feat: add Sierra game bundle patcher and API endpoint

Handles common Sierra game file layout issues:
- RESOURCE.CFG with directory paths pointing to \KQ6CD when
  resources are actually at the bundle root (fixes paths to '.')
- INTERP.ERR/INTERP.ERRC files buried in subdirectories instead
  of at root (copies them up so SIERRA.EXE can find them)

POST /api/games/{id}/patch-sierra triggers the fix on an existing
game bundle.

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

@@ -131,6 +131,23 @@ public class GameResource {
         }
     }
 
+    /**
+     * Patch a Sierra game bundle to fix common file layout issues
+     * (INTERP.ERR paths, RESOURCE.CFG directories).
+     */
+    @POST
+    @Path("/{id}/patch-sierra")
+    public Response patchSierra(@PathParam("id") String id) {
+        try {
+            var patched = svc.patchSierraGame(id);
+            return Response.ok(Map.of("patched", patched)).build();
+        } catch (NoSuchFileException e) {
+            return Response.status(404).entity(Map.of("error", "Game not found")).build();
+        } catch (Exception e) {
+            return Response.serverError().entity(Map.of("error", e.getMessage())).build();
+        }
+    }
+
     @GET
     @Path("/{id}/download")
     @Produces("application/zip")

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

@@ -322,5 +322,154 @@ public class GameService {
         }
     }
 
+    /**
+     * Patch a .jsdos bundle for Sierra games that have file layout issues:
+     * - INTERP.ERR(C) in a subdirectory instead of root (causes "Can't find" errors)
+     * - RESOURCE.CFG directory paths pointing to wrong locations
+     * Returns the list of files that were modified.
+     */
+    public List<String> patchSierraGame(String id) throws IOException {
+        Game game = load(id);
+        Path bundlePath = gamesDir.resolve(game.getBundleFile());
+        if (!Files.exists(bundlePath)) {
+            throw new NoSuchFileException("Bundle not found: " + game.getBundleFile());
+        }
+
+        Path tmpPath = bundlePath.resolveSibling(bundlePath.getFileName() + ".patchtmp");
+        List<String> patched = new ArrayList<>();
+
+        try (var zis = new java.util.zip.ZipInputStream(Files.newInputStream(bundlePath));
+             var zos = new java.util.zip.ZipOutputStream(Files.newOutputStream(tmpPath))) {
+
+            // First pass: read all entries to find INTERP files in subdirs
+            // We can't buffer the whole zip, so we do the copy in one pass
+            // and apply known fixes on the fly.
+
+            // Read the RESOURCE.CFG for Sierra directory detection
+            // We do this by pre-scanning the zip (streaming approach)
+
+            java.util.zip.ZipEntry entry;
+            while ((entry = zis.getNextEntry()) != null) {
+                String name = entry.getName();
+                zos.putNextEntry(new java.util.zip.ZipEntry(name));
+
+                if (name.equals("RESOURCE.CFG")) {
+                    // Read, patch, write
+                    byte[] content = zis.readAllBytes();
+                    String text = new String(content, java.nio.charset.StandardCharsets.ISO_8859_1);
+                    String original = text;
+
+                    // Fix directory paths pointing to a subdir when resources are at root
+                    text = text.replaceAll("(?m)^directory\\s*=\\\\?.+", "directory = .");
+                    text = text.replaceAll("(?m)^audio\\s*=\\s*[A-Za-z]:\\\\?.+", "audio = .");
+                    text = text.replaceAll("(?m)^sync\\s*=\\s*[A-Za-z]:\\\\?.+", "sync = .");
+                    text = text.replaceAll("(?m)^movieDir\\s*=\\s*[A-Za-z]:\\\\?.+", "movieDir = .\\\\SEQ");
+                    text = text.replaceAll("(?m)^patchDir\\s*=\\s*[A-Za-z]:\\\\?.+", "patchDir = .");
+
+                    if (!text.equals(original)) {
+                        patched.add("RESOURCE.CFG (fixed paths)");
+                        zos.write(text.getBytes(java.nio.charset.StandardCharsets.ISO_8859_1));
+                    } else {
+                        zos.write(content);
+                    }
+                } else {
+                    // For all other files, check if we need to add INTERP.ERR(C) copies
+                    zis.transferTo(zos);
+                }
+                zos.closeEntry();
+                zis.closeEntry();
+            }
+
+            // Second pass: scan for INTERP files in subdirectories
+            // We need to re-read the zip for this. Use a clean approach.
+        }
+
+        // If RESOURCE.CFG was not patched, check for INTERP.ERR and add it
+        boolean needsInterpFix = false;
+        String interpSource = null;
+
+        // Re-scan the original bundle for INTERP files in subdirs
+        try (var zis = new java.util.zip.ZipInputStream(Files.newInputStream(bundlePath))) {
+            java.util.zip.ZipEntry entry;
+            while ((entry = zis.getNextEntry()) != null) {
+                String name = entry.getName();
+                if (!name.startsWith(".jsdos/") && name.contains("/") &&
+                    (name.endsWith("/INTERP.ERR") || name.endsWith("/INTERP.ERRC"))) {
+                    // Found an INTERP file in a subdirectory
+                    String rootName = name.substring(name.lastIndexOf('/') + 1);
+                    interpSource = name;
+                    break;
+                }
+                zis.closeEntry();
+            }
+        }
+
+        if (interpSource != null) {
+            // Check if INTERP file already exists at root in the patched bundle
+            boolean hasRootInterp = false;
+            try (var zis = new java.util.zip.ZipInputStream(Files.newInputStream(tmpPath))) {
+                java.util.zip.ZipEntry entry;
+                while ((entry = zis.getNextEntry()) != null) {
+                    String name = entry.getName();
+                    if (name.equals("INTERP.ERR") || name.equals("INTERP.ERRC")) {
+                        hasRootInterp = true;
+                        break;
+                    }
+                    zis.closeEntry();
+                }
+            }
+
+            if (!hasRootInterp) {
+                // Read the INTERP file from original bundle and append it
+                byte[] interpData = null;
+                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(interpSource)) {
+                            interpData = zis.readAllBytes();
+                            break;
+                        }
+                        zis.closeEntry();
+                    }
+                }
+
+                if (interpData != null) {
+                    // Append to the patched bundle
+                    String rootName = interpSource.substring(interpSource.lastIndexOf('/') + 1);
+                    try (var zis2 = new java.util.zip.ZipInputStream(Files.newInputStream(tmpPath));
+                         var tmp2 = new java.util.zip.ZipOutputStream(Files.newOutputStream(
+                             tmpPath.resolveSibling(bundlePath.getFileName() + ".patchtmp2")))) {
+                        java.util.zip.ZipEntry e;
+                        while ((e = zis2.getNextEntry()) != null) {
+                            tmp2.putNextEntry(new java.util.zip.ZipEntry(e.getName()));
+                            zis2.transferTo(tmp2);
+                            tmp2.closeEntry();
+                            zis2.closeEntry();
+                        }
+                        // Add INTERP file at root
+                        tmp2.putNextEntry(new java.util.zip.ZipEntry(rootName));
+                        tmp2.write(interpData);
+                        tmp2.closeEntry();
+                        zis2.close();
+                        tmp2.close();
+                    }
+                    Files.delete(tmpPath);
+                    Path tmp2 = tmpPath.resolveSibling(bundlePath.getFileName() + ".patchtmp2");
+                    Files.move(tmp2, tmpPath);
+                    patched.add(rootName + " (copied from " + interpSource + ")");
+                }
+            }
+        }
+
+        // If nothing was patched, clean up and return empty
+        if (patched.isEmpty()) {
+            Files.deleteIfExists(tmpPath);
+            return patched;
+        }
+
+        Files.move(tmpPath, bundlePath, StandardCopyOption.REPLACE_EXISTING);
+        return patched;
+    }
+
     public Path getGamesDir() { return gamesDir; }
 }