Embedded.customJavac() only extracts Unix bash scripts (custom-javac.sh / java-forwarder.sh), breaking MavenBuildTool on Windows #1068

MavenBuildTool instruments Maven builds by extracting a wrapper javac via Embedded.customJavac(...) and passing -Dmaven.compiler.executable=${javac.executable} and -Dmaven.compiler.fork=true to Maven.

On Windows, even after working around #991 (mvnw.cmd / mvn.cmd resolution in MavenBuildTool.kt), Maven compilation immediately fails when maven-compiler-plugin tries to fork the compiler, because Embedded.customJavac() unconditionally extracts POSIX bash scripts (scip-java/custom-javac.sh and scip-java/java-forwarder.sh) to bin/javac and bin/java and calls Files.setPosixFilePermissions(...).

Affected Code (main)

• scip-java/src/main/kotlin/org/scip_code/scip_java/Embedded.kt (lines 32–56):

  fun customJavac(sourceroot: Path, targetroot: Path, tmp: Path): CustomJavac {
      val bin = tmp.resolve("bin")
      val javac = bin.resolve("javac")
      val java = bin.resolve("java")
      val agentJar = copyJar(tmp, "scip-java/scip-agent.jar")
      val pluginJar = copyJar(tmp, "scip-java/scip-javac.jar")
      copyResource(java, "scip-java/java-forwarder.sh")
      copyResource(javac, "scip-java/custom-javac.sh")
      Files.write(
          bin.resolve(".scip-Env"),
          """
          AGENT_JAR=$agentJar
          PLUGIN_JAR=$pluginJar
          SOURCEROOT=$sourceroot
          TARGETROOT=$targetroot
          JAVA_PATH=$java
          """.trimIndent().toByteArray(StandardCharsets.UTF_8),
      )
      val permissions = PosixFilePermissions.fromString("rwxr-xr-x")
      Files.setPosixFilePermissions(javac, permissions)
      Files.setPosixFilePermissions(java, permissions)
      return CustomJavac(javac, pluginJar)
  }

• scip-java/src/main/kotlin/org/scip_code/scip_java/buildtools/MavenBuildTool.kt (lines 27–43):

  val javac =
      Embedded.customJavac(
          index.workingDirectory,
          index.finalTargetroot(defaultTargetroot),
          tmp,
      )
  ...
  command += "-Dmaven.compiler.executable=${javac.executable}"
  command += "-Dmaven.compiler.fork=true"

Failure Modes on Windows

1. Files.setPosixFilePermissions(javac, permissions) in Embedded.customJavac() throws java.lang.UnsupportedOperationException on Windows NTFS filesystems because DefaultFileSystemProvider does not support the posix file attribute view.
2. -Dmaven.compiler.executable=<tmp>\bin\javac points to an extensionless #!/usr/bin/env bash script (custom-javac.sh). When maven-compiler-plugin forks the compiler on Windows via CreateProcess, it fails with:

   CreateProcess error=193, %1 is not a valid Win32 application
   

Suggested Fix

1. Guard Files.setPosixFilePermissions(...) behind FileSystems.getDefault().supportedFileAttributeViews().contains("posix") (similar to PR Fix ScipWriter temp file creation on file systems without POSIX permissions #1049).
2. On Windows (System.getProperty("os.name").lowercase().contains("win")), generate .cmd wrapper scripts (javac.cmd and java.cmd) in Embedded.customJavac(...) that invoke InjectScipOptions and forward to javac.exe / java.exe, and return bin.resolve("javac.cmd") as CustomJavac.executable.