fix: resolve 8 SonarQube reliability bugs

- ElkDiagramRenderer: guard against null containingNode before getElkRoot()
- OpenSearchAdminController: return 503/502 instead of 200 on errors
- DatabaseAdminController: return 503 instead of 200 on connection failure
- SpaForwardController: replace unbound {path} variables with /** wildcards
- WriteBuffer: check offer() return value and log on unexpected rejection
- ApiExceptionHandler: extract getReason() to local var for null safety
- Admin UI pages: handle isError state for disconnected service display

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cameleer3-server-app/src/main/java/com/cameleer3/server/app/controller/ApiExceptionHandler.java

@@ -14,7 +14,8 @@ public class ApiExceptionHandler {
 
     @ExceptionHandler(ResponseStatusException.class)
     public ResponseEntity<ErrorResponse> handleResponseStatus(ResponseStatusException ex) {
+        String reason = ex.getReason();
         return ResponseEntity.status(ex.getStatusCode())
-                .body(new ErrorResponse(ex.getReason() != null ? ex.getReason() : "Unknown error"));
+                .body(new ErrorResponse(reason != null ? reason : "Unknown error"));
     }
 }

cameleer3-server-app/src/main/java/com/cameleer3/server/app/controller/DatabaseAdminController.java

@@ -59,7 +59,8 @@ public class DatabaseAdminController {
             String host = extractHost(dataSource);
             return ResponseEntity.ok(new DatabaseStatusResponse(true, version, host, schema, timescaleDb));
         } catch (Exception e) {
-            return ResponseEntity.ok(new DatabaseStatusResponse(false, null, null, null, false));
+            return ResponseEntity.status(HttpStatus.SERVICE_UNAVAILABLE)
+                    .body(new DatabaseStatusResponse(false, null, null, null, false));
         }
     }
 

cameleer3-server-app/src/main/java/com/cameleer3/server/app/controller/OpenSearchAdminController.java

@@ -80,7 +80,8 @@ public class OpenSearchAdminController {
                     health.numberOfNodes(),
                     opensearchUrl));
         } catch (Exception e) {
-            return ResponseEntity.ok(new OpenSearchStatusResponse(
+            return ResponseEntity.status(HttpStatus.SERVICE_UNAVAILABLE)
+                    .body(new OpenSearchStatusResponse(
                     false, "UNREACHABLE", null, 0, opensearchUrl));
         }
     }
@@ -149,7 +150,8 @@ public class OpenSearchAdminController {
                     pageItems, totalIndices, totalDocs,
                     humanSize(totalBytes), page, size, totalPages));
         } catch (Exception e) {
-            return ResponseEntity.ok(new IndicesPageResponse(
+            return ResponseEntity.status(HttpStatus.BAD_GATEWAY)
+                    .body(new IndicesPageResponse(
                     List.of(), 0, 0, "0 B", page, size, 0));
         }
     }
@@ -234,7 +236,8 @@ public class OpenSearchAdminController {
                     searchLatency, indexingLatency,
                     heapUsed, heapMax));
         } catch (Exception e) {
-            return ResponseEntity.ok(new PerformanceResponse(0, 0, 0, 0, 0, 0));
+            return ResponseEntity.status(HttpStatus.BAD_GATEWAY)
+                    .body(new PerformanceResponse(0, 0, 0, 0, 0, 0));
         }
     }
 

cameleer3-server-app/src/main/java/com/cameleer3/server/app/diagram/ElkDiagramRenderer.java

@@ -415,12 +415,13 @@ public class ElkDiagramRenderer implements DiagramRenderer {
         for (ElkEdge elkEdge : allEdges) {
             String sourceId = elkEdge.getSources().isEmpty() ? "" : elkEdge.getSources().get(0).getIdentifier();
             String targetId = elkEdge.getTargets().isEmpty() ? "" : elkEdge.getTargets().get(0).getIdentifier();
-            ElkNode edgeRoot = getElkRoot(elkEdge.getContainingNode());
+            ElkNode containingNode = elkEdge.getContainingNode();
+            ElkNode edgeRoot = containingNode != null ? getElkRoot(containingNode) : null;
 
             List<double[]> points = new ArrayList<>();
             for (ElkEdgeSection section : elkEdge.getSections()) {
-                double cx = getAbsoluteX(elkEdge.getContainingNode(), edgeRoot);
-                double cy = getAbsoluteY(elkEdge.getContainingNode(), edgeRoot);
+                double cx = containingNode != null ? getAbsoluteX(containingNode, edgeRoot) : 0;
+                double cy = containingNode != null ? getAbsoluteY(containingNode, edgeRoot) : 0;
                 points.add(new double[]{section.getStartX() + cx, section.getStartY() + cy});
                 for (ElkBendPoint bp : section.getBendPoints()) {
                     points.add(new double[]{bp.getX() + cx, bp.getY() + cy});

cameleer3-server-app/src/main/java/com/cameleer3/server/app/web/SpaForwardController.java

@@ -16,9 +16,9 @@ public class SpaForwardController {
     @GetMapping(value = {
             "/login",
             "/executions",
-            "/executions/{path:[^\\.]*}",
+            "/executions/**",
             "/oidc/callback",
-            "/admin/{path:[^\\.]*}"
+            "/admin/**"
     })
     public String forward() {
         return "forward:/index.html";