fix(desktop): harden external editor and session cookie IPC (#1627)

* fix(desktop): stop the renderer choosing the external editor binary or reading the session cookie

open-external-editor now launches only the editor saved from a file dialog
and refuses to hand executable file types to the OS opener. The unused
get-session-cookie and wait-session-cookie channels, which returned the
httpOnly jwt, are removed.

* fix: validate setting keys before editor authorization

scripts/electron-external-editor.test.ts

@@ -0,0 +1,40 @@
+import { createRequire } from "node:module";
+import { describe, expect, it } from "vitest";
+
+const require = createRequire(import.meta.url);
+const { isLaunchableFileName } = require("../electron/external-editor.cjs") as {
+  isLaunchableFileName: (fileName: unknown) => boolean;
+};
+
+describe("Electron external editor", () => {
+  it("refuses remote file names the OS would run instead of open", () => {
+    for (const name of [
+      "payload.exe",
+      "run.BAT",
+      "script.ps1",
+      "a.exe. ",
+      "a.cmd...",
+      "../../evil.vbs",
+      "start.command",
+      "launch.desktop",
+      "install.sh",
+    ]) {
+      expect(isLaunchableFileName(name)).toBe(true);
+    }
+  });
+
+  it("opens ordinary text files", () => {
+    for (const name of [
+      "nginx.conf",
+      "README.md",
+      "Dockerfile",
+      ".bashrc",
+      "config.json",
+      "index.ts",
+      "",
+      undefined,
+    ]) {
+      expect(isLaunchableFileName(name)).toBe(false);
+    }
+  });
+});