Make chunk validation a framework contract

internal/framework/pipeline/runner.go

@@ -91,6 +91,7 @@ func (r *Runner) Run(ctx context.Context, input RunInput) (RunOutput, error) {
 	}
 	chunkResult, err := chunker.Chunk(ctx, contracts.ChunkRequest{
 		Source:     doc,
+		LLMClient:  input.LLMClient,
 		LLMProfile: input.Pipeline.Chunk.LLMProfile,
 		Options:    cloneOptions(input.Pipeline.Chunk.Options),
 		Metadata:   input.Metadata,
@@ -102,6 +103,9 @@ func (r *Runner) Run(ctx context.Context, input RunInput) (RunOutput, error) {
 	if len(chunkResult.Chunks) == 0 {
 		return failOutput(output), fmt.Errorf("chunker %q returned no chunks", chunker.Key())
 	}
+	if err := validateChunkResult(doc, chunkResult.Chunks); err != nil {
+		return failOutput(output), fmt.Errorf("validate chunks from chunker %q: %w", chunker.Key(), err)
+	}
 
 	nextCandidateIndex := 0
 	for _, lane := range input.Pipeline.ArtifactLanes {