refactor(web): authoritative Content-Length, typed Optional<AppVersion> in controller

cameleer-server-core/src/main/java/com/cameleer/server/core/runtime/AppService.java

@@ -13,6 +13,7 @@ import java.security.MessageDigest;
 import java.util.HexFormat;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.UUID;
 import java.util.regex.Pattern;
 
@@ -57,6 +58,13 @@ public class AppService {
                 .orElseThrow(() -> new IllegalArgumentException("AppVersion not found: " + versionId));
     }
 
+    /** Typed Optional accessor for callers that distinguish missing-rows from
+     * other failures without relying on the message-based exception convention
+     * of {@link #getVersion(UUID)}. */
+    public Optional<AppVersion> findVersion(UUID versionId) {
+        return versionRepo.findById(versionId);
+    }
+
     /** Coordinate corresponding to an AppVersion. Used by callers that need to
      *  pass the artifact identity to {@link ArtifactStore} (download, delete, exists). */
     public ArtifactCoordinates coordinatesFor(AppVersion version) {

cameleer-server-core/src/main/java/com/cameleer/server/core/storage/ArtifactStore.java

@@ -22,6 +22,11 @@ public interface ArtifactStore {
     /** Open the artifact for reading. Caller closes. */
     InputStream get(ArtifactCoordinates coords) throws IOException;
 
+    /** Size of the stored artifact in bytes. Authoritative — read from the backend
+     * at serve time so a stale {@code AppVersion.jarSizeBytes} cannot silently
+     * truncate downloads. */
+    long size(ArtifactCoordinates coords) throws IOException;
+
     /** True if an artifact is currently stored under {@code coords}. */
     boolean exists(ArtifactCoordinates coords);