fix: allow signal.get() in Binder validators (#23612)

Split the conversion chain into executeConversionChain() (raw, used by
the signal effect for dependency tracking) and doConversion() (always
wrapped in untracked(), used by all other callers). Extract
fireValidationEvents() so the effect can fire events directly. Guard
trackUsageOfInternalValidationSignal() with isActive() to skip work
inside untracked contexts.

Fixes #22123

Author: Artur-

flow-data/src/main/java/com/vaadin/flow/data/binder/Binder.java

@@ -1564,19 +1564,22 @@ protected static Locale findLocale() {
             return locale;
         }
 
+        private void fireValidationEvents(
+                BindingValidationStatus<TARGET> status) {
+            var statusChange = new BinderValidationStatus<>(getBinder(),
+                    Collections.singletonList(status), Collections.emptyList());
+            getBinder().getValidationStatusHandler().statusChange(statusChange);
+            getBinder().signalStatusChangeFromBinding(status);
+            getBinder().fireStatusChangeEvent(status.isError());
+        }
+
         @Override
         public BindingValidationStatus<TARGET> validate(boolean fireEvent) {
             Objects.requireNonNull(binder,
                     "This Binding is no longer attached to a Binder");
             BindingValidationStatus<TARGET> status = doValidation();
             if (fireEvent) {
-                var statusChange = new BinderValidationStatus<>(getBinder(),
-                        Collections.singletonList(status),
-                        Collections.emptyList());
-                getBinder().getValidationStatusHandler()
-                        .statusChange(statusChange);
-                getBinder().signalStatusChangeFromBinding(status);
-                getBinder().fireStatusChangeEvent(status.isError());
+                fireValidationEvents(status);
             }
             return status;
         }
@@ -1615,20 +1618,33 @@ public void unbind() {
         }
 
         /**
-         * Returns the field value run through all converters and validators,
-         * but doesn't pass the {@link BindingValidationStatus} to any status
-         * handler.
+         * Runs the field value through all converters and validators without
+         * wrapping in {@code untracked()}. This allows signal dependency
+         * tracking when called from the reactive effect in
+         * {@link #initInternalSignalEffectForValidators()}.
          *
          * @return the result of the conversion
          */
-        private Result<TARGET> doConversion() {
+        private Result<TARGET> executeConversionChain() {
             return execute(() -> {
                 FIELDVALUE fieldValue = field.getValue();
                 return converterValidatorChain.convertToModel(fieldValue,
                         createValueContext());
             });
         }
 
+        /**
+         * Returns the field value run through all converters and validators,
+         * but doesn't pass the {@link BindingValidationStatus} to any status
+         * handler. Always runs inside {@code untracked()} so that callers
+         * outside a reactive context never trigger signal tracking.
+         *
+         * @return the result of the conversion
+         */
+        private Result<TARGET> doConversion() {
+            return UsageTracker.untracked(this::executeConversionChain);
+        }
+
         private BindingValidationStatus<TARGET> toValidationStatus(
                 Result<TARGET> result) {
             return new BindingValidationStatus<>(result, this);
@@ -1711,11 +1727,12 @@ private void initInternalSignalEffectForValidators() {
             if (signalRegistration == null
                     && getField() instanceof Component component) {
                 signalRegistration = Signal.effect(component, () -> {
-                    if (valueInit) {
-                        // start to track signal usage
-                        doConversion();
-                    } else {
-                        validate();
+                    // Run chain with real tracking to discover signal deps
+                    Result<TARGET> result = executeConversionChain();
+                    if (!valueInit) {
+                        BindingValidationStatus<TARGET> status = toValidationStatus(
+                                result);
+                        fireValidationEvents(status);
                     }
                 });
             }
@@ -1987,6 +2004,9 @@ public TARGET value() {
         }
 
         private void trackUsageOfInternalValidationSignal() {
+            if (!UsageTracker.isActive()) {
+                return;
+            }
             if (internalValidationTriggerSignal == null) {
                 internalValidationTriggerSignal = new ValueSignal<>(false);
             }