Add logging for implicit Wasm behaviors; rebase on upstream main

- Log when --experimental-wasm-exnref is injected in runJs (Node.js < 25)
- Log when Wasm mode enables ES module output in Run.scala
- Improve comment in Wasm.scala directive to reference AmbiguousPlatformError
  for --wasm + --platform native conflict detection

Author: lostflydev

modules/build/src/main/scala/scala/build/internal/Runner.scala

@@ -283,6 +283,10 @@ object Runner {
         .map(_.toString)
         .toRight(NodeNotFoundError()))
     val nodeFlags = if (emitWasm && nodeNeedsWasmFlag) List("--experimental-wasm-exnref") else Nil
+    if (emitWasm && nodeFlags.nonEmpty)
+      logger.log(
+        s"Wasm: adding ${nodeFlags.mkString(" ")} (required for Wasm exception handling on Node.js < 25)"
+      )
     if !jsDom && allowExecve && Execve.available() then {
       val command = Seq(nodePath) ++ nodeFlags ++ Seq(entrypoint.getAbsolutePath) ++ args
 

modules/cli/src/main/scala/scala/cli/commands/run/Run.scala

@@ -480,6 +480,7 @@ object Run extends ScalaCommand[RunOptions] with BuildCommandHelpers {
           if jsOpts.jsEmitWasm then {
             val runtime  = jsOpts.wasmRuntime
             val esModule = true // Wasm backend uses ES modules
+            logger.log("Wasm mode enabled: using ES module output on JS platform")
             scratchDirOpt.foreach(os.makeDir.all(_))
             val jsDest = os.temp(
               dir = scratchDirOpt.orNull,

modules/directives/src/main/scala/scala/build/preprocessing/directives/Wasm.scala

@@ -37,7 +37,8 @@ final case class Wasm(
       }
     parsedRuntime.map { runtime =>
       val wasmEnabled = wasm.getOrElse(false) || wasmRuntime.isDefined
-      // When Wasm is enabled, force Platform.JS (Scala.js Wasm backend requires JS compilation)
+      // Scala.js Wasm backend requires JS platform. When --platform native is also
+      // specified alongside --wasm, an AmbiguousPlatformError is raised in platform resolution.
       val scalaOptions =
         if (wasmEnabled)
           ScalaOptions(platform = Some(Positioned.none(Platform.JS)))