Add platform auto-detection and UI flagging for Windows games

- Game.java: add 'platform' field ('dos'/'windows') + 'isPlayable' helper
- UploadResource.java: detect EXE type by reading PE/NE header during upload
- GameResource.java: allow PATCH to update platform
- GameCard.svelte: show 🪟 Win badge for Windows games (blue style)
- GameDetail.svelte: show platform badge, disable Play for Windows with
  'Unplayable' button; add platform dropdown to edit form
- Play.svelte: show blocking overlay for Windows games with 'Try anyway'
  option for users who want to attempt it

frontend/src/lib/GameCard.svelte

@@ -29,7 +29,13 @@
     {/if}
   </div>
   {#if game.ready}
-    <div class="badge">Ready</div>
+    <div class="badge" class:badge-windows={game.platform === 'windows'}>
+      {#if game.platform === 'windows'}
+        🪟 Win
+      {:else}
+        Ready
+      {/if}
+    </div>
   {/if}
 </button>
 
@@ -111,4 +117,8 @@
     font-weight: 600;
     letter-spacing: 0.05em;
   }
+  .badge-windows {
+    background: #1a3a5c;
+    color: #6ab0ff;
+  }
 </style>

frontend/src/pages/GameDetail.svelte

@@ -16,6 +16,7 @@
   let editDeveloper = $state("");
   let editPublisher = $state("");
   let editDescription = $state("");
+  let editPlatform = $state("");
 
   // IGDB scrape state
   let scraping = $state(false);
@@ -63,6 +64,7 @@
     editDeveloper = game.developer || "";
     editPublisher = game.publisher || "";
     editDescription = game.description || "";
+    editPlatform = game.platform || "";
     editing = true;
   }
 
@@ -76,6 +78,7 @@
         developer: editDeveloper || undefined,
         publisher: editPublisher || undefined,
         description: editDescription || undefined,
+        platform: editPlatform || undefined,
       });
       editing = false;
     } catch (e) {
@@ -193,6 +196,13 @@
             <input type="text" bind:value={editPublisher} placeholder="Publisher" style="flex:1" />
           </div>
           <textarea bind:value={editDescription} placeholder="Description" rows="4"></textarea>
+          <div class="edit-row">
+            <select bind:value={editPlatform} style="flex:1">
+              <option value="">Auto (unknown)</option>
+              <option value="dos">DOS</option>
+              <option value="windows">Windows</option>
+            </select>
+          </div>
           <div class="edit-actions">
             <button class="btn btn-primary" onclick={saveEdit} disabled={saving}>
               {saving ? "Saving..." : "Save"}
@@ -201,13 +211,26 @@
           </div>
         {:else}
           <h1>{game.title}</h1>
+          {#if game.platform}
+            <div class="platform-badge" class:platform-win={game.platform === 'windows'}>
+              {#if game.platform === 'windows'}
+                🪟 Requires Windows 3.1 — may not work in browser
+              {:else}
+                💾 DOS
+              {/if}
+            </div>
+          {/if}
           {#if game.description}
             <p class="description">{game.description}</p>
           {/if}
 
           <div class="actions">
-            {#if game.ready}
+            {#if game.ready && (game.platform !== 'windows')}
               <button class="btn btn-primary" onclick={handlePlay}>▶ Play</button>
+            {:else if game.ready && game.platform === 'windows'}
+              <button class="btn btn-primary btn-disabled" disabled title="Windows games need Windows 3.1 emulation (not yet supported)">
+                ▶ Unplayable
+              </button>
             {/if}
             {#if game.has_setup}
               <button class="btn btn-setup" onclick={handleSetup}>🛠 Setup</button>
@@ -347,6 +370,20 @@
   .cover-img { width: 100%; border-radius: var(--radius); }
   .cover-placeholder { aspect-ratio: 3/4; background: var(--surface); display: flex; align-items: center; justify-content: center; font-size: 4rem; border-radius: var(--radius); }
   .info-section h1 { color: var(--phosphor); font-family: var(--font-mono); margin-bottom: 8px; word-break: break-word; }
+  .platform-badge {
+    display: inline-block;
+    font-size: 0.8rem;
+    padding: 3px 10px;
+    border-radius: 10px;
+    font-weight: 600;
+    margin-bottom: 8px;
+    background: var(--phosphor-dark);
+    color: var(--phosphor);
+  }
+  .platform-badge.platform-win {
+    background: #1a3a5c;
+    color: #6ab0ff;
+  }
   .meta { display: flex; gap: 8px; margin-bottom: 8px; }
   .meta-item { background: var(--surface-hover); color: var(--phosphor-dim); padding: 4px 12px; border-radius: 12px; font-size: 0.85rem; }
   .dev { color: var(--text-dim); margin-bottom: 16px; }

frontend/src/pages/Play.svelte

@@ -12,6 +12,7 @@
   let error = $state("");
   let booting = $state(false);
   let running = $state(false);
+  let unsupported = $state(false);
   let started = false;
 
   let dosContainer;
@@ -23,6 +24,10 @@
     isSetup = window.location.hash.includes("setup=1");
     try {
       game = await getGame(id);
+      // Windows games can't run in pure DOSBox — flag it
+      if (game.platform === 'windows') {
+        unsupported = true;
+      }
     } catch (e) {
       error = "Game not found";
     }
@@ -76,6 +81,11 @@
     window.location.reload();
   }
 
+  function handleTryAnyway() {
+    unsupported = false;
+    startEmulator();
+  }
+
   function goBack() {
     push(`/game/${id}`);
   }
@@ -84,7 +94,7 @@
 
   // Auto-start when both game data and the container exist
   $effect(() => {
-    if (game?.ready && dosContainer && !started) {
+    if (game?.ready && dosContainer && !started && !unsupported) {
       startEmulator();
     }
   });
@@ -121,6 +131,19 @@
     <div class="error-box">{error}</div>
   {/if}
 
+  <!-- Unsupported platform warning -->
+  {#if unsupported}
+    <div class="overlay">
+      <div class="overlay-icon">🪟</div>
+      <h2>Windows game</h2>
+      <p><strong>{game.title}</strong> is a Windows application and won't run in the browser DOS emulator without Windows 3.1 installed.</p>
+      <div class="unsupported-actions">
+        <button class="btn btn-secondary" onclick={goBack}>← Back</button>
+        <button class="btn" onclick={handleTryAnyway}>Try anyway</button>
+      </div>
+    </div>
+  {/if}
+
   <!-- Loading / booting overlay (covers the canvas while loading) -->
   {#if !running}
     <div class="overlay">
@@ -256,4 +279,9 @@
     border-radius: var(--radius);
     z-index: 10;
   }
+  .unsupported-actions {
+    display: flex;
+    gap: 12px;
+    margin-top: 20px;
+  }
 </style>

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

@@ -23,6 +23,9 @@ public class Game {
 
     private String setupExe;    // relative path to SETUP.EXE (null if none)
 
+    /** Platform type: "dos" for pure DOS, "windows" for Windows 3.x/9x+ (requires emulated Windows), null if unknown. */
+    private String platform;
+
     private Integer igdbId;
     private String igdbCoverId;
 
@@ -85,6 +88,14 @@ public class Game {
     /** Returns true if a SETUP.EXE (or variant) was detected in the game archive. */
     public boolean isHasSetup() { return setupExe != null && !setupExe.isBlank(); }
 
+    public String getPlatform() { return platform; }
+    public void setPlatform(String platform) { this.platform = platform; }
+
+    /** Returns true if the game is a pure DOS executable that can run natively in DOSBox. */
+    public boolean isPlayable() {
+        return ready && (platform == null || "dos".equals(platform));
+    }
+
     public Integer getIgdbId() { return igdbId; }
     public void setIgdbId(Integer igdbId) { this.igdbId = igdbId; }
 

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

@@ -82,6 +82,7 @@ public class GameResource {
             if (updates.containsKey("publisher")) game.setPublisher((String) updates.get("publisher"));
             if (updates.containsKey("description")) game.setDescription((String) updates.get("description"));
             if (updates.containsKey("rating")) game.setRating(asDouble(updates.get("rating")));
+            if (updates.containsKey("platform")) game.setPlatform((String) updates.get("platform"));
 
             svc.save(game);
             return Response.ok(game).build();

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

@@ -91,9 +91,13 @@ public class UploadResource {
                 createBundle(extractDir, setupExe, setupBundlePath);
             }
 
+            // Detect platform (DOS vs Windows) by reading the main EXE header
+            String platform = detectPlatform(Path.of(mainExe));
+
             // Save metadata
             Game game = new Game(gameId, title);
             game.setBundleFile(bundleFile);
+            game.setPlatform(platform);
             game.setSetupExe(setupExe != null ? extractDir.relativize(Path.of(setupExe)).toString() : null);
             game.setReady(true);
             svc.save(game);
@@ -382,6 +386,64 @@ public class UploadResource {
         return s.replace("\\", "\\\\").replace("\"", "\\\"");
     }
 
+    /**
+     * Detect whether an executable targets DOS or Windows by reading its PE/NE header.
+     * <ul>
+     *   <li>Pure MZ (no NE/PE/LE) → "dos"</li>
+     *   <li>NE (Windows 3.x), PE (Win32), LE (VxD) → "windows"</li>
+     *   <li>Cannot read → null</li>
+     * </ul>
+     */
+    static String detectPlatform(Path exePath) {
+        String name = exePath.getFileName().toString().toLowerCase();
+        // .com and .bat files are always DOS
+        if (name.endsWith(".com") || name.endsWith(".bat")) return "dos";
+
+        try (var fis = Files.newInputStream(exePath)) {
+            byte[] buf = new byte[0x80];
+            int read = fis.readNBytes(buf, 0, buf.length);
+            if (read < 2) return null;
+
+            // Must start with MZ
+            if (buf[0] != 0x4D || buf[1] != 0x5A) return null;
+
+            // Read e_lfanew at offset 0x3C
+            if (read < 0x40) return "dos"; // too short for PE/NE, assume DOS
+            int peOffset = (buf[0x3C] & 0xFF)
+                         | ((buf[0x3D] & 0xFF) << 8)
+                         | ((buf[0x3E] & 0xFF) << 16)
+                         | ((buf[0x3F] & 0xFF) << 24);
+
+            // If signature is beyond our buffer, read it
+            byte sig1, sig2;
+            if (peOffset + 2 <= read) {
+                sig1 = buf[peOffset];
+                sig2 = buf[peOffset + 1];
+            } else {
+                try (var fis2 = Files.newInputStream(exePath)) {
+                    fis2.skip(peOffset);
+                    sig1 = (byte) fis2.read();
+                    sig2 = (byte) fis2.read();
+                }
+            }
+
+            // PE  = Portable Executable (Win32)
+            // NE  = New Executable (Windows 3.x)
+            // LE  = Linear Executable (VxD, OS/2)
+            // LX  = Extended Linear Executable (OS/2 2.x)
+            if ((sig1 == 0x50 && sig2 == 0x45)   // PE
+             || (sig1 == 0x4E && sig2 == 0x45)   // NE
+             || (sig1 == 0x4C && sig2 == 0x45)   // LE
+             || (sig1 == 0x4C && sig2 == 0x58))  // LX
+                return "windows";
+
+            return "dos"; // Plain MZ without known Windows signature
+        } catch (IOException e) {
+            LOG.warning("Could not read EXE header for " + exePath + ": " + e.getMessage());
+            return null;
+        }
+    }
+
     // ─── File Utilities ──────────────────────────────────────────
 
     private void deleteDir(Path dir) throws IOException {