fix(desktop): pin Compose packaging javaHome to the JBR toolchain (#6213)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/reusable-check.yml

@@ -546,7 +546,10 @@ jobs:
           install_jetbrains_jdk: 'true'
 
       - name: Build Desktop
-        run: ./gradlew :desktopApp:createDistributable -Pci=true
+        # proguardReleaseJars is included because it is otherwise only exercised by the
+        # release workflow: jlink tolerates a jmods-less JDK (JEP 493) but ProGuard does
+        # not, so a broken packaging JDK would surface at release time instead of here.
+        run: ./gradlew :desktopApp:createDistributable :desktopApp:proguardReleaseJars -Pci=true
 
       - name: Upload Desktop artifact
         if: ${{ inputs.upload_artifacts }}

desktopApp/build.gradle.kts

@@ -109,6 +109,24 @@ compose.desktop {
     application {
         mainClass = "org.meshtastic.desktop.MainKt"
 
+        // CMP resolves javaHome from the JVM running Gradle, not the Kotlin toolchain. On CI
+        // that's Temurin 25, which ships without jmods (JEP 493): jlink still works, but the
+        // ProGuard task derives -libraryjars from $javaHome/jmods and fails with ~857k
+        // unresolved java.* references. Pin packaging to the JBR SDK toolchain (jmods
+        // included) so ProGuard sees the platform classes and the bundled runtime is
+        // deterministically JBR 25 on every machine.
+        javaHome =
+            javaToolchains
+                .launcherFor {
+                    languageVersion.set(JavaLanguageVersion.of(25))
+                    vendor.set(JvmVendorSpec.JETBRAINS)
+                }
+                .get()
+                .metadata
+                .installationPath
+                .asFile
+                .absolutePath
+
         val desktopJvmArgs =
             listOf(
                 "-Xmx2G",