desktop: escape the attribute values interpolated into the MSIX fragments

before-build.mjs builds the msix-extensions.xml fragment and the hidden
CLI <Application> entries from string templates, interpolating the
display name and the payload-declared launcher stems raw. A value with
`&`, `<` or `"` would corrupt the manifest makeappx reads (an opaque
0x80080204 at best, a differently named alias at worst). Every
interpolated attribute now goes through xmlAttribute().

apps/desktop/scripts/before-build.mjs

@@ -101,8 +101,8 @@ function writeMsixExtensions() {
   <uap3:AppExtension
       Name="com.microsoft.windows.copilotkeyprovider"
       Id="CopilotKeyProvider"
-      DisplayName="${displayName}"
-      Description="Launch ${displayName} with the Copilot key"
+      DisplayName="${xmlAttribute(displayName)}"
+      Description="Launch ${xmlAttribute(displayName)} with the Copilot key"
       PublicFolder="Public">
     <uap3:Properties>
       <SingleTap>hermes://copilot-key/start?state=Tap</SingleTap>
@@ -117,6 +117,15 @@ ${aliases}`
   fs.writeFileSync(file, copilot)
 }
 
+// The manifest fragments above are string templates; a display name or a
+// payload-declared launcher stem carrying `&`, `<` or `"` would otherwise
+// corrupt the XML makeappx reads (an opaque 0x80080204 at best, a different
+// alias at worst).
+/** @param {string} value */
+export function xmlAttribute(value) {
+  return String(value).replace(/[&<>"']/g, (c) => `&#${c.charCodeAt(0)};`)
+}
+
 /**
  * One uap5:Extension carries the aliases declared by the payload.
  * Exported pure for tests.
@@ -128,8 +137,8 @@ export function appExecutionAliasApplications(launchers, identity) {
   // Give each CLI its own hidden application, with one extension per app.
   return launchers.map((name, index) => {
     const executable = ['app', 'resources', 'agent-payload', 'bin', `${name}.exe`].join(String.fromCharCode(92))
-    return `<Application Id="${identity.appNamePascal}Cli${index}" Executable="${executable}" EntryPoint="Windows.FullTrustApplication">
-      <uap:VisualElements DisplayName="${identity.displayName}" Description="${identity.displayName} CLI"
+    return `<Application Id="${xmlAttribute(identity.appNamePascal)}Cli${index}" Executable="${xmlAttribute(executable)}" EntryPoint="Windows.FullTrustApplication">
+      <uap:VisualElements DisplayName="${xmlAttribute(identity.displayName)}" Description="${xmlAttribute(identity.displayName)} CLI"
         Square150x150Logo="assets\\Square150x150Logo.png" Square44x44Logo="assets\\Square44x44Logo.png"
         BackgroundColor="transparent" AppListEntry="none" />
       <Extensions>${appExecutionAliasExtensions([name])}</Extensions>
@@ -147,11 +156,11 @@ export function appExecutionAliasExtensions(launchers) {
   return `<uap5:Extension
     xmlns:uap5="http://schemas.microsoft.com/appx/manifest/uap/windows10/5"
     Category="windows.appExecutionAlias"
-    Executable="${executable(launchers[0])}"
+    Executable="${xmlAttribute(executable(launchers[0]))}"
     EntryPoint="Windows.FullTrustApplication">
   <uap5:AppExecutionAlias>
 ${launchers
-  .map((name) => `    <uap5:ExecutionAlias Alias="${name}.exe" />`)
+  .map((name) => `    <uap5:ExecutionAlias Alias="${xmlAttribute(name)}.exe" />`)
   .join('\n')}
   </uap5:AppExecutionAlias>
 </uap5:Extension>`

apps/desktop/scripts/cli-launchers.test.mjs

@@ -1,6 +1,6 @@
 import assert from 'node:assert/strict'
 import { test } from 'vitest'
-import { appExecutionAliasExtensions } from './before-build.mjs'
+import { appExecutionAliasApplications, appExecutionAliasExtensions, xmlAttribute } from './before-build.mjs'
 
 test('one MSIX extension consumes the launchers declared by the payload', () => {
   const names = ['custom-cli', 'another-cli']
@@ -12,3 +12,12 @@ test('one MSIX extension consumes the launchers declared by the payload', () =>
   assert.ok(!xml.includes('desktop6:Service'))
   assert.equal(appExecutionAliasExtensions([]), '')
 })
+
+test('manifest fragments escape every interpolated attribute value', () => {
+  const xml = appExecutionAliasApplications(['odd"&<name'], { appNamePascal: 'Hermes', displayName: 'Hermes & "Friends" <beta>' })
+  const values = [...xml.matchAll(/="([^"]*)"/g)].map((m) => m[1].replace(/&#\d+;/g, ''))
+  assert.ok(values.length > 0 && values.every((v) => !/[&<>"']/.test(v)), xml)
+  assert.ok(xml.includes('DisplayName="Hermes &#38; &#34;Friends&#34; &#60;beta&#62;"'))
+  assert.ok(xml.includes('Alias="odd&#34;&#38;&#60;name.exe"'))
+  assert.equal(xmlAttribute('plain-name'), 'plain-name')
+})