Harden diagnostic handling and warning presentation

internal/framework/contracts/correction.go

@@ -126,6 +126,9 @@ func (candidate ModelCandidate) Validate() error {
 }
 
 func ValidateValidationResult(result ValidationResult) error {
+	if err := ValidateProducerDiagnostics(result.Diagnostics); err != nil {
+		return fmt.Errorf("validation diagnostics: %w", err)
+	}
 	if !result.Approved && result.ReasonCode == "" {
 		return errors.New("validation rejection reason code must not be empty")
 	}

internal/framework/contracts/correction_test.go

@@ -75,6 +75,9 @@ func TestCorrectionContractsRejectInvalidContent(t *testing.T) {
 		{"oversized correction guidance", func() error {
 			return ValidateValidationResult(ValidationResult{ReasonCode: "invalid", CorrectionGuidance: tooLongValidationGuidance})
 		}},
+		{"invalid diagnostics", func() error {
+			return ValidateValidationResult(ValidationResult{Approved: true, Diagnostics: []ProducerDiagnostic{{}}})
+		}},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			if err := test.call(); err == nil {

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

internal/framework/contracts/diagnostics_test.go

@@ -146,6 +146,47 @@ func TestCloneDiagnosticCollectionOwnsGroupsAndChunkIndex(t *testing.T) {
 	}
 }
 
+func TestProjectDiagnosticCollectionPartitionsAndChecksTotals(t *testing.T) {
+	warning := validDiagnosticGroup(DiagnosticDispositionWarning, DiagnosticCategoryFallback, "fallback", 2)
+	diagnostic := validDiagnosticGroup(DiagnosticDispositionAdvisory, DiagnosticCategoryDataQuality, "quality", 3)
+	collection := DiagnosticCollection{
+		Groups:                       []DiagnosticGroup{warning, diagnostic},
+		Truncated:                    true,
+		UnrepresentedOccurrenceCount: 4,
+	}
+	projection, err := ProjectDiagnosticCollection(collection)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(projection.Warnings) != 1 || len(projection.Diagnostics) != 1 || projection.WarningOccurrenceCount != 2 || projection.DiagnosticOccurrenceCount != 7 {
+		t.Fatalf("projection = %#v, want partitioned exact totals", projection)
+	}
+	collection.Groups[0].Samples[0].Message = "mutated"
+	if projection.Warnings[0].Samples[0].Message != "message" {
+		t.Fatal("projection retained caller-owned sample storage")
+	}
+
+	overflow := DiagnosticCollection{Groups: []DiagnosticGroup{
+		validDiagnosticGroup(DiagnosticDispositionWarning, DiagnosticCategoryFallback, "first", int(^uint(0)>>1)),
+		validDiagnosticGroup(DiagnosticDispositionWarning, DiagnosticCategoryFallback, "second", 1),
+	}}
+	if _, err := ProjectDiagnosticCollection(overflow); err == nil {
+		t.Fatal("ProjectDiagnosticCollection() overflow error = nil")
+	}
+}
+
+func validDiagnosticGroup(disposition DiagnosticDisposition, category DiagnosticCategory, reason string, occurrences int) DiagnosticGroup {
+	return DiagnosticGroup{
+		Disposition:        disposition,
+		Category:           category,
+		ReasonCode:         reason,
+		Origin:             DiagnosticOrigin{Stage: DiagnosticOriginStageNormalize, StepID: "step", LaneID: "lane", ModuleKey: "module"},
+		OccurrenceCount:    occurrences,
+		Samples:            []DiagnosticSample{{Scope: "scope", Message: "message"}},
+		OmittedSampleCount: occurrences - 1,
+	}
+}
+
 func validProducerDiagnostic() ProducerDiagnostic {
 	return ProducerDiagnostic{
 		Disposition:     DiagnosticDispositionWarning,