feat(agent): Pi subagents via agent.spawn / agent.await

- agent_run gains depth / spawn_reason (0029); agent_run_event types
  subagent_spawned / subagent_event / subagent_completed
- agent.spawn (propose, medium, replay never): allowlist ⊆ parent, mode not
  above parent, budget carved from parent's remainder, idempotent per run+input;
  settings.pi.subagents {enabled, maxConcurrent, maxDepth} (subagentsEnabled kept as alias)
- child runs claim a concurrency slot under an advisory lock (waitForFact while
  queued); agent.await polls business tables without calling the model
- parent abort cascades to all descendants; parent runtime budget counts
  descendant usage; child events mirrored into the parent stream by parent seq
- authorize caps every child call by all ancestors' allowlists/kinds
- session page shows parent link, inherited info and the subagent tree
- e2e E11; runbook section on subagents

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/contracts/test/agent-events.test.ts

@@ -22,10 +22,28 @@ const samples: C.AgentRunEventBody[] = [
   { type: "compaction", phase: "end", reason: "threshold", status: "completed" },
   { type: "run_completed", finalText: "done", usage },
   { type: "run_failed", reason: "budget", message: "超预算", usage, budget: "tokens" },
+  {
+    type: "subagent_spawned",
+    childRunId: RUN,
+    goal: "子目标",
+    mode: "plan_only",
+    depth: 1,
+    capabilities: ["inventory.query"],
+    budget: { maxToolCalls: 5 },
+  },
+  {
+    type: "subagent_event",
+    childRunId: RUN,
+    childSeq: 3,
+    childType: "tool_call_end",
+    capabilityId: "inventory.query",
+    summary: "{}",
+  },
+  { type: "subagent_completed", childRunId: RUN, status: "succeeded", summary: "ok", usage, toolCalls: 1 },
 ];
 
 describe("agent 运行事件", () => {
-  it("样例覆盖全部 9 种事件类型", () => {
+  it("样例覆盖全部 12 种事件类型", () => {
     expect(samples.map((s) => s.type).sort()).toEqual([...C.AgentRunEventType.options].sort());
   });
 
@@ -60,6 +78,9 @@ describe("agent 运行事件", () => {
       null,
       "agent.run_status:succeeded",
       "agent.run_status:budget_exceeded",
+      "agent.tool_call:started",
+      "agent.tool_call:started",
+      "agent.tool_call:succeeded",
     ]);
     for (const b of bus) if (b) expect(C.parseEventPayload(b.type, b.payload), b.type).not.toBeNull();
   });