feat(acp): add experimental ACP support

Co-authored-by: Jonathan Taylor <visionik@pobox.com>

src/acp/event-mapper.test.ts

@@ -0,0 +1,34 @@
+import { describe, expect, it } from "vitest";
+
+import { extractAttachmentsFromPrompt, extractTextFromPrompt } from "./event-mapper.js";
+
+describe("acp event mapper", () => {
+  it("extracts text and resource blocks into prompt text", () => {
+    const text = extractTextFromPrompt([
+      { type: "text", text: "Hello" },
+      { type: "resource", resource: { text: "File contents" } },
+      { type: "resource_link", uri: "https://example.com", title: "Spec" },
+      { type: "image", data: "abc", mimeType: "image/png" },
+    ]);
+
+    expect(text).toBe(
+      "Hello\nFile contents\n[Resource link (Spec)] https://example.com",
+    );
+  });
+
+  it("extracts image blocks into gateway attachments", () => {
+    const attachments = extractAttachmentsFromPrompt([
+      { type: "image", data: "abc", mimeType: "image/png" },
+      { type: "image", data: "", mimeType: "image/png" },
+      { type: "text", text: "ignored" },
+    ]);
+
+    expect(attachments).toEqual([
+      {
+        type: "image",
+        mimeType: "image/png",
+        content: "abc",
+      },
+    ]);
+  });
+});