Add semantic configuration resume evidence

internal/manifest/semantic_fingerprint.go

@@ -0,0 +1,32 @@
+package manifest
+
+import (
+	"fmt"
+	"regexp"
+)
+
+var lowercaseSHA256Pattern = regexp.MustCompile(`^[0-9a-f]{64}$`)
+
+// SemanticConfigFingerprint identifies the versioned, result-affecting
+// configuration observed by one pipeline stage.
+type SemanticConfigFingerprint struct {
+	Version int    `json:"version"`
+	Digest  string `json:"digest"`
+}
+
+// Validate checks the durable fingerprint contract.
+func (f SemanticConfigFingerprint) Validate() error {
+	if f.Version <= 0 {
+		return fmt.Errorf("version must be positive")
+	}
+	if !lowercaseSHA256Pattern.MatchString(f.Digest) {
+		return fmt.Errorf("digest must be a lowercase SHA-256 value")
+	}
+	return nil
+}
+
+// Equal reports whether two valid fingerprint records identify the same
+// semantic configuration contract and payload.
+func (f SemanticConfigFingerprint) Equal(other SemanticConfigFingerprint) bool {
+	return f.Version == other.Version && f.Digest == other.Digest
+}