Include local backend target in checkpoint identity

internal/framework/llm/promptkit_profile_fingerprint.go

@@ -12,7 +12,9 @@ import (
 )
 
 const (
-	promptKitProfileFingerprintName = "promptkit_profile_source"
+	promptKitProfileFingerprintName      = "promptkit_profile_source"
+	promptKitLocalBackendFingerprintName = "promptkit_local_backend_target"
+	promptKitLocalBackendMarker          = "notarius:promptkit-local-backend:v1"
 	// The built-in profile catalog is compiled into this pinned PromptKit
 	// release. Update this identity when the dependency is upgraded.
 	promptKitBuiltinProfileCatalogID = "promptkit:v0.3.0:builtin-profiles"
@@ -45,6 +47,16 @@ func promptKitProfileFingerprint(profileDir, profileFile string) (CheckpointFing
 	}, nil
 }
 
+func promptKitLocalBackendFingerprint(endpoint string) CheckpointFingerprint {
+	hasher := sha256.New()
+	writeFingerprintPart(hasher, []byte(promptKitLocalBackendMarker))
+	writeFingerprintPart(hasher, []byte(strings.TrimSpace(endpoint)))
+	return CheckpointFingerprint{
+		Name:  promptKitLocalBackendFingerprintName,
+		Value: "sha256:" + hex.EncodeToString(hasher.Sum(nil)),
+	}
+}
+
 func promptKitProfileFileDigests(root string) ([][]byte, error) {
 	var digests [][]byte
 	err := filepath.WalkDir(root, func(name string, entry fs.DirEntry, walkErr error) error {