feat(ai): add shared contentText utility (#6840)

Co-authored-by: Armin Ronacher <armin.ronacher@active-4.com>

packages/agent/src/harness/agent-harness.ts

@@ -1,4 +1,11 @@
-import type { AssistantMessage, ImageContent, Model, Models, UserMessage } from "@earendil-works/pi-ai";
+import {
+	type AssistantMessage,
+	contentText,
+	type ImageContent,
+	type Model,
+	type Models,
+	type UserMessage,
+} from "@earendil-works/pi-ai";
 import { runAgentLoop } from "../agent-loop.ts";
 import type {
 	AgentContext,
@@ -781,23 +788,10 @@ export class AgentHarness<
 			let newLeafId: string | null;
 			if (targetEntry.type === "message" && targetEntry.message.role === "user") {
 				newLeafId = targetEntry.parentId;
-				const content = targetEntry.message.content;
-				editorText =
-					typeof content === "string"
-						? content
-						: content
-								.filter((c): c is { readonly type: "text"; readonly text: string } => c.type === "text")
-								.map((c) => c.text)
-								.join("");
+				editorText = contentText(targetEntry.message.content, "");
 			} else if (targetEntry.type === "custom_message") {
 				newLeafId = targetEntry.parentId;
-				editorText =
-					typeof targetEntry.content === "string"
-						? targetEntry.content
-						: targetEntry.content
-								.filter((c): c is { readonly type: "text"; readonly text: string } => c.type === "text")
-								.map((c) => c.text)
-								.join("");
+				editorText = contentText(targetEntry.content, "");
 			} else {
 				newLeafId = targetId;
 			}