Load config.json saved with a UTF-8 byte order mark (#5315)

* Load config.json saved with a UTF-8 byte order mark

Windows Notepad saves UTF-8 with a BOM. Both config readers passed the
text straight to JSON.parse, so the daemon refused to start and CLI
config commands failed with "Unexpected token".

Closes #4683

* Strip the config BOM with an anchored replace

---------

Co-authored-by: paseo-bot[bot] <266920839+paseo-bot[bot]@users.noreply.github.com>

packages/server/src/server/persisted-config.test.ts

@@ -6,6 +6,7 @@ import { describe, expect, test } from "vitest";
 import {
   loadPersistedConfig,
   PersistedConfigSchema,
+  readPersistedConfig,
   savePersistedConfig,
 } from "./persisted-config.js";
 import { PRIVATE_DIRECTORY_MODE, PRIVATE_FILE_MODE } from "./private-files.js";
@@ -736,6 +737,34 @@ describe("loadPersistedConfig", () => {
   });
 });
 
+describe("config.json saved with a UTF-8 byte order mark", () => {
+  // Windows Notepad writes this shape: a BOM, then CRLF line endings.
+  const notepadConfig =
+    '{\r\n  "version": 1,\r\n  "daemon": { "listen": "127.0.0.1:6767" }\r\n}\r\n';
+
+  test("loadPersistedConfig reads it", () => {
+    const home = createTempHome();
+    try {
+      writeFileSync(path.join(home, "config.json"), notepadConfig);
+
+      expect(loadPersistedConfig(home).daemon?.listen).toBe("127.0.0.1:6767");
+    } finally {
+      rmSync(home, { recursive: true, force: true });
+    }
+  });
+
+  test("readPersistedConfig reads it", () => {
+    const home = createTempHome();
+    try {
+      writeFileSync(path.join(home, "config.json"), notepadConfig);
+
+      expect(readPersistedConfig(home).daemon?.listen).toBe("127.0.0.1:6767");
+    } finally {
+      rmSync(home, { recursive: true, force: true });
+    }
+  });
+});
+
 describe.skipIf(process.platform === "win32")("persisted config file permissions", () => {
   test("initializes config.json with private permissions", () => {
     const home = createTempHome();

packages/server/src/server/persisted-config.ts

@@ -438,7 +438,7 @@ export function loadPersistedConfig(paseoHome: string, logger?: LoggerLike): Per
 
   let parsed: unknown;
   try {
-    parsed = JSON.parse(raw);
+    parsed = parseConfigText(raw);
   } catch (err) {
     const message = err instanceof Error ? err.message : String(err);
     throw new Error(`[Config] Invalid JSON in ${configPath}: ${message}`, {
@@ -472,7 +472,14 @@ export function readPersistedConfig(
       return options.defaultsIfMissing ? structuredClone(DEFAULT_PERSISTED_CONFIG) : {};
     throw error;
   }
-  return PersistedConfigSchema.parse(stripRemovedConfigFields(JSON.parse(raw))) as PersistedConfig;
+  return PersistedConfigSchema.parse(
+    stripRemovedConfigFields(parseConfigText(raw)),
+  ) as PersistedConfig;
+}
+
+/** Editors such as Windows Notepad save UTF-8 with a byte order mark, which JSON.parse rejects. */
+function parseConfigText(raw: string): unknown {
+  return JSON.parse(raw.replace(/^\uFEFF/, ""));
 }
 
 function configPathParts(field: string): string[] {