chore(vendor): import pi 0.85.1

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

third_party/pi/packages/ai/src/utils/text.ts

@@ -0,0 +1,12 @@
+import type { ImageContent, TextContent, ThinkingContent, ToolCall } from "../types.ts";
+
+type Content = TextContent | ImageContent | ThinkingContent | ToolCall;
+
+/** Extract and join text from message content. */
+export function contentText(content: string | readonly Content[], separator = "\n"): string {
+	if (typeof content === "string") return content;
+	return content
+		.filter((block) => block.type === "text")
+		.map((block) => block.text)
+		.join(separator);
+}