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/coding-agent/src/cli/initial-message.ts

@@ -0,0 +1,43 @@
+import type { ImageContent } from "@earendil-works/pi-ai";
+import type { Args } from "./args.ts";
+
+export interface InitialMessageInput {
+	parsed: Args;
+	fileText?: string;
+	fileImages?: ImageContent[];
+	stdinContent?: string;
+}
+
+export interface InitialMessageResult {
+	initialMessage?: string;
+	initialImages?: ImageContent[];
+}
+
+/**
+ * Combine stdin content, @file text, and the first CLI message into a single
+ * initial prompt for non-interactive mode.
+ */
+export function buildInitialMessage({
+	parsed,
+	fileText,
+	fileImages,
+	stdinContent,
+}: InitialMessageInput): InitialMessageResult {
+	const parts: string[] = [];
+	if (stdinContent !== undefined) {
+		parts.push(stdinContent);
+	}
+	if (fileText) {
+		parts.push(fileText);
+	}
+
+	if (parsed.messages.length > 0) {
+		parts.push(parsed.messages[0]);
+		parsed.messages.shift();
+	}
+
+	return {
+		initialMessage: parts.length > 0 ? parts.join("") : undefined,
+		initialImages: fileImages && fileImages.length > 0 ? fileImages : undefined,
+	};
+}