test(provider): reproduce cache breakpoint landing on ephemeral tail

Author: TheGreatAxios

src/provider/anthropic-cache-breakpoint.test.ts

@@ -0,0 +1,59 @@
+import { describe, expect, test } from "bun:test";
+import { createAnthropicAdapter } from "@intx/inference/providers";
+import type {
+  ConversationTurn,
+  InferenceOptions,
+} from "@intx/types/runtime";
+
+const source = {
+  sourceId: "test-anthropic",
+  provider: "anthropic",
+  model: "test-anthropic-model",
+};
+
+function userTurn(text: string): ConversationTurn {
+  return {
+    role: "user",
+    timestamp: 0,
+    content: [{ type: "text", text }],
+  };
+}
+
+function assistantTurn(text: string): ConversationTurn {
+  return {
+    role: "assistant",
+    timestamp: 0,
+    content: [{ type: "text", text }],
+  };
+}
+
+type WireMessage = {
+  role: string;
+  content: { cache_control?: unknown; text?: string }[];
+};
+
+function wireMessages(body: string): WireMessage[] {
+  return (JSON.parse(body) as { messages: WireMessage[] }).messages;
+}
+
+describe("anthropic cache breakpoint with ephemeral turns", () => {
+  test("breakpoint lands on the last persisted user turn, not the ephemeral tail", () => {
+    const persisted = [userTurn("q1"), assistantTurn("a1"), userTurn("q2")];
+    const nudge = userTurn("wrap up soon");
+    const request = createAnthropicAdapter(source).buildRequest(
+      [...persisted, nudge],
+      "test-anthropic-model",
+      { ephemeralTurns: [nudge] } as InferenceOptions,
+    );
+    const messages = wireMessages(request.body);
+
+    expect(messages).toHaveLength(4);
+    expect(messages[3]?.content[0]?.text).toBe("wrap up soon");
+    expect(
+      messages[2]?.content[messages[2].content.length - 1]?.cache_control,
+    ).toEqual({ type: "ephemeral" });
+    expect(
+      messages[3]?.content.filter((block) => block.cache_control !== undefined),
+    ).toEqual([]);
+  });
+});