Add source highlighting and revision-checked diagnostic fixes in both hosts

designer-core/src/main/java/de/neitzel/fxdesigner/host/HostServices.java

@@ -91,13 +91,46 @@ public record HostServices(
     ERROR
   }
 
+  /** Half-open UTF-16 range in the authoritative source. */
+  public record SourceRange(int start, int end) {
+    public SourceRange {
+      if (start < 0 || end < start) throw new IllegalArgumentException("Invalid diagnostic range");
+    }
+  }
+
+  public record QuickFix(
+      String label, List<de.neitzel.fxdesigner.contracts.EditBatch.Replacement> edits) {
+    public QuickFix {
+      if (label == null || label.isBlank()) throw new IllegalArgumentException("Missing fix label");
+      edits = List.copyOf(edits);
+      if (edits.isEmpty()) throw new IllegalArgumentException("Empty fix");
+    }
+
+    @Override
+    public String toString() {
+      return label;
+    }
+  }
+
   public record Diagnostic(
-      String operation, Severity severity, String message, Optional<Location> location) {
+      String operation,
+      Severity severity,
+      String message,
+      Optional<Location> location,
+      Optional<SourceRange> range,
+      List<QuickFix> fixes) {
+    public Diagnostic(
+        String operation, Severity severity, String message, Optional<Location> location) {
+      this(operation, severity, message, location, Optional.empty(), List.of());
+    }
+
     public Diagnostic {
       Objects.requireNonNull(operation);
       Objects.requireNonNull(severity);
       Objects.requireNonNull(message);
       Objects.requireNonNull(location);
+      Objects.requireNonNull(range);
+      fixes = List.copyOf(fixes);
     }
   }
 
@@ -111,6 +144,16 @@ public record HostServices(
         String context,
         List<Diagnostic> diagnostics) {}
 
+    /** Fix execution stays with the shared editor's revision-checked host transaction. */
+    default void replace(
+        String owner,
+        de.neitzel.fxdesigner.contracts.DocumentSnapshot source,
+        String context,
+        List<Diagnostic> diagnostics,
+        Consumer<QuickFix> apply) {
+      replace(owner, source, context, diagnostics);
+    }
+
     /** Withdraw this editor's diagnostics without removing another editor's results. */
     default void clear(String owner) {}
   }