feat(sdk): chat.channel() and chat.session() for the current run's Session

Ergonomic accessors so a chat.agent run can open a named side channel on its
own Session without threading the session id: chat.channel(name) is a shortcut
for chat.session().channel(name).

Author: ericallam

packages/trigger-sdk/src/v3/ai.ts

@@ -107,6 +107,8 @@ type ToolCallOptions = {
 import { readFileInSkill, runBashInSkill } from "./agentSkillsRuntime.js";
 import { ensureAiSdkTelemetry } from "./aiAutoTelemetry.js";
 import {
+  type SessionChannelHandle,
+  type SessionChannelOptions,
   type SessionHandle,
   type SessionPipeStreamOptions,
   sessions,
@@ -11849,6 +11851,16 @@ export const chat = {
   response: chatResponse,
   /** Pre-built input stream for receiving messages from the transport. */
   messages: messagesInput,
+  /** The current chat.agent run's Session handle. See {@link SessionHandle}. */
+  session: getChatSession,
+  /**
+   * Open a named side channel on the current chat.agent run's Session: a
+   * durable, cross-run `.in`/`.out` pair addressed by `name`, separate from the
+   * chat transcript. Writing its `.in` does not wake a run. Shortcut for
+   * `chat.session().channel(name)`.
+   */
+  channel: (name: string, options?: SessionChannelOptions): SessionChannelHandle =>
+    getChatSession().channel(name, options),
   /** Create a managed stop signal wired to the stop input stream. See {@link createStopSignal}. */
   createStopSignal,
   /** Signal the frontend that the current turn is complete. See {@link chatWriteTurnComplete}. */