Harden diagnostic handling and warning presentation

internal/framework/contracts/diagnostics.go

@@ -102,6 +102,16 @@ type DiagnosticCollection struct {
 	UnrepresentedOccurrenceCount int               `json:"unrepresented_occurrence_count"`
 }
 
+// DiagnosticProjection is the validated warning/non-warning view used by
+// durable and presentation boundaries. Occurrence totals are checked before
+// they leave the framework contract.
+type DiagnosticProjection struct {
+	Warnings                  []DiagnosticGroup
+	Diagnostics               []DiagnosticGroup
+	WarningOccurrenceCount    int
+	DiagnosticOccurrenceCount int
+}
+
 // Validate checks a producer-local diagnostic against the public safety and
 // classification contract.
 func (diagnostic ProducerDiagnostic) Validate() error {
@@ -192,6 +202,41 @@ func (collection DiagnosticCollection) Validate() error {
 	return nil
 }
 
+// ProjectDiagnosticCollection validates, partitions, and totals one finalized
+// collection. Unrepresented occurrences belong to the non-warning projection.
+func ProjectDiagnosticCollection(collection DiagnosticCollection) (DiagnosticProjection, error) {
+	if err := collection.Validate(); err != nil {
+		return DiagnosticProjection{}, err
+	}
+	projection := DiagnosticProjection{
+		Warnings:    make([]DiagnosticGroup, 0),
+		Diagnostics: make([]DiagnosticGroup, 0),
+	}
+	for _, group := range collection.Groups {
+		if group.Disposition == DiagnosticDispositionWarning {
+			count, err := addDiagnosticOccurrences(projection.WarningOccurrenceCount, group.OccurrenceCount)
+			if err != nil {
+				return DiagnosticProjection{}, fmt.Errorf("warning occurrences: %w", err)
+			}
+			projection.WarningOccurrenceCount = count
+			projection.Warnings = append(projection.Warnings, cloneDiagnosticGroup(group))
+			continue
+		}
+		count, err := addDiagnosticOccurrences(projection.DiagnosticOccurrenceCount, group.OccurrenceCount)
+		if err != nil {
+			return DiagnosticProjection{}, fmt.Errorf("diagnostic occurrences: %w", err)
+		}
+		projection.DiagnosticOccurrenceCount = count
+		projection.Diagnostics = append(projection.Diagnostics, cloneDiagnosticGroup(group))
+	}
+	count, err := addDiagnosticOccurrences(projection.DiagnosticOccurrenceCount, collection.UnrepresentedOccurrenceCount)
+	if err != nil {
+		return DiagnosticProjection{}, fmt.Errorf("diagnostic occurrences: %w", err)
+	}
+	projection.DiagnosticOccurrenceCount = count
+	return projection, nil
+}
+
 // CloneProducerDiagnostics returns independent diagnostic slice ownership.
 func CloneProducerDiagnostics(diagnostics []ProducerDiagnostic) []ProducerDiagnostic {
 	if len(diagnostics) == 0 {
@@ -305,6 +350,13 @@ func cloneDiagnosticGroup(group DiagnosticGroup) DiagnosticGroup {
 	return group
 }
 
+func addDiagnosticOccurrences(current, incoming int) (int, error) {
+	if incoming > int(^uint(0)>>1)-current {
+		return 0, errors.New("occurrence count overflow")
+	}
+	return current + incoming, nil
+}
+
 func cloneDiagnosticSamples(samples []DiagnosticSample) []DiagnosticSample {
 	if len(samples) == 0 {
 		return nil