feat(pi): add subagent tracer bullet

modules/agents/pi/extensions/subagents/status.ts

@@ -0,0 +1,38 @@
+import type { ChildRecord, SpawnAccepted, SubagentResult, SubagentStatus } from "./types.ts";
+
+export function toAccepted(status: SubagentStatus): SpawnAccepted {
+  return {
+    id: status.id,
+    label: status.label,
+    context: status.context,
+    tools: status.tools,
+    state: status.state,
+    hint: `Use subagent_status or subagent_result with id ${status.id}`,
+  };
+}
+
+export function cloneStatus(status: SubagentStatus): SubagentStatus {
+  return { ...status, elapsedMs: elapsedMs(status) };
+}
+
+export function cloneResult(record: ChildRecord): SubagentResult {
+  const status = cloneStatus(record.status);
+  const terminal = ["completed", "failed", "cancelled", "timed_out", "orphaned"].includes(status.state);
+  return {
+    id: status.id,
+    state: status.state,
+    running: !terminal,
+    resultAvailable: status.resultAvailable,
+    result: record.result,
+    error: status.error,
+    completedAt: status.completedAt,
+    elapsedMs: status.elapsedMs,
+  };
+}
+
+export function elapsedMs(status: Pick<SubagentStatus, "startedAt" | "completedAt">): number {
+  const start = Date.parse(status.startedAt);
+  const end = status.completedAt ? Date.parse(status.completedAt) : Date.now();
+  if (!Number.isFinite(start) || !Number.isFinite(end)) return 0;
+  return Math.max(0, end - start);
+}