Fix: handle DOS games in subdirectories inside .jsdos bundles

When a ZIP contains game files in a subdirectory (e.g. doomiido/),
findMainExe() correctly finds the executable but the bundle autoexec
was using just the filename, causing DOSBox 'Illegal command' error.

- Use extractDir.relativize() to compute the relative exe path
- buildDosboxConf() now adds 'cd dirname' before running the exe
- buildJsdosJson() uses 'cd dirname && exe' for multi-line script
- Fix applies to both sockdrive and standard bundle paths

src/main/java/com/dostalgia/UploadResource.java

@@ -88,7 +88,7 @@ public class UploadResource {
                 // Write dosbox.conf (full config, not just autoexec)
                 Path jsdos = gameDir.resolve(".jsdos");
                 Files.createDirectories(jsdos);
-                String relExe = Path.of(mainExe).getFileName().toString();
+                String relExe = extractDir.relativize(Path.of(mainExe)).toString().replace('\\', '/');
                 String conf = buildDosboxConf(relExe);
                 Files.writeString(jsdos.resolve("dosbox.conf"), conf);
                 Files.write(jsdos.resolve("jsdos.json"), buildJsdosJson(relExe));
@@ -216,7 +216,7 @@ public class UploadResource {
             // Create .jsdos config (full config, not just autoexec)
             Path jsdos = tmpBundle.resolve(".jsdos");
             Files.createDirectories(jsdos);
-            String relExe = Path.of(mainExe).getFileName().toString();
+            String relExe = extractDir.relativize(Path.of(mainExe)).toString().replace('\\', '/');
             String conf = buildDosboxConf(relExe);
             Files.writeString(jsdos.resolve("dosbox.conf"), conf);
             Files.write(jsdos.resolve("jsdos.json"), buildJsdosJson(relExe));
@@ -247,9 +247,18 @@ public class UploadResource {
      * translate physical key presses into game input.
      */
     private byte[] buildJsdosJson(String relExe) {
+        // Split into directory and executable components for subdirectory support
+        String dir = "";
+        String exe = relExe;
+        int idx = relExe.lastIndexOf('/');
+        if (idx >= 0) {
+            dir = relExe.substring(0, idx);
+            exe = relExe.substring(idx + 1);
+        }
+        String script = (dir.isEmpty() ? "" : "cd " + dir + " && ") + exe;
         String json = "{"
             + "\"autoexec\":{"
-            + "\"options\":{\"script\":{\"value\":\"" + escapeJson(relExe) + "\"}}"
+            + "\"options\":{\"script\":{\"value\":\"" + escapeJson(script) + "\"}}"
             + "},"
             + "\"output\":{"
             + "\"options\":{\"autolock\":{\"value\":true}}}"
@@ -262,6 +271,15 @@ public class UploadResource {
     }
 
     private String buildDosboxConf(String relExe) {
+        // Split into directory and executable components for subdirectory support
+        String dir = "";
+        String exe = relExe;
+        int idx = relExe.lastIndexOf('/');
+        if (idx >= 0) {
+            dir = relExe.substring(0, idx);
+            exe = relExe.substring(idx + 1);
+        }
+
         return "[sdl]\n"
             + "autolock=true\n"
             + "usescancodes=true\n"
@@ -291,7 +309,8 @@ public class UploadResource {
             + "mount c .\n"
             + "c:\n"
             + "cls\n"
-            + relExe + "\n";
+            + (dir.isEmpty() ? "" : "cd " + dir + "\n")
+            + exe + "\n";
     }
 
     /**