Add executable picker in game edit UI

- Added 'executables' (full list) and 'executable' (selected) fields to Game
- Upload now stores ALL discoverable .exe/.com/.bat files in game metadata
- Added setExecutable() to GameService that patches the .jsdos bundle
  (updates dosbox.conf + jsdos.json inside the ZIP) when changing executable
- GameResource PATCH handler delegates executable changes to bundle patching
- GameDetail edit mode shows a radio-button picker of all executables
- Heuristics remain as first-guess default, user can always override
- No re-upload needed to fix wrong executable selection

frontend/src/pages/GameDetail.svelte

@@ -17,6 +17,7 @@
   let editPublisher = $state("");
   let editDescription = $state("");
   let editPlatform = $state("");
+  let editExecutable = $state("");
 
   // IGDB scrape state
   let scraping = $state(false);
@@ -65,6 +66,7 @@
     editPublisher = game.publisher || "";
     editDescription = game.description || "";
     editPlatform = game.platform || "";
+    editExecutable = game.executable || "";
     editing = true;
   }
 
@@ -79,6 +81,7 @@
         publisher: editPublisher || undefined,
         description: editDescription || undefined,
         platform: editPlatform || undefined,
+        executable: editExecutable || undefined,
       });
       editing = false;
     } catch (e) {
@@ -207,6 +210,25 @@
               <option value="windows">Windows</option>
             </select>
           </div>
+          {#if game.executables && game.executables.length > 0}
+            <div class="edit-exec-section">
+              <span class="edit-exec-label">Main executable:</span>
+              <div class="edit-exec-list">
+                {#each game.executables as exe}
+                  <label class="edit-exec-option" class:selected={editExecutable === exe}>
+                    <input
+                      type="radio"
+                      name="executable"
+                      value={exe}
+                      checked={editExecutable === exe}
+                      onchange={() => editExecutable = exe}
+                    />
+                    <span class="edit-exec-path">{exe}</span>
+                  </label>
+                {/each}
+              </div>
+            </div>
+          {/if}
           <div class="edit-actions">
             <button class="btn btn-primary" onclick={saveEdit} disabled={saving}>
               {saving ? "Saving..." : "Save"}
@@ -601,6 +623,62 @@
     color: #66ff66;
   }
 
+  /* ─── Executable Picker ────────────────────── */
+  .edit-exec-section {
+    margin-top: 12px;
+    padding-top: 12px;
+    border-top: 1px solid var(--border);
+  }
+  .edit-exec-label {
+    display: block;
+    font-size: 0.8rem;
+    color: var(--text-dim);
+    font-weight: 600;
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+    margin-bottom: 8px;
+  }
+  .edit-exec-list {
+    display: flex;
+    flex-direction: column;
+    gap: 4px;
+    max-height: 180px;
+    overflow-y: auto;
+  }
+  .edit-exec-option {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    padding: 6px 8px;
+    border-radius: var(--radius-sm);
+    cursor: pointer;
+    font-size: 0.85rem;
+    font-family: var(--font-mono);
+    background: var(--surface);
+    border: 1px solid var(--border);
+    transition: border-color 0.15s, background 0.15s;
+  }
+  .edit-exec-option:hover {
+    border-color: var(--phosphor-dim);
+    background: var(--surface-hover);
+  }
+  .edit-exec-option.selected {
+    border-color: var(--phosphor);
+    background: var(--phosphor-burn);
+  }
+  .edit-exec-option input[type="radio"] {
+    accent-color: var(--phosphor);
+    margin: 0;
+    flex-shrink: 0;
+  }
+  .edit-exec-path {
+    word-break: break-all;
+    color: var(--text);
+  }
+  .edit-exec-option.selected .edit-exec-path {
+    color: var(--phosphor-glow);
+  }
+
   /* ─── Responsive ────────────────────────────────── */
   @media (max-width: 640px) {
     .detail { padding: 16px 0; }

src/main/java/com/dostalgia/Game.java

@@ -23,6 +23,12 @@ public class Game {
 
     private String setupExe;    // relative path to SETUP.EXE (null if none)
 
+    /** Currently selected main executable (relative path inside the bundle, e.g. "FALLOUT.EXE" or "FALLOUT/FALLOUT.EXE"). */
+    private String executable;
+
+    /** All discoverable executables in the bundle (for the UI picker). */
+    private List<String> executables;
+
     /** Platform type: "dos" for pure DOS, "windows" for Windows 3.x/9x+ (requires emulated Windows), null if unknown. */
     private String platform;
 
@@ -85,6 +91,12 @@ public class Game {
     public String getSetupExe() { return setupExe; }
     public void setSetupExe(String setupExe) { this.setupExe = setupExe; }
 
+    public String getExecutable() { return executable; }
+    public void setExecutable(String executable) { this.executable = executable; }
+
+    public List<String> getExecutables() { return executables; }
+    public void setExecutables(List<String> executables) { this.executables = executables; }
+
     /** Returns true if a SETUP.EXE (or variant) was detected in the game archive. */
     public boolean isHasSetup() { return setupExe != null && !setupExe.isBlank(); }
 

src/main/java/com/dostalgia/GameResource.java

@@ -84,7 +84,17 @@ public class GameResource {
             if (updates.containsKey("rating")) game.setRating(asDouble(updates.get("rating")));
             if (updates.containsKey("platform")) game.setPlatform((String) updates.get("platform"));
 
+            // Changing the executable requires patching the .jsdos bundle
+            if (updates.containsKey("executable")) {
+                String newExe = (String) updates.get("executable");
+                if (newExe != null && !newExe.isBlank()) {
+                    svc.setExecutable(id, newExe);
+                }
+                // Reload after bundle patch to get updated metadata
+                game = svc.load(id);
+            } else {
                 svc.save(game);
+            }
             return Response.ok(game).build();
         } catch (NoSuchFileException e) {
             return Response.status(404).entity(Map.of("error", "Game not found")).build();

src/main/java/com/dostalgia/GameService.java

@@ -146,5 +146,134 @@ public class GameService {
         return Files.exists(p);
     }
 
+    /** Patch the .jsdos bundle to use a different main executable. */
+    public void setExecutable(String id, String executable) throws IOException {
+        Game game = load(id);
+        String bundleFile = game.getBundleFile();
+        if (bundleFile == null) {
+            throw new IOException("Game has no bundle file");
+        }
+
+        Path bundlePath = gamesDir.resolve(bundleFile);
+        if (!Files.exists(bundlePath)) {
+            throw new NoSuchFileException("Bundle not found: " + bundleFile);
+        }
+
+        // Build new config entries
+        byte[] newDosboxConf = buildDosboxConfBytes(executable);
+        byte[] newJsdosJson = buildJsdosJsonBytes(executable);
+
+        // Patch the ZIP: read old, write new with modified config entries
+        Path tmpPath = bundlePath.resolveSibling(bundleFile + ".tmp");
+        try (var zis = new java.util.zip.ZipInputStream(Files.newInputStream(bundlePath));
+             var zos = new java.util.zip.ZipOutputStream(Files.newOutputStream(tmpPath))) {
+
+            java.util.zip.ZipEntry entry;
+            while ((entry = zis.getNextEntry()) != null) {
+                String name = entry.getName();
+                if (".jsdos/dosbox.conf".equals(name)) {
+                    zos.putNextEntry(new java.util.zip.ZipEntry(name));
+                    zos.write(newDosboxConf);
+                    zos.closeEntry();
+                } else if (".jsdos/jsdos.json".equals(name)) {
+                    zos.putNextEntry(new java.util.zip.ZipEntry(name));
+                    zos.write(newJsdosJson);
+                    zos.closeEntry();
+                } else {
+                    zos.putNextEntry(new java.util.zip.ZipEntry(name));
+                    zis.transferTo(zos);
+                    zos.closeEntry();
+                }
+                zis.closeEntry();
+            }
+        }
+
+        Files.move(tmpPath, bundlePath, StandardCopyOption.REPLACE_EXISTING);
+
+        // Update metadata
+        game.setExecutable(executable);
+        game.setPlatform(detectPlatformSimple(executable, bundlePath));
+        save(game);
+    }
+
+    /** Build a dosbox.conf for a given executable path. */
+    private byte[] buildDosboxConfBytes(String relExe) {
+        var parts = splitExePath(relExe);
+        String dir = parts[0];
+        String exe = parts[1];
+        StringBuilder sb = new StringBuilder();
+        sb.append("[sdl]\nautolock=true\nusescancodes=true\noutput=surface\n\n");
+        sb.append("[cpu]\ncore=auto\ncycles=auto\n\n");
+        sb.append("[mixer]\nnosound=false\nrate=44100\n\n");
+        sb.append("[sblaster]\nsbtype=sb16\nirq=7\ndma=1\nhdma=5\n\n");
+        sb.append("[dos]\nxms=true\nems=true\numb=true\n\n");
+        sb.append("[autoexec]\n@echo off\nmount c .\nc:\n");
+        if (dir != null) {
+            sb.append("path=c:\\\n");
+            sb.append("cd ").append(dir).append("\n");
+        }
+        sb.append(exe).append("\n");
+        return sb.toString().getBytes(java.nio.charset.StandardCharsets.UTF_8);
+    }
+
+    /** Build jsdos.json for a given executable path. */
+    private byte[] buildJsdosJsonBytes(String relExe) {
+        var parts = splitExePath(relExe);
+        StringBuilder script = new StringBuilder();
+        if (parts[0] != null) {
+            script.append("path=c:\\\n");
+            script.append("cd ").append(parts[0]).append("\n");
+        }
+        script.append(parts[1]);
+        String json = "{"
+            + "\"autoexec\":{"
+            + "\"options\":{\"script\":{\"value\":\"" + escapeJsonValue(script.toString()) + "\"}}"
+            + "},"
+            + "\"output\":{"
+            + "\"options\":{\"autolock\":{\"value\":true}}}"
+            + "}";
+        return json.getBytes(java.nio.charset.StandardCharsets.UTF_8);
+    }
+
+    /** Split "dir/file.exe" into ["dir", "file.exe"]. Returns [null, file] if no dir. */
+    private static String[] splitExePath(String relExe) {
+        int idx = relExe.replace('\\', '/').lastIndexOf('/');
+        if (idx >= 0) {
+            return new String[]{relExe.substring(0, idx), relExe.substring(idx + 1)};
+        }
+        return new String[]{null, relExe};
+    }
+
+    private static String escapeJsonValue(String s) {
+        return s.replace("\\", "\\\\").replace("\"", "\\\"");
+    }
+
+    /** Quick platform detection for a given executable inside a .jsdos bundle. */
+    private String detectPlatformSimple(String relExe, Path bundlePath) throws IOException {
+        // Extract the executable from the ZIP and detect its platform
+        try (var zis = new java.util.zip.ZipInputStream(Files.newInputStream(bundlePath))) {
+            java.util.zip.ZipEntry entry;
+            while ((entry = zis.getNextEntry()) != null) {
+                if (entry.getName().equals(relExe.replace('\\', '/'))) {
+                    byte[] buf = new byte[0x80];
+                    int read = zis.readNBytes(buf, 0, buf.length);
+                    if (read < 2) return null;
+                    if (buf[0] != 0x4D || buf[1] != 0x5A) return null;
+                    if (read < 0x40) return "dos";
+                    // Check for PE/NE at e_lfanew
+                    int peOffset = (buf[0x3C] & 0xFF) | ((buf[0x3D] & 0xFF) << 8)
+                                 | ((buf[0x3E] & 0xFF) << 16) | ((buf[0x3F] & 0xFF) << 24);
+                    if (peOffset < 0 || peOffset + 2 > read) return "dos";
+                    byte sig1 = buf[peOffset], sig2 = buf[peOffset + 1];
+                    if ((sig1 == 0x50 && sig2 == 0x45) || (sig1 == 0x4E && sig2 == 0x45))
+                        return "windows";
+                    return "dos";
+                }
+                zis.closeEntry();
+            }
+        }
+        return null;
+    }
+
     public Path getGamesDir() { return gamesDir; }
 }

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

@@ -120,6 +120,10 @@ public class UploadResource {
             Game game = new Game(gameId, title);
             game.setBundleFile(bundleFile);
             game.setPlatform(platform);
+            // Store the selected executable and the full list for the UI picker
+            String relMain = extractDir.relativize(Path.of(mainExe)).toString().replace('\\', '/');
+            game.setExecutable(relMain);
+            game.setExecutables(findAllExecutables(extractDir));
             if (hasSetupBundle) {
                 game.setSetupExe(extractDir.relativize(Path.of(setupExe)).toString());
             }
@@ -242,6 +246,23 @@ public class UploadResource {
 
     // ─── Executable Detection ────────────────────────────────────
 
+    /** Collect all discoverable executables (relative paths) from the extracted directory. */
+    private List<String> findAllExecutables(Path dir) throws IOException {
+        List<String> result = new ArrayList<>();
+        Files.walkFileTree(dir, new SimpleFileVisitor<>() {
+            @Override
+            public FileVisitResult visitFile(Path f, BasicFileAttributes a) {
+                String name = f.getFileName().toString().toLowerCase();
+                if (name.endsWith(".exe") || name.endsWith(".com") || name.endsWith(".bat")) {
+                    result.add(dir.relativize(f).toString().replace('\\', '/'));
+                }
+                return FileVisitResult.CONTINUE;
+            }
+        });
+        result.sort(String::compareTo);
+        return result;
+    }
+
     private String findMainExe(Path dir) throws IOException {
         record Candidate(int depth, boolean isInstaller, long size, String path, String platform) {}
         List<Candidate> candidates = new ArrayList<>();