Make validation cancellation authoritative

internal/validate/validator.go

@@ -7,11 +7,16 @@ import (
 )
 
 // Validator validates the generated artifact based on the output contract.
+// Validation checks ctx around Promptkit-controlled work and synchronous
+// dependency calls. A dependency call already in progress cannot be preempted;
+// after it returns, cancellation takes precedence over its result.
 type Validator interface {
 	Validate(ctx context.Context, artifact *domain.Artifact, contract domain.OutputContract) (domain.ValidationResult, error)
 }
 
 // PreparedValidation validates artifacts against one frozen output contract.
+// Its cancellation boundary is synchronous: Validate does not detach schema
+// execution, and an observed context error prevents publication of a result.
 type PreparedValidation interface {
 	Validate(ctx context.Context, artifact *domain.Artifact) (domain.ValidationResult, error)
 	// SchemaDocument returns the root JSON Schema document used for provider
@@ -21,6 +26,9 @@ type PreparedValidation interface {
 }
 
 // ValidationPreparer freezes validation resources for one output contract.
+// Preparation reads schemas in context-checked chunks and checks ctx around
+// decoding and compilation. Filesystem and compiler calls remain synchronous,
+// so cancellation becomes authoritative when an in-progress call returns.
 type ValidationPreparer interface {
 	PrepareValidation(ctx context.Context, contract domain.OutputContract) (PreparedValidation, error)
 }