diff --git a/protocol/types.go b/protocol/types.go
index d51ff7c..992eb72 100644
--- a/protocol/types.go
+++ b/protocol/types.go
@@ -1033,6 +1033,12 @@ func (r ProviderUpstreamClientRequirement) Validate() error {
 			errs = append(errs, fmt.Errorf("%s is required", field.name))
 		}
 	}
+	if strings.TrimSpace(r.Version) != r.Version || strings.ContainsAny(r.Version, "\t\r\n\x00") {
+		errs = append(errs, errors.New("version is required"))
+	}
+	if strings.TrimSpace(r.UpstreamClientName) != r.UpstreamClientName || strings.ContainsAny(r.UpstreamClientName, "\t\r\n\x00") {
+		errs = append(errs, errors.New("upstream_client_name is required"))
+	}
 	if r.ProtocolVersion != Version {
 		errs = append(errs, fmt.Errorf("protocol_version must be %q", Version))
 	}
@@ -1048,6 +1054,21 @@ func (r ProviderUpstreamClientRequirement) Validate() error {
 	if err := r.ImagePolicy.Validate(); err != nil {
 		errs = append(errs, err)
 	}
+	for i, value := range r.VersionProbeCommand {
+		if strings.TrimSpace(value) == "" || strings.ContainsAny(value, "\t\r\n\x00") {
+			errs = append(errs, fmt.Errorf("version_probe_command[%d] is required", i))
+		}
+	}
+	for i, value := range r.RequiredEvidence {
+		if strings.TrimSpace(value) == "" || strings.ContainsAny(value, "\t\r\n\x00") {
+			errs = append(errs, fmt.Errorf("required_evidence[%d] is required", i))
+		}
+	}
+	for i, value := range r.Notes {
+		if strings.TrimSpace(value) == "" || strings.ContainsAny(value, "\t\r\n\x00") {
+			errs = append(errs, fmt.Errorf("notes[%d] is required", i))
+		}
+	}
 	return errors.Join(errs...)
 }
 
diff --git a/protocol/types_test.go b/protocol/types_test.go
index b8c01fa..df12bf6 100644
--- a/protocol/types_test.go
+++ b/protocol/types_test.go
@@ -47,6 +47,48 @@ func TestProviderUpstreamImagePolicyRequiresRecommendedImageUnlessOperatorSuppli
 	}
 }
 
+func TestProviderUpstreamClientRequirementRejectsControlWhitespaceLists(t *testing.T) {
+	req := protocol.ProviderUpstreamClientRequirement{
+		ProtocolVersion:       protocol.Version,
+		PluginID:              "workflow-plugin-crypto",
+		ProviderID:            "ethereum-full-node",
+		ContractID:            "ethereum-full-node.v1",
+		Version:               "v1.0.0",
+		RuntimeProfileID:      "sandboxed-container-runtime",
+		ConformanceProfile:    "upstream-client-v1",
+		DefaultConformance:    protocol.UpstreamClientConformanceShapeOnly,
+		RealClientConformance: protocol.UpstreamClientConformanceRealClient,
+		UpstreamClientName:    "geth",
+		VersionProbeCommand:   []string{"geth version"},
+		ImagePolicy: protocol.ProviderUpstreamImagePolicy{
+			DigestPinnedImageRequired: true,
+			RecommendedImageRef:       "ethereum/client-go@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+		},
+		RequiredEvidence: []string{"artifact://provider/evidence"},
+		Notes:            []string{"operator may provide a digest-pinned image"},
+	}
+	if err := req.Validate(); err != nil {
+		t.Fatalf("requirement invalid: %v", err)
+	}
+
+	req.VersionProbeCommand = []string{"geth\nversion"}
+	if err := req.Validate(); err == nil || !strings.Contains(err.Error(), "version_probe_command") {
+		t.Fatalf("expected version_probe_command error, got %v", err)
+	}
+	req.VersionProbeCommand = []string{"geth version"}
+
+	req.RequiredEvidence = []string{""}
+	if err := req.Validate(); err == nil || !strings.Contains(err.Error(), "required_evidence") {
+		t.Fatalf("expected required_evidence error, got %v", err)
+	}
+	req.RequiredEvidence = []string{"artifact://provider/evidence"}
+
+	req.Notes = []string{" "}
+	if err := req.Validate(); err == nil || !strings.Contains(err.Error(), "notes") {
+		t.Fatalf("expected notes error, got %v", err)
+	}
+}
+
 func TestProviderRuntimeProfileRejectsReusableResidueWithoutWorkspace(t *testing.T) {
 	contract := validBatchProviderContract()
 	profile := &contract.RuntimeContract.Profiles[0]