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/test/suite/regressions/8337-utf8-bom-parsing.test.ts

@@ -0,0 +1,49 @@
+import { existsSync, mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { SettingsManager } from "../../../src/core/settings-manager.ts";
+import { parseFrontmatter } from "../../../src/utils/frontmatter.ts";
+import { splitBom } from "../../../src/utils/text.ts";
+
+describe("issue #8337 UTF-8 BOM parsing", () => {
+	let testDir: string;
+
+	beforeEach(() => {
+		testDir = mkdtempSync(join(tmpdir(), "pi-8337-"));
+	});
+
+	afterEach(() => {
+		if (existsSync(testDir)) {
+			rmSync(testDir, { recursive: true, force: true });
+		}
+	});
+
+	it("loads frontmatter and settings with a leading BOM", async () => {
+		expect(splitBom("\uFEFFcontent")).toEqual({ bom: "\uFEFF", text: "content" });
+		const document = "---\nname: demo\ndescription: Test\n---\nBody";
+		expect(parseFrontmatter(`\uFEFF${document}`)).toEqual({
+			frontmatter: { name: "demo", description: "Test" },
+			body: "Body",
+		});
+
+		const agentDir = join(testDir, "agent");
+		const projectDir = join(testDir, "project");
+		mkdirSync(join(projectDir, ".pi"), { recursive: true });
+		mkdirSync(agentDir, { recursive: true });
+		const globalSettingsPath = join(agentDir, "settings.json");
+		writeFileSync(globalSettingsPath, `\uFEFF${JSON.stringify({ defaultModel: "global-model" })}`);
+		writeFileSync(
+			join(projectDir, ".pi", "settings.json"),
+			`\uFEFF${JSON.stringify({ defaultProvider: "project-provider" })}`,
+		);
+
+		const settings = SettingsManager.create(projectDir, agentDir);
+		expect(settings.getDefaultModel()).toBe("global-model");
+		expect(settings.getDefaultProvider()).toBe("project-provider");
+
+		settings.setTheme("dark");
+		await settings.flush();
+		expect(readFileSync(globalSettingsPath, "utf-8")).not.toMatch(/^\uFEFF/);
+	});
+});