Squashed 'third_party/pi/' content from commit d981de122

git-subtree-dir: third_party/pi
git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

packages/ai/test/anthropic-thinking-binding-e2e.test.ts

@@ -0,0 +1,59 @@
+import { describe, expect, it } from "vitest";
+import { stream } from "../src/api/anthropic-messages.ts";
+import { getModel } from "../src/compat.ts";
+import type { AssistantMessage, Context } from "../src/types.ts";
+
+const enabled = Boolean(process.env.ANTHROPIC_API_KEY);
+const model = getModel("anthropic", "claude-fable-5-1");
+const user = (content: string, timestamp: number) => ({ role: "user" as const, content, timestamp });
+
+function strictBinding(payload: unknown): unknown {
+	const params = payload as {
+		thinking?: {
+			block_binding?: { prefix_mismatch_behavior?: "drop_block" | "error" };
+		};
+	};
+	if (params.thinking?.block_binding) {
+		params.thinking.block_binding.prefix_mismatch_behavior = "error";
+	}
+	return params;
+}
+
+async function request(context: Context, effort: "low" | "high"): Promise<AssistantMessage> {
+	return stream(model, context, {
+		apiKey: process.env.ANTHROPIC_API_KEY,
+		cacheRetention: "none",
+		maxTokens: 1536,
+		thinkingEnabled: true,
+		thinkingDisplay: "summarized",
+		effort,
+		onPayload: strictBinding,
+	}).result();
+}
+
+describe.skipIf(!enabled)("Anthropic thinking binding conformance", () => {
+	it("replays managed effort markers required by signed Fable thinking", { timeout: 120000 }, async () => {
+		const firstUser = user("Compute 982451653 multiplied by 961748941. Return only the integer.", 1);
+		const first = await request({ messages: [firstUser] }, "low");
+		expect(first.stopReason, first.errorMessage).toBe("stop");
+		expect(
+			first.content.some(
+				(block) =>
+					block.type === "thinking" &&
+					typeof block.thinkingSignature === "string" &&
+					block.thinkingSignature.length > 0,
+			),
+		).toBe(true);
+		expect(first.providerThinkingLevel).toBe("low");
+
+		const secondUser = user("Reply with exactly: ok", 2);
+		const exact = await request({ messages: [firstUser, first, secondUser] }, "high");
+		expect(exact.stopReason, exact.errorMessage).toBe("stop");
+
+		const unmanagedHistory: AssistantMessage = { ...first };
+		delete unmanagedHistory.providerThinkingLevel;
+		const missingMarker = await request({ messages: [firstUser, unmanagedHistory, secondUser] }, "high");
+		expect(missingMarker.stopReason).toBe("error");
+		expect(missingMarker.errorMessage).toContain("Invalid `signature`");
+	});
+});