feat(web): add subagent conversation transport

packages/host/apiproxy/src/api/subagents.ts

@@ -0,0 +1,72 @@
+/**
+ * Browser-safe subagent domain contract. Persisted transcript reads never
+ * activate an Agent, while prompts route through the direct parent's
+ * Activation-backed continuation owner.
+ */
+
+import type { MessageId } from '@deepseek-ai/dsh-llm/brand'
+import type { ContentBlock } from '@deepseek-ai/dsh-llm/types'
+import type { SessionId } from '@deepseek-ai/dsh-session/types'
+import type { RpcRequest, RpcResponse } from './rpc.ts'
+import type { HistoryEntry } from './sessions.ts'
+
+/** Complete durable direct-child catalog row. */
+export type SubagentListEntry =
+  | {
+    kind: 'child'
+    id: SessionId
+    label: string
+    activity: 'running' | 'inactive'
+  }
+  | {
+    kind: 'diagnostic'
+    id: SessionId
+    reason: 'corrupt' | 'unsupported' | 'unavailable'
+  }
+
+/** Inbox identity returned once the continuation accepts one human message. */
+export interface SubagentPromptReceipt {
+  messageId: MessageId
+}
+
+/** Durable parent/child address that selects subagent transport in the client. */
+export interface SubagentAddress {
+  parentSessionId: SessionId
+  childSessionId: SessionId
+}
+
+/** Complete direct-child catalog plus the delivery-time parent availability hint. */
+export interface SubagentCatalog {
+  entries: SubagentListEntry[]
+  parentAvailable: boolean
+}
+
+/** Subagent-domain unary methods. */
+export interface SubagentsApi {
+  /**
+   * Lists direct continuable children without loading either side. Parent
+   * availability is a hint; prompt performs the authoritative check.
+   */
+  list(
+    request: RpcRequest<{ parentSessionId: SessionId }>,
+    signal?: AbortSignal,
+  ): Promise<RpcResponse<SubagentCatalog>>
+
+  /**
+   * Reads one healthy catalog child's persisted raw log with ordinary
+   * message-aligned pagination and render intents, without Agent activation.
+   */
+  history(
+    request: RpcRequest<SubagentAddress & { beforeSeq?: number; maxMessages?: number }>,
+    signal?: AbortSignal,
+  ): Promise<RpcResponse<{ events: HistoryEntry[]; hasMore: boolean }>>
+
+  /**
+   * Delivers human content through the exact live parent's continuation
+   * owner. Success identifies the accepted inbox message.
+   */
+  prompt(
+    request: RpcRequest<SubagentAddress & { content: ContentBlock[] }>,
+    signal?: AbortSignal,
+  ): Promise<RpcResponse<SubagentPromptReceipt>>
+}