Surface WiX tool stdout/stderr on MSI build failure

scripts/guibuild.py

@@ -233,9 +233,17 @@ def build_msi(version: str) -> Path:
     def run(tool: str, args: list[str]) -> None:
         cmd = [str(wix / tool), *args]
         print(f"Running: {' '.join(cmd)}")
-        result = subprocess.run(cmd, cwd=_REPO_ROOT)
+        try:
+            result = subprocess.run(
+                cmd, cwd=_REPO_ROOT, capture_output=True, text=True
+            )
+        except OSError as exc:
+            raise RuntimeError(f"{tool} failed to start: {exc}") from exc
         if result.returncode != 0:
-            raise RuntimeError(f"{tool} failed with exit code {result.returncode}")
+            raise RuntimeError(
+                f"{tool} failed with exit code {result.returncode}\n"
+                f"stdout:\n{result.stdout}\nstderr:\n{result.stderr}"
+            )
 
     run("heat.exe", [
         "dir", str(dist_folder),