feat(storage): add ArtifactCoordinates value type

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

@@ -0,0 +1,27 @@
+package com.cameleer.server.core.storage;
+
+import java.util.UUID;
+
+/**
+ * Opaque coordinate that addresses one stored JAR. Designed so a future
+ * OCI-backed store can reuse the same coordinate without schema changes —
+ * see issue (Zot follow-up).
+ */
+public record ArtifactCoordinates(String tenantId, UUID appId, int version) {
+    public ArtifactCoordinates {
+        if (tenantId == null) throw new IllegalArgumentException("tenantId must not be null");
+        if (appId == null) throw new IllegalArgumentException("appId must not be null");
+        if (version <= 0) throw new IllegalArgumentException("version must be > 0, got " + version);
+    }
+
+    /** Path-fragment used by FilesystemArtifactStore. Mirrors today's layout. */
+    public String filesystemKey() {
+        return appId + "/v" + version + "/app.jar";
+    }
+
+    /** OCI reference used by a future registry-backed store. Stable so coordinates
+     * survive a backend swap. */
+    public String ociRef() {
+        return tenantId + "/" + appId + ":v" + version;
+    }
+}

cameleer-server-core/src/test/java/com/cameleer/server/core/storage/ArtifactCoordinatesTest.java

@@ -0,0 +1,33 @@
+package com.cameleer.server.core.storage;
+
+import org.junit.jupiter.api.Test;
+import java.util.UUID;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class ArtifactCoordinatesTest {
+    @Test
+    void rejectsNullsAndNonPositiveVersion() {
+        UUID appId = UUID.randomUUID();
+        assertThatThrownBy(() -> new ArtifactCoordinates(null, appId, 1))
+                .isInstanceOf(IllegalArgumentException.class);
+        assertThatThrownBy(() -> new ArtifactCoordinates("default", null, 1))
+                .isInstanceOf(IllegalArgumentException.class);
+        assertThatThrownBy(() -> new ArtifactCoordinates("default", appId, 0))
+                .isInstanceOf(IllegalArgumentException.class);
+    }
+
+    @Test
+    void filesystemKeyMatchesLegacyLayout() {
+        UUID appId = UUID.fromString("11111111-1111-1111-1111-111111111111");
+        ArtifactCoordinates c = new ArtifactCoordinates("default", appId, 7);
+        assertThat(c.filesystemKey()).isEqualTo("11111111-1111-1111-1111-111111111111/v7/app.jar");
+    }
+
+    @Test
+    void ociRefIsDeterministic() {
+        UUID appId = UUID.fromString("11111111-1111-1111-1111-111111111111");
+        ArtifactCoordinates c = new ArtifactCoordinates("acme", appId, 7);
+        assertThat(c.ociRef()).isEqualTo("acme/11111111-1111-1111-1111-111111111111:v7");
+    }
+}