Squashed 'src/pi/' content from commit d981de122

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

packages/coding-agent/test/suite/regressions/7911-json-stream-usage.test.ts

@@ -0,0 +1,32 @@
+import { fauxAssistantMessage } from "@earendil-works/pi-ai";
+import { afterEach, describe, expect, it } from "vitest";
+import { toJsonEvent } from "../../../src/modes/json-event.ts";
+import { createHarness, type Harness } from "../harness.ts";
+
+describe("regression #7911: JSON message updates retain usage", () => {
+	let harness: Harness | undefined;
+
+	afterEach(() => {
+		harness?.cleanup();
+	});
+
+	it("includes cumulative usage without cumulative message snapshots", async () => {
+		harness = await createHarness();
+		harness.setResponses([fauxAssistantMessage("hello")]);
+
+		await harness.session.prompt("respond");
+
+		// #7290's delta-only wire projection dropped this fixed-size metadata with the snapshots.
+		const update = harness
+			.eventsOfType("message_update")
+			.find((event) => event.message.role === "assistant" && event.message.usage.totalTokens > 0);
+		if (!update || update.message.role !== "assistant") {
+			throw new Error("Expected an assistant update with populated usage");
+		}
+
+		const wireUpdate = toJsonEvent(update);
+		expect(wireUpdate.usage).toEqual(update.message.usage);
+		expect(wireUpdate).not.toHaveProperty("message");
+		expect(wireUpdate.assistantMessageEvent).not.toHaveProperty("partial");
+	});
+});