feat(client): surface subagent activity in sidebar

packages/client/runtime/src/client/index.ts

@@ -15,6 +15,8 @@ export { SlotsService } from './slots.ts'
 export type { RootOwnerProps } from './slots.ts'
 export { SessionCreateError, SessionsService, scopeOf, workspaceTitleOf } from './sessions/service.ts'
 export { SessionHistoryService } from './session-history/service.ts'
+export { indexSubagentDescendants } from './sessions/subagent-lineage.ts'
+export type { SubagentDescendantSummary } from './sessions/subagent-lineage.ts'
 // The provide channel is shared with the client test runtime (one
 // materialization/projection implementation; no test-side mirror to drift).
 export { SessionProvideChannel } from './sessions/provide.ts'

packages/client/runtime/src/client/sessions/subagent-lineage.ts

@@ -0,0 +1,50 @@
+/**
+ * Pure subagent-lineage aggregation over the retained session-list mirror.
+ * Ordinary forks terminate propagation so each visible session owns only its
+ * uninterrupted subagent subtree.
+ * @module @deepseek-ai/dsh-client-runtime/client/sessions/subagent-lineage
+ */
+import type { SessionId } from '@deepseek-ai/dsh-client-connection/client'
+import type { SessionSummary } from './service.ts'
+
+/** Descendant counts projected for one possible parent session. */
+export interface SubagentDescendantSummary {
+  /** All descendants connected through uninterrupted subagent-origin lineage. */
+  readonly count: number
+  /** Descendants whose exact session summary is currently running. */
+  readonly runningCount: number
+}
+
+/**
+ * Index every subagent descendant under each ancestor it reaches through an
+ * uninterrupted subagent-origin chain. Cycles fail soft and orphan owners
+ * remain harmless map keys until their summaries arrive.
+ * @param summaries - retained session summaries keyed by id.
+ * @returns descendant totals and running totals keyed by possible parent id.
+ */
+export function indexSubagentDescendants(
+  summaries: Readonly<Record<SessionId, SessionSummary>>,
+): ReadonlyMap<SessionId, SubagentDescendantSummary> {
+  const indexed = new Map<SessionId, { count: number; runningCount: number }>()
+  for (const descendant of Object.values(summaries)) {
+    if (descendant.origin !== 'subagent') continue
+    const seen = new Set<SessionId>()
+    let current: SessionSummary | undefined = descendant
+    while (current?.origin === 'subagent' && current.parentId !== undefined
+      && !seen.has(current.id)) {
+      seen.add(current.id)
+      const aggregate = indexed.get(current.parentId)
+      if (aggregate === undefined) {
+        indexed.set(current.parentId, {
+          count: 1,
+          runningCount: descendant.running ? 1 : 0,
+        })
+      } else {
+        aggregate.count += 1
+        if (descendant.running) aggregate.runningCount += 1
+      }
+      current = summaries[current.parentId]
+    }
+  }
+  return indexed
+}