toEqual({ steer: 1 })
+  })
+
   it('agent/turn-continuation can force-continue (/loop pattern) and force-stop', async () => {
     // force-continue: model never calls tools, but a plugin forces 3 steps
     const adapter = new MockAdapter([