diff --git a/assembled_workflow_benchmark_test.go b/assembled_workflow_benchmark_test.go
index 27901c9..acbca8a 100644
--- a/assembled_workflow_benchmark_test.go
+++ b/assembled_workflow_benchmark_test.go
@@ -128,7 +128,7 @@ func verifyAssembledWorkflowFixture(b *testing.B, fixture assembledWorkflowFixtu
 	if err != nil {
 		b.Fatal(err)
 	}
-	if prepared.PromptID != "workflow" || prepared.PromptVersion != "v1" || len(prepared.Messages) != 1 ||
+	if prepared.PromptID != "workflow" || prepared.PromptVersion == nil || *prepared.PromptVersion != "v1" || len(prepared.Messages) != 1 ||
 		prepared.Messages[0].Content != fixture.expectedMessage {
 		b.Fatalf("prepared fixture output is invalid: %+v", prepared)
 	}
diff --git a/convert.go b/convert.go
index 3d7cb70..779f74e 100644
--- a/convert.go
+++ b/convert.go
@@ -72,7 +72,7 @@ func fromDomainPreparedRun(prepared *domain.PreparedRun) *PreparedRun {
 	}
 	return &PreparedRun{
 		PromptID:             prepared.PromptID,
-		PromptVersion:        prepared.PromptVersion,
+		PromptVersion:        copyStringPtr(prepared.PromptVersion),
 		PromptHash:           prepared.PromptHash,
 		SelectedProfileID:    prepared.SelectedProfileID,
 		SelectedBackendID:    prepared.SelectedBackendID,
@@ -99,7 +99,7 @@ func fromDomainRunResult(result *domain.RunResult) *RunResult {
 		RawOutput:            result.RawOutput,
 		Validation:           fromDomainValidationResult(result.Validation),
 		PromptID:             result.PromptID,
-		PromptVersion:        result.PromptVersion,
+		PromptVersion:        copyStringPtr(result.PromptVersion),
 		PromptHash:           result.PromptHash,
 		SessionID:            result.SessionID,
 		RenderedPromptHash:   result.RenderedPromptHash,
@@ -257,7 +257,7 @@ func fromDomainPromptInspection(inspection *domain.PromptInspection) *PromptInsp
 	}
 	return &PromptInspection{
 		PromptID:         inspection.PromptID,
-		PromptVersion:    inspection.PromptVersion,
+		PromptVersion:    copyStringPtr(inspection.PromptVersion),
 		PromptHash:       inspection.PromptHash,
 		DefaultProfileID: inspection.DefaultProfileID,
 		Inputs:           inputs,
diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 05e3aea..9726933 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -444,6 +444,14 @@ Validation: domain, promptdef, configuration, observation, usecase, and root tes
 `GOWORK=off go test ./...` and the offline examples. Verify the existing selected
 definition hash still agrees between inspection and preparation.
 
+Completion: prompt labels are presence-aware from configuration capture through
+inspection, listing, requirements, prepared and completed runs, observation
+events, and smoke targets. Nil and declared-empty labels remain distinct in JSON;
+null overlays clear inherited labels. Returned label pointers are independently
+owned, and inspection/preparation retain matching definition hashes. Validation
+passed: `GOWORK=off go test ./...`, `GOWORK=off go vet ./...`,
+`GOWORK=off python3 scripts/check-examples.py`, and `git diff --check`.
+
 ## Stage 7: Enable Shared Specification Checking
 
 Scope: root declaration policy through ConfigKit's released version API.
diff --git a/examples/go-library/prepare/main.go b/examples/go-library/prepare/main.go
index d596c46..1e81c8c 100644
--- a/examples/go-library/prepare/main.go
+++ b/examples/go-library/prepare/main.go
@@ -11,11 +11,11 @@ import (
 )
 
 type summary struct {
-	PromptID        string `json:"prompt_id"`
-	PromptVersion   string `json:"prompt_version"`
-	SelectedProfile string `json:"selected_profile"`
-	Model           string `json:"model"`
-	MessageCount    int    `json:"message_count"`
+	PromptID        string  `json:"prompt_id"`
+	PromptVersion   *string `json:"prompt_version,omitempty"`
+	SelectedProfile string  `json:"selected_profile"`
+	Model           string  `json:"model"`
+	MessageCount    int     `json:"message_count"`
 }
 
 func main() {
diff --git a/internal/configuration/benchmark_test.go b/internal/configuration/benchmark_test.go
index 0d17660..48238f6 100644
--- a/internal/configuration/benchmark_test.go
+++ b/internal/configuration/benchmark_test.go
@@ -228,7 +228,7 @@ func BenchmarkInspectionSelection(b *testing.B) {
 		}
 		ctx := context.Background()
 		definition, hash, err := result.GetPromptSnapshot(ctx, "inspection")
-		if err != nil || definition.ID != "inspection" || definition.Version != "1" || hash == "" ||
+		if err != nil || definition.ID != "inspection" || definition.Version == nil || *definition.Version != "1" || hash == "" ||
 			len(definition.Inputs) != 1 || definition.Inputs[0].Name != "transcript" || !definition.Inputs[0].Required {
 			b.Fatalf("prompt lookup fixture is invalid: definition=%+v hash=%q err=%v", definition, hash, err)
 		}
@@ -238,7 +238,7 @@ func BenchmarkInspectionSelection(b *testing.B) {
 			b.Fatalf("profile lookup fixture is invalid: profile=%+v err=%v", profile, err)
 		}
 		inspection, err := result.GetPromptInspection(ctx, "inspection")
-		if err != nil || inspection.PromptID != "inspection" || inspection.PromptVersion != "1" ||
+		if err != nil || inspection.PromptID != "inspection" || inspection.PromptVersion == nil || *inspection.PromptVersion != "1" ||
 			len(inspection.Inputs) != 1 || inspection.Inputs[0].Name != "transcript" {
 			b.Fatalf("prompt inspection fixture is invalid: inspection=%+v err=%v", inspection, err)
 		}
diff --git a/internal/configuration/listing.go b/internal/configuration/listing.go
index 32776d1..3cd8b7d 100644
--- a/internal/configuration/listing.go
+++ b/internal/configuration/listing.go
@@ -22,6 +22,9 @@ func (state *loaded) ListPrompts(ctx context.Context) ([]domain.PromptIdentity,
 		return nil, err
 	}
 	prompts := append([]domain.PromptIdentity(nil), state.promptIDs...)
+	for index := range prompts {
+		prompts[index].Version = stringPointerValue(prompts[index].Version)
+	}
 	if err := ctx.Err(); err != nil {
 		return nil, err
 	}
diff --git a/internal/configuration/listing_test.go b/internal/configuration/listing_test.go
index 8cb4851..3e5cf7b 100644
--- a/internal/configuration/listing_test.go
+++ b/internal/configuration/listing_test.go
@@ -45,9 +45,9 @@ func TestLoadedListsSortedEffectiveIdentities(t *testing.T) {
 		t.Fatal(err)
 	}
 	wantPrompts := []domain.PromptIdentity{
-		{ID: " z/prompt ", Version: "v1"},
-		{ID: "a/prompt", Version: "v1"},
-		{ID: "z/prompt", Version: "v1"},
+		{ID: " z/prompt ", Version: stringPointer("v1")},
+		{ID: "a/prompt", Version: stringPointer("v1")},
+		{ID: "z/prompt", Version: stringPointer("v1")},
 	}
 	if !reflect.DeepEqual(prompts, wantPrompts) {
 		t.Fatalf("prompt identities = %#v, want %#v", prompts, wantPrompts)
@@ -75,7 +75,7 @@ func TestLoadedListsAreIndependent(t *testing.T) {
 		t.Fatal(err)
 	}
 	prompts[0].ID = "changed prompt"
-	prompts[0].Version = "changed version"
+	*prompts[0].Version = "changed version"
 
 	profiles, err = state.ListProfiles(context.Background())
 	if err != nil {
@@ -88,7 +88,7 @@ func TestLoadedListsAreIndependent(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	wantPrompts := []domain.PromptIdentity{{ID: "example", Version: "v1"}}
+	wantPrompts := []domain.PromptIdentity{{ID: "example", Version: stringPointer("v1")}}
 	if !reflect.DeepEqual(prompts, wantPrompts) {
 		t.Fatalf("caller mutation changed prompt inventory: %#v", prompts)
 	}
diff --git a/internal/configuration/load.go b/internal/configuration/load.go
index f6c2cf4..481ab39 100644
--- a/internal/configuration/load.go
+++ b/internal/configuration/load.go
@@ -181,7 +181,7 @@ func load(main configkit.Input, underlays []configkit.Underlay) (*loaded, error)
 	}
 	state.profileIDs = sortedKeys(state.indexedProfiles)
 	for _, id := range sortedKeys(state.prompts) {
-		state.promptIDs = append(state.promptIDs, domain.PromptIdentity{ID: id, Version: state.prompts[id].definition.Version})
+		state.promptIDs = append(state.promptIDs, domain.PromptIdentity{ID: id, Version: stringPointerValue(state.prompts[id].definition.Version)})
 	}
 	return state, nil
 }
diff --git a/internal/configuration/prompts.go b/internal/configuration/prompts.go
index cc7382c..0ff01e2 100644
--- a/internal/configuration/prompts.go
+++ b/internal/configuration/prompts.go
@@ -96,11 +96,7 @@ func (state *loaded) materializePrompts(prompts map[string]promptConfig, basePat
 		if strings.TrimSpace(id) == "" {
 			return fmt.Errorf("%s: prompt ID must not be blank", promptBase)
 		}
-		version := ""
-		if prompts[id].Version != nil {
-			version = *prompts[id].Version
-		}
-		entry, err := state.materializePrompt(id, version, prompts[id], promptBase, lookupOrigin)
+		entry, err := state.materializePrompt(id, prompts[id].Version, prompts[id], promptBase, lookupOrigin)
 		if err != nil {
 			return err
 		}
@@ -109,11 +105,11 @@ func (state *loaded) materializePrompts(prompts map[string]promptConfig, basePat
 	return nil
 }
 
-func (state *loaded) materializePrompt(id, version string, raw promptConfig, base configkit.Path, lookupOrigin func(configkit.Path) (configkit.FieldInfo, bool)) (*promptEntry, error) {
+func (state *loaded) materializePrompt(id string, version *string, raw promptConfig, base configkit.Path, lookupOrigin func(configkit.Path) (configkit.FieldInfo, bool)) (*promptEntry, error) {
 	if len(raw.Messages) == 0 {
 		return nil, fmt.Errorf("%s: at least one message is required", base.Key("messages"))
 	}
-	definition := domain.PromptDefinition{ID: id, Version: version}
+	definition := domain.PromptDefinition{ID: id, Version: stringPointerValue(version)}
 	if raw.DefaultProfile != nil {
 		if strings.TrimSpace(*raw.DefaultProfile) == "" {
 			return nil, fmt.Errorf("%s: default profile must not be blank", base.Key("default_profile"))
@@ -242,7 +238,7 @@ func (state *loaded) materializePrompt(id, version string, raw promptConfig, bas
 	entry.definition = definition
 	entry.hash = hash
 	entry.inspection = domain.PromptInspection{
-		PromptID: id, PromptVersion: version, PromptHash: hash,
+		PromptID: id, PromptVersion: stringPointerValue(version), PromptHash: hash,
 		DefaultProfileID: definition.DefaultProfile, Inputs: append([]domain.PromptInput(nil), definition.Inputs...),
 		OutputContract: contract,
 	}
@@ -254,6 +250,13 @@ func stringPointer(value string) *string {
 	return &copy
 }
 
+func stringPointerValue(value *string) *string {
+	if value == nil {
+		return nil
+	}
+	return stringPointer(*value)
+}
+
 func (state *loaded) readContent(fieldPath configkit.Path, name string, lookupOrigin func(configkit.Path) (configkit.FieldInfo, bool)) (string, error) {
 	if strings.TrimSpace(name) == "" {
 		return "", fmt.Errorf("%s: content_file path must not be blank", fieldPath)
@@ -298,6 +301,7 @@ func (state *loaded) lookupPromptEntry(id string) (*promptEntry, error) {
 }
 
 func ownPromptDefinition(definition domain.PromptDefinition) *domain.PromptDefinition {
+	definition.Version = stringPointerValue(definition.Version)
 	definition.Inputs = append([]domain.PromptInput(nil), definition.Inputs...)
 	definition.Templates = append([]domain.PromptMessageTemplate(nil), definition.Templates...)
 	for index := range definition.Templates {
@@ -310,6 +314,7 @@ func ownPromptDefinition(definition domain.PromptDefinition) *domain.PromptDefin
 }
 
 func ownPromptInspection(inspection domain.PromptInspection) *domain.PromptInspection {
+	inspection.PromptVersion = stringPointerValue(inspection.PromptVersion)
 	inspection.Inputs = append([]domain.PromptInput(nil), inspection.Inputs...)
 	return &inspection
 }
diff --git a/internal/configuration/prompts_test.go b/internal/configuration/prompts_test.go
index 2ded508..1820163 100644
--- a/internal/configuration/prompts_test.go
+++ b/internal/configuration/prompts_test.go
@@ -131,11 +131,112 @@ func TestLoadRejectsMalformedStaticSyntaxAndCapturesOptionalVersion(t *testing.T
 		t.Fatal(err)
 	}
 	definition, inspection, err := state.prompt("example")
-	if err != nil || definition.Version != "release label" || inspection.PromptVersion != "release label" {
+	if err != nil || definition.Version == nil || *definition.Version != "release label" ||
+		inspection.PromptVersion == nil || *inspection.PromptVersion != "release label" {
 		t.Fatalf("optional version metadata was not retained: definition=%+v inspection=%+v err=%v", definition, inspection, err)
 	}
 }
 
+func TestPromptVersionLabelPresenceAndOwnership(t *testing.T) {
+	tests := []struct {
+		name        string
+		version     any
+		include     bool
+		wantPresent bool
+		wantValue   string
+	}{
+		{name: "absent"},
+		{name: "null", include: true},
+		{name: "empty", version: "", include: true, wantPresent: true},
+		{name: "exact text", version: " Release/v1 ", include: true, wantPresent: true, wantValue: " Release/v1 "},
+	}
+
+	hashes := make(map[string]string, len(tests))
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			definition := map[string]any{
+				"messages": []any{map[string]any{"role": "user", "content": "hello"}},
+				"output":   map[string]any{"format": "text", "validation_mode": "basic"},
+			}
+			if test.include {
+				definition["version"] = test.version
+			}
+			state, err := load(mapping("prompt version label", map[string]any{
+				"prompts": map[string]any{"example": definition},
+			}), nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			captured, inspection, err := state.prompt("example")
+			if err != nil {
+				t.Fatal(err)
+			}
+			identities, err := state.ListPrompts(context.Background())
+			if err != nil || len(identities) != 1 {
+				t.Fatalf("list prompt labels: %#v, %v", identities, err)
+			}
+			check := func(name string, value *string) {
+				t.Helper()
+				if !test.wantPresent {
+					if value != nil {
+						t.Errorf("%s label = %q, want absent", name, *value)
+					}
+					return
+				}
+				if value == nil || *value != test.wantValue {
+					t.Errorf("%s label = %v, want %q", name, value, test.wantValue)
+				}
+			}
+			check("definition", captured.Version)
+			check("inspection", inspection.PromptVersion)
+			check("listing", identities[0].Version)
+			if captured.Version != nil && (captured.Version == inspection.PromptVersion || captured.Version == identities[0].Version || inspection.PromptVersion == identities[0].Version) {
+				t.Fatal("returned prompt labels share mutable pointers")
+			}
+			hashes[test.name] = inspection.PromptHash
+
+			if captured.Version != nil {
+				*captured.Version = "mutated definition"
+			}
+			if inspection.PromptVersion != nil {
+				*inspection.PromptVersion = "mutated inspection"
+			}
+			if identities[0].Version != nil {
+				*identities[0].Version = "mutated listing"
+			}
+			again, againInspection, err := state.prompt("example")
+			if err != nil {
+				t.Fatal(err)
+			}
+			check("captured definition after mutation", again.Version)
+			check("captured inspection after mutation", againInspection.PromptVersion)
+		})
+	}
+	if hashes["absent"] == hashes["empty"] {
+		t.Fatal("absent and declared-empty labels produced the same definition hash")
+	}
+}
+
+func TestPromptVersionNullClearsInheritedLabel(t *testing.T) {
+	prompt := map[string]any{
+		"version":  "base-label",
+		"messages": []any{map[string]any{"role": "user", "content": "hello"}},
+		"output":   map[string]any{"format": "text", "validation_mode": "basic"},
+	}
+	state, err := load(
+		mapping("clear inherited label", map[string]any{"prompts": map[string]any{"example": map[string]any{"version": nil}}}),
+		[]configkit.Underlay{{Inputs: []configkit.Input{mapping("base prompt", map[string]any{"prompts": map[string]any{"example": prompt}})}}},
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+	definition, inspection, err := state.prompt("example")
+	if err != nil || definition.Version != nil || inspection.PromptVersion != nil {
+		t.Fatalf("null overlay retained inherited label: definition=%+v inspection=%+v err=%v", definition, inspection, err)
+	}
+}
+
 func TestPromptInspectionLookupMatchesSnapshotSelectionAndOwnsInputs(t *testing.T) {
 	makePrompt := func(content string) map[string]any {
 		return map[string]any{
@@ -169,7 +270,8 @@ func TestPromptInspectionLookupMatchesSnapshotSelectionAndOwnsInputs(t *testing.
 		if err != nil {
 			t.Fatalf("snapshot prompt ID: %v", err)
 		}
-		if inspection.PromptID != definition.ID || inspection.PromptVersion != definition.Version ||
+		if inspection.PromptID != definition.ID || inspection.PromptVersion == nil || definition.Version == nil ||
+			*inspection.PromptVersion != *definition.Version ||
 			inspection.PromptHash != hash || inspection.DefaultProfileID != "partial" ||
 			len(inspection.Inputs) != 1 || inspection.Inputs[0].Name != "document" ||
 			inspection.Inputs[0].ContentType != "text/plain" || inspection.Inputs[0].Description != "source document" {
diff --git a/internal/domain/domain.go b/internal/domain/domain.go
index 1cc5796..de6b552 100644
--- a/internal/domain/domain.go
+++ b/internal/domain/domain.go
@@ -80,7 +80,7 @@ type RunResult struct {
 	RawOutput            string
 	Validation           ValidationResult
 	PromptID             string
-	PromptVersion        string
+	PromptVersion        *string
 	PromptHash           string
 	SessionID            string
 	RenderedPromptHash   string
@@ -100,7 +100,7 @@ type RunResult struct {
 // It must never include resolved API key values, model output, or validation data.
 type PreparedRun struct {
 	PromptID             string
-	PromptVersion        string
+	PromptVersion        *string
 	PromptHash           string
 	SelectedProfileID    string
 	SelectedBackendID    string
@@ -137,13 +137,13 @@ type Artifact struct {
 // PromptIdentity identifies one configured prompt and its descriptive version label.
 type PromptIdentity struct {
 	ID      string
-	Version string
+	Version *string
 }
 
 // PromptDefinition represents a configured prompt execution definition.
 type PromptDefinition struct {
 	ID             string                  `yaml:"id"`
-	Version        string                  `yaml:"version"`
+	Version        *string                 `yaml:"version"`
 	DefaultProfile string                  `yaml:"default_profile"`
 	Description    string                  `yaml:"description"`
 	SessionID      string                  `yaml:"session_id" json:"session_id,omitempty"`
@@ -156,7 +156,7 @@ type PromptDefinition struct {
 // PromptInspection is the resolved result of exact prompt inspection.
 type PromptInspection struct {
 	PromptID         string
-	PromptVersion    string
+	PromptVersion    *string
 	PromptHash       string
 	DefaultProfileID string
 	Inputs           []PromptInput
diff --git a/internal/domain/observation.go b/internal/domain/observation.go
index a9df6f0..054b507 100644
--- a/internal/domain/observation.go
+++ b/internal/domain/observation.go
@@ -68,7 +68,7 @@ type ExecutionEvent struct {
 	RunID              string
 	Time               time.Time
 	PromptID           string
-	PromptVersion      string
+	PromptVersion      *string
 	ProfileID          string
 	BackendID          string
 	Model              string
diff --git a/internal/domain/requirements.go b/internal/domain/requirements.go
index 9d981e9..288440c 100644
--- a/internal/domain/requirements.go
+++ b/internal/domain/requirements.go
@@ -49,7 +49,7 @@ type RequirementIssue struct {
 // RequirementInspection contains the inventories discovered for one prompt.
 type RequirementInspection struct {
 	PromptID      string
-	PromptVersion string
+	PromptVersion *string
 	ProfileID     string
 	Inputs        []InputRequirement
 	Variables     []VariableRequirement
diff --git a/internal/domain/smoke_diagnostics.go b/internal/domain/smoke_diagnostics.go
index 6ee608d..d2056c5 100644
--- a/internal/domain/smoke_diagnostics.go
+++ b/internal/domain/smoke_diagnostics.go
@@ -65,7 +65,7 @@ type SmokeTestTarget struct {
 	BackendID              string
 	ProfileID              string
 	PromptID               string
-	PromptVersion          string
+	PromptVersion          *string
 	DefaultSourceBackendID string
 	SelectionSource        string
 	Endpoint               string
@@ -180,6 +180,7 @@ func CloneSmokeTestRequest(request SmokeTestRequest) (SmokeTestRequest, error) {
 func CloneSmokeTestReport(report SmokeTestReport) (SmokeTestReport, error) {
 	cloned := report
 	cloned.Applicable = cloneBool(report.Applicable)
+	cloned.Target.PromptVersion = cloneString(report.Target.PromptVersion)
 	cloned.Facts = cloneSmokeTestFacts(report.Facts)
 	cloned.Timing = cloneSmokeTestTiming(report.Timing)
 	var err error
diff --git a/internal/domain/smoke_diagnostics_test.go b/internal/domain/smoke_diagnostics_test.go
index ea87df9..a6abc72 100644
--- a/internal/domain/smoke_diagnostics_test.go
+++ b/internal/domain/smoke_diagnostics_test.go
@@ -77,11 +77,15 @@ func TestCloneSmokeTestReportOwnsMutableValues(t *testing.T) {
 	reachable := true
 	status := 200
 	wait := 3 * time.Millisecond
+	promptVersion := "v1"
 	report := SmokeTestReport{
 		Applicable: &applicable,
-		Target: SmokeTestTarget{EffectiveSettings: ExecutionTarget{
-			ExtraParams: map[string]any{"nested": map[string]any{"value": "original"}},
-		}},
+		Target: SmokeTestTarget{
+			PromptVersion: &promptVersion,
+			EffectiveSettings: ExecutionTarget{
+				ExtraParams: map[string]any{"nested": map[string]any{"value": "original"}},
+			},
+		},
 		Facts: SmokeTestFacts{EndpointReachable: &reachable},
 		Attempts: []SmokeTestAttempt{{
 			HTTPStatus: &status,
@@ -99,9 +103,10 @@ func TestCloneSmokeTestReportOwnsMutableValues(t *testing.T) {
 	*cloned.Attempts[0].HTTPStatus = 503
 	*cloned.Attempts[0].Facts.EndpointReachable = false
 	*cloned.Attempts[0].Timing.CapacityWait = time.Second
+	*cloned.Target.PromptVersion = "changed"
 	cloned.Target.EffectiveSettings.ExtraParams["nested"].(map[string]any)["value"] = "changed"
 
-	if !applicable || !reachable || status != 200 || wait != 3*time.Millisecond {
+	if !applicable || !reachable || status != 200 || wait != 3*time.Millisecond || promptVersion != "v1" {
 		t.Fatal("cloned report shared optional scalar pointers")
 	}
 	if got := report.Target.EffectiveSettings.ExtraParams["nested"].(map[string]any)["value"]; got != "original" {
diff --git a/internal/observation/recorder.go b/internal/observation/recorder.go
index 3a30365..7302264 100644
--- a/internal/observation/recorder.go
+++ b/internal/observation/recorder.go
@@ -34,7 +34,7 @@ type Recorder struct {
 // Selection contains resolved identities only. Unresolved fields stay empty.
 type Selection struct {
 	PromptID      string
-	PromptVersion string
+	PromptVersion *string
 	ProfileID     string
 	BackendID     string
 	Model         string
@@ -103,7 +103,10 @@ func (r *Recorder) Start() {
 }
 
 // UpdateSelection replaces the known resolved identities for later events.
-func (r *Recorder) UpdateSelection(selection Selection) { r.selection = selection }
+func (r *Recorder) UpdateSelection(selection Selection) {
+	selection.PromptVersion = copyStringPointer(selection.PromptVersion)
+	r.selection = selection
+}
 
 // Attempt records one completed acquisition and optional dispatch.
 func (r *Recorder) Attempt(data AttemptData) {
@@ -177,11 +180,19 @@ func (r *Recorder) Finish(data FinishData) {
 func (r *Recorder) event(kind domain.ExecutionEventKind) domain.ExecutionEvent {
 	return domain.ExecutionEvent{
 		Kind: kind, RunID: r.runID, Time: r.now(), PromptID: r.selection.PromptID,
-		PromptVersion: r.selection.PromptVersion, ProfileID: r.selection.ProfileID,
+		PromptVersion: copyStringPointer(r.selection.PromptVersion), ProfileID: r.selection.ProfileID,
 		BackendID: r.selection.BackendID, Model: r.selection.Model,
 	}
 }
 
+func copyStringPointer(value *string) *string {
+	if value == nil {
+		return nil
+	}
+	copy := *value
+	return &copy
+}
+
 func (r *Recorder) deliver(event domain.ExecutionEvent) {
 	if r.observer != nil {
 		r.observer(event)
diff --git a/internal/observation/recorder_test.go b/internal/observation/recorder_test.go
index ac34777..b30813b 100644
--- a/internal/observation/recorder_test.go
+++ b/internal/observation/recorder_test.go
@@ -50,7 +50,8 @@ func TestRecorderAccountsDispatchedAttemptsAndReportedUsage(t *testing.T) {
 	var events []domain.ExecutionEvent
 	recorder := newRecorder("run-1", now, func(event domain.ExecutionEvent) { events = append(events, event) })
 	recorder.Start()
-	recorder.UpdateSelection(Selection{PromptID: "prompt", PromptVersion: "v1", ProfileID: "profile", BackendID: "backend", Model: "model"})
+	version := "v1"
+	recorder.UpdateSelection(Selection{PromptID: "prompt", PromptVersion: &version, ProfileID: "profile", BackendID: "backend", Model: "model"})
 	recorder.Attempt(AttemptData{
 		Generation: 1, Attempt: 1, Dispatched: true,
 		CapacityWait: 2 * time.Millisecond, GenerationDuration: 10 * time.Millisecond,
diff --git a/internal/prompt/compiled_renderer_benchmark_test.go b/internal/prompt/compiled_renderer_benchmark_test.go
index 0ea2605..c7d5bde 100644
--- a/internal/prompt/compiled_renderer_benchmark_test.go
+++ b/internal/prompt/compiled_renderer_benchmark_test.go
@@ -52,7 +52,7 @@ func BenchmarkCompiledRendering(b *testing.B) {
 	small := newCompiledRenderingBenchmarkCase(b,
 		"small_message", "", []string{"Summary for {{.audience}}."},
 		&domain.PromptDefinition{
-			ID: "compiled-render-benchmark", Version: "v1",
+			ID: "compiled-render-benchmark", Version: stringPointerForTest("v1"),
 			Templates: []domain.PromptMessageTemplate{{Role: "user", Content: "Summary for {{.audience}}."}},
 		}, nil, map[string]string{"audience": "project leads"},
 		len("Summary for project leads."),
@@ -68,7 +68,7 @@ func BenchmarkCompiledRendering(b *testing.B) {
 	}
 	largeContent := `{{input "document"}}`
 	largeDefinition := &domain.PromptDefinition{
-		ID: "compiled-render-benchmark", Version: "v1",
+		ID: "compiled-render-benchmark", Version: stringPointerForTest("v1"),
 		Inputs:    []domain.PromptInput{{Name: "document"}},
 		Templates: []domain.PromptMessageTemplate{{Role: "user", Content: largeContent}},
 	}
@@ -91,7 +91,7 @@ func BenchmarkCompiledRendering(b *testing.B) {
 		`{{input "document"}}|{{input "document"}}`,
 	}
 	repeatedDefinition := &domain.PromptDefinition{
-		ID: "compiled-render-benchmark", Version: "v1", SessionID: repeatedSession,
+		ID: "compiled-render-benchmark", Version: stringPointerForTest("v1"), SessionID: repeatedSession,
 		Inputs: []domain.PromptInput{{Name: "document"}},
 		Templates: []domain.PromptMessageTemplate{
 			{Role: "system", Content: repeatedMessages[0]},
@@ -141,7 +141,7 @@ func BenchmarkRetainedRenderedOutput(b *testing.B) {
 	bodyText := string(body)
 	content := `{{input "document"}}`
 	definition := &domain.PromptDefinition{
-		ID: "retained-render-benchmark", Version: "v1",
+		ID: "retained-render-benchmark", Version: stringPointerForTest("v1"),
 		Inputs:    []domain.PromptInput{{Name: "document"}},
 		Templates: []domain.PromptMessageTemplate{{Role: "user", Content: content}},
 	}
diff --git a/internal/prompt/renderer_test.go b/internal/prompt/renderer_test.go
index 5d24169..3acdfc5 100644
--- a/internal/prompt/renderer_test.go
+++ b/internal/prompt/renderer_test.go
@@ -525,7 +525,7 @@ func TestCompiledRendererKeepsConcurrentRequestsIndependent(t *testing.T) {
 		},
 	})
 	definition := &domain.PromptDefinition{
-		ID: promptID, Version: version, SessionID: "session-{{.request}}",
+		ID: promptID, Version: stringPointerForTest(version), SessionID: "session-{{.request}}",
 		Inputs:    []domain.PromptInput{{Name: "document"}},
 		Templates: []domain.PromptMessageTemplate{{Role: "user", Content: `request={{.request}};document={{input "document"}}`}},
 	}
diff --git a/internal/prompt/requirements.go b/internal/prompt/requirements.go
index f918231..61063b0 100644
--- a/internal/prompt/requirements.go
+++ b/internal/prompt/requirements.go
@@ -384,7 +384,7 @@ func AnalyzeRequirements(
 	result := domain.RequirementInspection{Complete: true}
 	if definition != nil {
 		result.PromptID = definition.ID
-		result.PromptVersion = definition.Version
+		result.PromptVersion = copyString(definition.Version)
 	}
 	walker := &requirementWalker{
 		ctx:       ctx,
diff --git a/internal/prompt/requirements_test.go b/internal/prompt/requirements_test.go
index 77e9506..f7da7bf 100644
--- a/internal/prompt/requirements_test.go
+++ b/internal/prompt/requirements_test.go
@@ -108,7 +108,7 @@ func TestRequirementWalkerDoesNotRescanNestedUnsupportedNames(t *testing.T) {
 
 func TestAnalyzeRequirementsCollectsDeclaredAndLiteralInputs(t *testing.T) {
 	description := "retained metadata"
-	definition := &domain.PromptDefinition{ID: "capture", Version: "v1"}
+	definition := &domain.PromptDefinition{ID: "capture", Version: stringPointerForTest("v1")}
 	snapshot := RequirementSnapshot{
 		Inputs: []InputMetadata{
 			{Name: "optional", ContentType: stringPointerForTest("text/plain"), Description: &description},
@@ -123,7 +123,7 @@ func TestAnalyzeRequirementsCollectsDeclaredAndLiteralInputs(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if result.PromptID != "capture" || result.PromptVersion != "v1" || !result.Complete || len(result.Issues) != 0 {
+	if result.PromptID != "capture" || result.PromptVersion == nil || *result.PromptVersion != "v1" || !result.Complete || len(result.Issues) != 0 {
 		t.Fatalf("unexpected result identity or completeness: %+v", result)
 	}
 	wantNames := []string{"extra", "optional", "transcript", "unused"}
diff --git a/internal/usecase/prompt_inspection.go b/internal/usecase/prompt_inspection.go
index ee5d959..71b147e 100644
--- a/internal/usecase/prompt_inspection.go
+++ b/internal/usecase/prompt_inspection.go
@@ -76,7 +76,7 @@ func (r *Runner) resolvePromptInspection(ctx context.Context, promptID string) (
 	definition := selection.definition
 	return &domain.PromptInspection{
 		PromptID:         definition.ID,
-		PromptVersion:    definition.Version,
+		PromptVersion:    copyStringPointer(definition.Version),
 		PromptHash:       selection.hash,
 		DefaultProfileID: definition.DefaultProfile,
 		Inputs:           append([]domain.PromptInput(nil), definition.Inputs...),
diff --git a/internal/usecase/prompt_inspection_test.go b/internal/usecase/prompt_inspection_test.go
index 83042b3..3ed6bf0 100644
--- a/internal/usecase/prompt_inspection_test.go
+++ b/internal/usecase/prompt_inspection_test.go
@@ -52,7 +52,7 @@ func (r *promptMetadataRepository) GetPromptInspection(
 func TestRunnerInspectPromptResolvesOneDefinitionWithoutExecutionCollaborators(t *testing.T) {
 	definition := &domain.PromptDefinition{
 		ID:             "normalized.prompt",
-		Version:        "1.2.3",
+		Version:        stringPtr("1.2.3"),
 		DefaultProfile: "not-resolved",
 		Inputs: []domain.PromptInput{
 			{Name: "document", Required: true, ContentType: "text/plain", Description: "Source document."},
@@ -79,8 +79,8 @@ func TestRunnerInspectPromptResolvesOneDefinitionWithoutExecutionCollaborators(t
 	if repository.calls != 1 || repository.id != " prompt-id " {
 		t.Fatalf("prompt lookup=(calls=%d id=%q), want one unchanged ID lookup", repository.calls, repository.id)
 	}
-	if inspection.PromptID != definition.ID ||
-		inspection.PromptVersion != definition.Version ||
+	if inspection.PromptID != definition.ID || inspection.PromptVersion == nil || definition.Version == nil ||
+		*inspection.PromptVersion != *definition.Version ||
 		inspection.PromptHash != wantHash ||
 		inspection.DefaultProfileID != definition.DefaultProfile ||
 		!reflect.DeepEqual(inspection.Inputs, definition.Inputs) ||
@@ -100,7 +100,7 @@ func TestRunnerInspectPromptResolvesOneDefinitionWithoutExecutionCollaborators(t
 
 func TestRunnerInspectPromptUsesOwnedMetadataWhenRepositorySupportsIt(t *testing.T) {
 	repository := &promptMetadataRepository{inspection: domain.PromptInspection{
-		PromptID: "captured.prompt", PromptVersion: "v2", PromptHash: "cached-prompt-hash",
+		PromptID: "captured.prompt", PromptVersion: stringPtr("v2"), PromptHash: "cached-prompt-hash",
 		DefaultProfileID: "partial-profile",
 		Inputs:           []domain.PromptInput{{Name: "document", Required: true, ContentType: "text/plain", Description: "Captured."}},
 		OutputContract:   domain.OutputContract{Format: domain.FormatJSON, ValidationMode: domain.ValidationJSON},
@@ -108,7 +108,7 @@ func TestRunnerInspectPromptUsesOwnedMetadataWhenRepositorySupportsIt(t *testing
 	runner := &Runner{promptDefs: repository}
 	inspection, err := runner.InspectPrompt(context.Background(), " requested-id ")
 	if err != nil || repository.lookupID != " requested-id " ||
-		inspection.PromptID != "captured.prompt" || inspection.PromptVersion != "v2" ||
+		inspection.PromptID != "captured.prompt" || inspection.PromptVersion == nil || *inspection.PromptVersion != "v2" ||
 		inspection.PromptHash != "cached-prompt-hash" || inspection.DefaultProfileID != "partial-profile" ||
 		!reflect.DeepEqual(inspection.Inputs, repository.inspection.Inputs) || inspection.OutputContract != repository.inspection.OutputContract {
 		t.Fatalf("metadata inspection=(%+v, %v), lookup=%q", inspection, err, repository.lookupID)
@@ -124,11 +124,11 @@ func TestRunnerInspectPromptUsesOwnedMetadataWhenRepositorySupportsIt(t *testing
 func TestRunnerInspectPromptUsesCapturedHashWhenMetadataCapabilityIsAbsent(t *testing.T) {
 	repository := &requirementInspectionPromptRepository{
 		definition: &domain.PromptDefinition{
-			ID: "captured.prompt", Version: "v1", Inputs: []domain.PromptInput{{Name: "document"}},
+			ID: "captured.prompt", Version: stringPtr("v1"), Inputs: []domain.PromptInput{{Name: "document"}},
 		},
 	}
 	inspection, err := (&Runner{promptDefs: repository}).InspectPrompt(context.Background(), " requested-id ")
-	if err != nil || inspection.PromptID != "captured.prompt" || inspection.PromptVersion != "v1" ||
+	if err != nil || inspection.PromptID != "captured.prompt" || inspection.PromptVersion == nil || *inspection.PromptVersion != "v1" ||
 		inspection.PromptHash != "captured-hash" || inspection.Inputs[0].Name != "document" {
 		t.Fatalf("captured-hash fallback inspection=(%+v, %v)", inspection, err)
 	}
diff --git a/internal/usecase/requirements_inspection.go b/internal/usecase/requirements_inspection.go
index 32e81a0..b713dcb 100644
--- a/internal/usecase/requirements_inspection.go
+++ b/internal/usecase/requirements_inspection.go
@@ -69,7 +69,7 @@ func (r *Runner) InspectRequirements(
 	if !ok {
 		return nil, fmt.Errorf("%w: captured requirement snapshot is unavailable", ErrPromptLoad)
 	}
-	definition := &domain.PromptDefinition{ID: selection.PromptID, Version: selection.PromptVersion}
+	definition := &domain.PromptDefinition{ID: selection.PromptID, Version: copyStringPointer(selection.PromptVersion)}
 	inspection, err := prompt.AnalyzeRequirements(ctx, definition, snapshot, req.Vars, directSessionID != "")
 	if err != nil {
 		return nil, fmt.Errorf("%w: %w", ErrPromptLoad, err)
diff --git a/internal/usecase/requirements_inspection_test.go b/internal/usecase/requirements_inspection_test.go
index c9299e6..8a58046 100644
--- a/internal/usecase/requirements_inspection_test.go
+++ b/internal/usecase/requirements_inspection_test.go
@@ -88,7 +88,7 @@ func TestRunnerInspectRequirementsUsesCapturedSelectionWithoutExecutionWork(t *t
 	if err != nil {
 		t.Fatal(err)
 	}
-	definition := &domain.PromptDefinition{ID: "selected", Version: "v2", DefaultProfile: "default-profile"}
+	definition := &domain.PromptDefinition{ID: "selected", Version: stringPtr("v2"), DefaultProfile: "default-profile"}
 	repository := &requirementInspectionPromptRepository{
 		definition:    definition,
 		snapshotFound: true,
@@ -113,7 +113,7 @@ func TestRunnerInspectRequirementsUsesCapturedSelectionWithoutExecutionWork(t *t
 			repository.snapshotCalls, repository.snapshotID)
 	}
 	if profiles.calls != 1 || profiles.id != "partial-profile" || inspection.PromptID != definition.ID ||
-		inspection.PromptVersion != definition.Version || inspection.ProfileID != "partial-profile" || !inspection.Complete ||
+		inspection.PromptVersion == nil || *inspection.PromptVersion != *definition.Version || inspection.ProfileID != "partial-profile" || !inspection.Complete ||
 		len(inspection.Inputs) != 1 || inspection.Inputs[0].Name != "message-input" || len(inspection.Variables) != 1 ||
 		inspection.Variables[0].Name != "caller" || !inspection.Variables[0].Supplied {
 		t.Fatalf("unexpected requirement inspection: %+v", inspection)
@@ -138,7 +138,7 @@ func TestRunnerInspectRequirementsUsesPromptMetadataAndExactRequirementSnapshot(
 	promptRepository := &requirementPromptMetadataRepository{
 		requirementInspectionPromptRepository: baseRepository,
 		inspection: domain.PromptInspection{
-			PromptID: "captured-id", PromptVersion: "captured-version", PromptHash: "captured-hash",
+			PromptID: "captured-id", PromptVersion: stringPtr("captured-version"), PromptHash: "captured-hash",
 			DefaultProfileID: "default-profile",
 		},
 	}
@@ -155,7 +155,7 @@ func TestRunnerInspectRequirementsUsesPromptMetadataAndExactRequirementSnapshot(
 	if err != nil || promptRepository.lookupID != " requested-id " ||
 		baseRepository.snapshotID != "captured-id" ||
 		profiles.identityID != "default-profile" || inspection.PromptID != "captured-id" ||
-		inspection.PromptVersion != "captured-version" || inspection.ProfileID != "default-profile" ||
+		inspection.PromptVersion == nil || *inspection.PromptVersion != "captured-version" || inspection.ProfileID != "default-profile" ||
 		!inspection.Complete || len(inspection.Inputs) != 1 || inspection.Inputs[0].Name != "message-input" ||
 		len(inspection.Variables) != 1 || inspection.Variables[0].Name != "caller" || !inspection.Variables[0].Supplied {
 		t.Fatalf("metadata-based requirement inspection=(%+v, %v), prompt lookup=%q, snapshot=%q, profile=%q",
@@ -168,7 +168,7 @@ func TestRunnerInspectRequirementsUsesProfileIdentityCapabilityOrFallback(t *tes
 	if err != nil {
 		t.Fatal(err)
 	}
-	definition := &domain.PromptDefinition{ID: "selected", Version: "v1"}
+	definition := &domain.PromptDefinition{ID: "selected", Version: stringPtr("v1")}
 	makePromptRepository := func() *requirementInspectionPromptRepository {
 		return &requirementInspectionPromptRepository{
 			definition: definition, snapshotFound: true,
@@ -234,7 +234,7 @@ func TestRunnerInspectRequirementsUsesPromptDefaultAndIncludesSessionWhenNotBypa
 	if err != nil {
 		t.Fatal(err)
 	}
-	definition := &domain.PromptDefinition{ID: "selected", Version: "v1", DefaultProfile: "default-profile"}
+	definition := &domain.PromptDefinition{ID: "selected", Version: stringPtr("v1"), DefaultProfile: "default-profile"}
 	repository := &requirementInspectionPromptRepository{
 		definition: definition, snapshotFound: true,
 		snapshot: prompt.RequirementSnapshot{Templates: prompt.CompiledTemplates{Messages: []*template.Template{message}, Session: session}},
@@ -260,7 +260,7 @@ func TestRunnerInspectRequirementsReturnsIncompleteDiscoveryAsSuccess(t *testing
 		t.Fatal(err)
 	}
 	repository := &requirementInspectionPromptRepository{
-		definition:    &domain.PromptDefinition{ID: "selected", Version: "v1", DefaultProfile: "profile"},
+		definition:    &domain.PromptDefinition{ID: "selected", Version: stringPtr("v1"), DefaultProfile: "profile"},
 		snapshotFound: true,
 		snapshot:      prompt.RequirementSnapshot{Templates: prompt.CompiledTemplates{Messages: []*template.Template{compiled}}},
 	}
diff --git a/internal/usecase/resolved_targets_test.go b/internal/usecase/resolved_targets_test.go
index 43062bb..50a469d 100644
--- a/internal/usecase/resolved_targets_test.go
+++ b/internal/usecase/resolved_targets_test.go
@@ -29,7 +29,7 @@ func TestPreparationCompletesResolvedTargetThroughRequestOverrides(t *testing.T)
 		Temperature:    0, ExtraParams: map[string]any{"configured": true},
 	}, TargetPresence: domain.ExecutionTargetPresence{Temperature: true}}
 	runner := &Runner{
-		promptDefs: staticPromptRepo{def: &domain.PromptDefinition{ID: "prompt", Version: "v1", Validation: domain.OutputContract{
+		promptDefs: staticPromptRepo{def: &domain.PromptDefinition{ID: "prompt", Version: stringPtr("v1"), Validation: domain.OutputContract{
 			Format: domain.FormatText, ValidationMode: domain.ValidationNone,
 		}}},
 		profiles: staticExecutionProfileRepo{profile: profile}, renderer: staticRenderer{},
@@ -63,7 +63,7 @@ func TestResolvedTargetCredentialAvailability(t *testing.T) {
 		Endpoint: "https://provider.example/v1", Model: "model", APIKeyRequired: true,
 	}}
 	runner := &Runner{
-		promptDefs: staticPromptRepo{def: &domain.PromptDefinition{ID: "prompt", Version: "v1", Validation: domain.OutputContract{
+		promptDefs: staticPromptRepo{def: &domain.PromptDefinition{ID: "prompt", Version: stringPtr("v1"), Validation: domain.OutputContract{
 			Format: domain.FormatText, ValidationMode: domain.ValidationNone,
 		}}},
 		profiles: staticExecutionProfileRepo{profile: profile}, renderer: staticRenderer{},
diff --git a/internal/usecase/runner.go b/internal/usecase/runner.go
index 9316660..fd2bd69 100644
--- a/internal/usecase/runner.go
+++ b/internal/usecase/runner.go
@@ -252,7 +252,7 @@ func (r *Runner) executePreparedRun(
 		RawOutput:            genResp.Content,
 		Validation:           validationResult,
 		PromptID:             prepared.PromptID,
-		PromptVersion:        prepared.PromptVersion,
+		PromptVersion:        copyStringPointer(prepared.PromptVersion),
 		PromptHash:           prepared.PromptHash,
 		SessionID:            prepared.SessionID,
 		RenderedPromptHash:   prepared.RenderedPromptHash,
@@ -321,7 +321,7 @@ func (r *Runner) resolvePreparation(
 	}
 	def := promptSelection.definition
 	if recorder := observation.FromContext(ctx); recorder != nil {
-		recorder.UpdateSelection(observation.Selection{PromptID: def.ID, PromptVersion: def.Version})
+		recorder.UpdateSelection(observation.Selection{PromptID: def.ID, PromptVersion: copyStringPointer(def.Version)})
 	}
 	promptDefinitionHash := promptSelection.hash
 	effectiveContract, err := resolveOutputContract(def, req.Validation)
@@ -342,7 +342,7 @@ func (r *Runner) resolvePreparation(
 		return nil, err
 	}
 	if recorder := observation.FromContext(ctx); recorder != nil {
-		recorder.UpdateSelection(observation.Selection{PromptID: def.ID, PromptVersion: def.Version, ProfileID: selection.id})
+		recorder.UpdateSelection(observation.Selection{PromptID: def.ID, PromptVersion: copyStringPointer(def.Version), ProfileID: selection.id})
 	}
 
 	effectiveModel, targetPresence := resolveExecutionTarget(selection.profile, req.Execution)
@@ -355,7 +355,7 @@ func (r *Runner) resolvePreparation(
 		return nil, fmt.Errorf("%w: %w", ErrInvalidRequest, err)
 	}
 	if recorder := observation.FromContext(ctx); recorder != nil {
-		recorder.UpdateSelection(observation.Selection{PromptID: def.ID, PromptVersion: def.Version,
+		recorder.UpdateSelection(observation.Selection{PromptID: def.ID, PromptVersion: copyStringPointer(def.Version),
 			ProfileID: selection.id, BackendID: effectiveModel.BackendID, Model: effectiveModel.Model})
 	}
 
@@ -481,7 +481,7 @@ func (r *Runner) completePreparationWithStructuredOutput(
 	effectiveModel.APIKey = ""
 	return &domain.PreparedRun{
 		PromptID:             state.definition.ID,
-		PromptVersion:        state.definition.Version,
+		PromptVersion:        copyStringPointer(state.definition.Version),
 		PromptHash:           state.promptDefinitionHash,
 		SelectedProfileID:    state.selectedProfileID,
 		SelectedBackendID:    state.effectiveModel.BackendID,
@@ -713,3 +713,11 @@ func buildOutputArtifact(content string, format domain.OutputFormat) domain.Arti
 func hashPromptDefinition(def *domain.PromptDefinition) (string, error) {
 	return promptdef.HashDefinition(def)
 }
+
+func copyStringPointer(value *string) *string {
+	if value == nil {
+		return nil
+	}
+	copy := *value
+	return &copy
+}
diff --git a/internal/usecase/runner_test.go b/internal/usecase/runner_test.go
index 9a4fb6c..3e8cf06 100644
--- a/internal/usecase/runner_test.go
+++ b/internal/usecase/runner_test.go
@@ -366,7 +366,7 @@ func TestRunnerPrepareWithExplicitProfileSelection(t *testing.T) {
 	if err != nil {
 		t.Fatalf("expected no error, got %v", err)
 	}
-	if prepared.PromptID != "p" || prepared.PromptVersion != "1" {
+	if prepared.PromptID != "p" || prepared.PromptVersion == nil || *prepared.PromptVersion != "1" {
 		t.Fatalf("unexpected prepared prompt metadata: %+v", prepared)
 	}
 	if prepared.SelectedProfileID != "exec" {
@@ -1257,7 +1257,7 @@ func TestRunnerRunSuccessful(t *testing.T) {
 	if err != nil {
 		t.Fatalf("expected no error, got %v", err)
 	}
-	if res.PromptID != "p" || res.PromptVersion != "1" {
+	if res.PromptID != "p" || res.PromptVersion == nil || *res.PromptVersion != "1" {
 		t.Fatalf("unexpected prompt metadata: %+v", res)
 	}
 	if res.SelectedProfileID != "exec" {
@@ -2504,7 +2504,7 @@ func TestBuildOutputArtifactDefaults(t *testing.T) {
 func promptDef(format domain.OutputFormat, mode domain.ValidationMode, attempts int) *domain.PromptDefinition {
 	return &domain.PromptDefinition{
 		ID:             "p",
-		Version:        "1",
+		Version:        stringPtr("1"),
 		DefaultProfile: "exec",
 		Inputs:         []domain.PromptInput{{Name: "transcript", Required: true}},
 		Templates:      []domain.PromptMessageTemplate{{Role: "user", Content: "x"}},
diff --git a/json_contract_test.go b/json_contract_test.go
index 9ae78d4..a6d9c5b 100644
--- a/json_contract_test.go
+++ b/json_contract_test.go
@@ -12,6 +12,10 @@ import (
 	"gitea.maximumdirect.net/eric/promptkit"
 )
 
+func stringPointerForTest(value string) *string {
+	return &value
+}
+
 func TestGenerateResponseUsagePresenceJSON(t *testing.T) {
 	value := promptkit.GenerateResponse{
 		Content: "ok",
@@ -42,6 +46,45 @@ func TestGenerateResponseUsagePresenceJSON(t *testing.T) {
 	}
 }
 
+func TestPromptVersionJSONDistinguishesAbsenceAndDeclaredEmpty(t *testing.T) {
+	tests := []struct {
+		name        string
+		value       *string
+		wantPresent bool
+		wantValue   string
+	}{
+		{name: "absent"},
+		{name: "declared empty", value: stringPointerForTest(""), wantPresent: true},
+		{name: "declared text", value: stringPointerForTest("release/v1"), wantPresent: true, wantValue: "release/v1"},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			check := func(label string, marshal func() ([]byte, error)) {
+				t.Helper()
+				payload, err := marshal()
+				if err != nil {
+					t.Fatal(err)
+				}
+				object := decodeJSONObject(t, payload)
+				value, present := object["prompt_version"]
+				if present != test.wantPresent {
+					t.Errorf("%s prompt_version present=%t, want %t: %s", label, present, test.wantPresent, payload)
+				}
+				var decoded string
+				if test.wantPresent && (json.Unmarshal(value, &decoded) != nil || decoded != test.wantValue) {
+					t.Errorf("%s prompt_version=%#v, want %q", label, value, test.wantValue)
+				}
+			}
+			check("prepared", func() ([]byte, error) {
+				return json.Marshal(promptkit.PreparedRun{PromptVersion: test.value})
+			})
+			check("result", func() ([]byte, error) {
+				return json.Marshal(promptkit.RunResult{PromptVersion: test.value})
+			})
+		})
+	}
+}
+
 func TestPreparedRunJSONContractRoundTripsAllFields(t *testing.T) {
 	value := fullyPopulatedPreparedRun()
 	payload, err := json.Marshal(value)
@@ -216,7 +259,7 @@ func fullyPopulatedPreparedRun() promptkit.PreparedRun {
 	start := time.Date(2026, time.August, 11, 12, 13, 14, 150_000_000, time.UTC)
 	return promptkit.PreparedRun{
 		PromptID:             "prompt.prepared",
-		PromptVersion:        "2.1.0",
+		PromptVersion:        stringPointerForTest("2.1.0"),
 		PromptHash:           "prompt-hash",
 		SelectedProfileID:    "profile-prepared",
 		SelectedBackendID:    "backend-prepared",
@@ -283,7 +326,7 @@ func fullyPopulatedRunResult() promptkit.RunResult {
 			IsValid:        false,
 		},
 		PromptID:             "prompt.result",
-		PromptVersion:        "3.2.1",
+		PromptVersion:        stringPointerForTest("3.2.1"),
 		PromptHash:           "result-prompt-hash",
 		SessionID:            "session-result",
 		RenderedPromptHash:   "result-rendered-hash",
diff --git a/listing.go b/listing.go
index ed83faf..51581a9 100644
--- a/listing.go
+++ b/listing.go
@@ -7,10 +7,11 @@ import (
 
 // PromptIdentity identifies one prompt ID and its optional descriptive version
 // label in the effective configuration captured when an Engine is constructed.
-// It has no stable JSON representation.
+// A nil Version means no label was declared; a non-nil empty string is an
+// explicit label. It has no stable JSON representation.
 type PromptIdentity struct {
 	ID      string
-	Version string
+	Version *string
 }
 
 // ListProfiles returns profile IDs in the effective configuration captured
@@ -38,8 +39,8 @@ func (e *Engine) ListProfiles(ctx context.Context) ([]string, error) {
 
 // ListPrompts returns every prompt ID in the effective configuration captured
 // when the engine was constructed, sorted lexically by ID. Each identity may
-// include its descriptive version label. The
-// returned slice is caller-owned and safe to mutate while the engine is used
+// include its descriptive version label. The returned slice and each Version
+// pointer are caller-owned and safe to mutate while the engine is used
 // concurrently. Empty inventories succeed.
 //
 // Listing reports membership, not execution readiness. It does not reload
@@ -58,7 +59,7 @@ func (e *Engine) ListPrompts(ctx context.Context) ([]PromptIdentity, error) {
 	}
 	public := make([]PromptIdentity, len(identities))
 	for i, identity := range identities {
-		public[i] = PromptIdentity{ID: identity.ID, Version: identity.Version}
+		public[i] = PromptIdentity{ID: identity.ID, Version: copyStringPtr(identity.Version)}
 	}
 	if err := ctx.Err(); err != nil {
 		return nil, mapPublicError(err)
diff --git a/listing_contract_test.go b/listing_contract_test.go
index 4a8be7b..d38fe35 100644
--- a/listing_contract_test.go
+++ b/listing_contract_test.go
@@ -38,13 +38,13 @@ func TestListIdentitiesBasicContract(t *testing.T) {
 		t.Fatal(err)
 	}
 	want := []promptkit.PromptIdentity{
-		{ID: "example-prompt", Version: "10"},
+		{ID: "example-prompt", Version: stringPointerForTest("10")},
 	}
 	if len(prompts) != len(want) {
 		t.Fatalf("prompt listing = %#v, want %#v", prompts, want)
 	}
 	for i := range want {
-		if prompts[i] != want[i] {
+		if prompts[i].ID != want[i].ID || prompts[i].Version == nil || *prompts[i].Version != *want[i].Version {
 			t.Fatalf("prompt listing = %#v, want %#v", prompts, want)
 		}
 	}
@@ -54,7 +54,8 @@ func TestListIdentitiesBasicContract(t *testing.T) {
 		t.Fatalf("listed profile could not be inspected: (%+v, %v)", profile, err)
 	}
 	prompt, err := engine.InspectPrompt(context.Background(), prompts[0].ID)
-	if err != nil || prompt == nil || prompt.PromptID != prompts[0].ID || prompt.PromptVersion != prompts[0].Version {
+	if err != nil || prompt == nil || prompt.PromptID != prompts[0].ID || prompt.PromptVersion == nil ||
+		*prompt.PromptVersion != *prompts[0].Version {
 		t.Fatalf("listed prompt could not be inspected: (%+v, %v)", prompt, err)
 	}
 }
@@ -169,9 +170,9 @@ func TestListIdentitiesUseEffectiveLayeredMembership(t *testing.T) {
 		t.Fatal(err)
 	}
 	wantPrompts := []promptkit.PromptIdentity{
-		{ID: "main-only", Version: "v3"},
-		{ID: "shared/prompt", Version: "v2"},
-		{ID: "underlay-only", Version: "v1"},
+		{ID: "main-only", Version: stringPointerForTest("v3")},
+		{ID: "shared/prompt", Version: stringPointerForTest("v2")},
+		{ID: "underlay-only", Version: stringPointerForTest("v1")},
 	}
 	if !reflect.DeepEqual(prompts, wantPrompts) {
 		t.Fatalf("effective prompt identities = %#v, want %#v", prompts, wantPrompts)
@@ -225,7 +226,9 @@ func TestListIdentitiesAreOwnedAndSafeForConcurrentUse(t *testing.T) {
 	for i := range prompts {
 		if prompts[i].ID == "prompt" {
 			prompts[i].ID = "caller mutation"
-			prompts[i].Version = "caller mutation"
+			if prompts[i].Version != nil {
+				*prompts[i].Version = "caller mutation"
+			}
 		}
 	}
 	profiles, err = engine.ListProfiles(context.Background())
@@ -269,7 +272,9 @@ func TestListIdentitiesAreOwnedAndSafeForConcurrentUse(t *testing.T) {
 					return
 				}
 				prompts[0].ID = "worker mutation"
-				prompts[0].Version = "worker mutation"
+				if prompts[0].Version != nil {
+					*prompts[0].Version = "worker mutation"
+				}
 
 				if _, err := engine.InspectProfile(context.Background(), "profile"); err != nil {
 					results <- fmt.Errorf("inspect profile: %w", err)
@@ -345,7 +350,7 @@ func countListingProfile(profiles []string, id string) int {
 func countListingPrompt(prompts []promptkit.PromptIdentity, id, version string) int {
 	count := 0
 	for _, prompt := range prompts {
-		if prompt.ID == id && prompt.Version == version {
+		if prompt.ID == id && prompt.Version != nil && *prompt.Version == version {
 			count++
 		}
 	}
diff --git a/observation_contract_test.go b/observation_contract_test.go
index 45c9019..995b8e7 100644
--- a/observation_contract_test.go
+++ b/observation_contract_test.go
@@ -56,9 +56,17 @@ func TestRunObservationHasResolvedIdentitiesAndAccounting(t *testing.T) {
 	if len(events) != 3 || events[0].Kind != promptkit.ExecutionStarted || events[1].Kind != promptkit.ExecutionAttempt || events[2].Kind != promptkit.ExecutionFinished {
 		t.Fatalf("events=%+v", events)
 	}
-	if events[0].PromptID != "" || events[1].PromptID != "prompt" || events[1].PromptVersion != "1" || events[1].ProfileID != "profile" || events[1].Model != "model" {
+	if events[0].PromptID != "" || events[1].PromptID != "prompt" || events[1].PromptVersion == nil ||
+		*events[1].PromptVersion != "1" || events[1].ProfileID != "profile" || events[1].Model != "model" {
 		t.Fatalf("selection=%+v", events)
 	}
+	if events[1].PromptVersion == events[2].PromptVersion {
+		t.Fatal("execution events share a mutable version label")
+	}
+	*events[1].PromptVersion = "mutated event"
+	if events[2].PromptVersion == nil || *events[2].PromptVersion != "1" {
+		t.Fatal("mutating one event changed another event's version label")
+	}
 	if result.RunID == "" || events[0].RunID != result.RunID || events[2].RunID != result.RunID || events[2].Attempts != 1 || events[2].TransientRetries != 0 || events[2].RepairCalls != 0 || events[2].Outcome != promptkit.ExecutionOutcomeSuccess {
 		t.Fatalf("result=%+v terminal=%+v", result, events[2])
 	}
diff --git a/observations.go b/observations.go
index 6d16b70..f610560 100644
--- a/observations.go
+++ b/observations.go
@@ -100,11 +100,13 @@ type ObservedTokenUsage struct {
 // its output. Failure is classified metadata; RetriesExhausted is a separate
 // flag and does not replace the underlying failure kind.
 type ExecutionEvent struct {
-	Kind               ExecutionEventKind
-	RunID              string
-	Time               time.Time
-	PromptID           string
-	PromptVersion      string
+	Kind     ExecutionEventKind
+	RunID    string
+	Time     time.Time
+	PromptID string
+	// PromptVersion is the selected definition's descriptive label. Each event
+	// owns its pointer; nil means absent while a non-nil empty string is explicit.
+	PromptVersion      *string
 	ProfileID          string
 	BackendID          string
 	Model              string
@@ -131,7 +133,7 @@ func fromDomainExecutionEvent(value domain.ExecutionEvent) ExecutionEvent {
 	}
 	return ExecutionEvent{
 		Kind: ExecutionEventKind(value.Kind), RunID: value.RunID, Time: value.Time,
-		PromptID: value.PromptID, PromptVersion: value.PromptVersion, ProfileID: value.ProfileID,
+		PromptID: value.PromptID, PromptVersion: copyStringPtr(value.PromptVersion), ProfileID: value.ProfileID,
 		BackendID: value.BackendID, Model: value.Model, Generation: value.Generation,
 		Attempt: value.Attempt, Dispatched: value.Dispatched, CapacityWait: value.CapacityWait,
 		GenerationDuration: value.GenerationDuration, RetryDelay: value.RetryDelay, Duration: value.Duration,
diff --git a/prepared_execution_contract_test.go b/prepared_execution_contract_test.go
index 52d0104..e378d92 100644
--- a/prepared_execution_contract_test.go
+++ b/prepared_execution_contract_test.go
@@ -87,13 +87,18 @@ func TestPreparedExecutionFreezesSourcesAndReturnsIndependentDetails(t *testing.
 	reader.set("changed artifact", "changed-input-hash")
 
 	first := prepared.Details()
+	if first.PromptVersion == nil || *first.PromptVersion != "1" {
+		t.Fatalf("prepared label = %v, want 1", *first.PromptVersion)
+	}
+	*first.PromptVersion = "mutated details"
 	first.Messages[0].Content = "changed details"
 	first.InputHashes["input"] = "changed-details-hash"
 	first.EffectiveModelParams.ExtraParams["nested"].(map[string]any)["source"] = "changed details"
 	first.StructuredOutput.JSONSchema.Schema.(map[string]any)["title"] = "changed details"
 
 	second := prepared.Details()
-	if second.Messages[0].Content != "Input=original artifact Label=original variable" {
+	if second.PromptVersion == nil || *second.PromptVersion != "1" ||
+		second.Messages[0].Content != "Input=original artifact Label=original variable" {
 		t.Fatalf("details message changed: %q", second.Messages[0].Content)
 	}
 	if second.InputHashes["input"] != "original-input-hash" {
@@ -132,7 +137,7 @@ func TestPreparedExecutionFreezesSourcesAndReturnsIndependentDetails(t *testing.
 		t.Fatalf("generation did not use frozen details:\nrequest=%+v\ndetails=%+v", generated, second)
 	}
 	if result.PromptID != second.PromptID ||
-		result.PromptVersion != second.PromptVersion ||
+		result.PromptVersion == nil || second.PromptVersion == nil || *result.PromptVersion != *second.PromptVersion ||
 		result.PromptHash != second.PromptHash ||
 		result.SessionID != second.SessionID ||
 		result.RenderedPromptHash != second.RenderedPromptHash ||
@@ -142,6 +147,13 @@ func TestPreparedExecutionFreezesSourcesAndReturnsIndependentDetails(t *testing.
 		!reflect.DeepEqual(result.InputHashes, second.InputHashes) {
 		t.Fatalf("result provenance does not match details:\nresult=%+v\ndetails=%+v", result, second)
 	}
+	if result.PromptVersion == second.PromptVersion {
+		t.Fatal("run result and prepared details share a mutable version label")
+	}
+	*result.PromptVersion = "mutated result"
+	if *second.PromptVersion != "1" {
+		t.Fatal("run result label mutation reached prepared details")
+	}
 }
 
 func TestPreparedExecutionLifecycleAndEngineBinding(t *testing.T) {
diff --git a/requirements.go b/requirements.go
index f27e9d5..fb906fc 100644
--- a/requirements.go
+++ b/requirements.go
@@ -116,7 +116,8 @@ type RequirementIssue struct {
 // prompt context. Input and variable entries are sorted by exact name. Issues
 // are deduplicated by code and associated names, then sorted by that tuple.
 // Their descriptions and entry explanations are safe summaries, not
-// machine-readable details.
+// machine-readable details. PromptVersion is caller-owned: nil means no label
+// was declared; a non-nil empty string is explicit.
 //
 // Complete describes the supported analysis's discovery coverage, not whether
 // requirements are supplied, templates will render, artifacts or schemas are
@@ -128,8 +129,9 @@ type RequirementIssue struct {
 type RequirementInspection struct {
 	// PromptID is the selected exact prompt ID.
 	PromptID string
-	// PromptVersion is the selected definition's descriptive version label.
-	PromptVersion string
+	// PromptVersion is the selected definition's descriptive version label. Nil
+	// means no label was declared; a non-nil empty string is an explicit label.
+	PromptVersion *string
 	// ProfileID is the selected profile identity; it does not indicate
 	// execution readiness.
 	ProfileID string
@@ -200,7 +202,7 @@ func fromDomainRequirementInspection(inspection *domain.RequirementInspection) *
 		return nil
 	}
 	result := &RequirementInspection{
-		PromptID: inspection.PromptID, PromptVersion: inspection.PromptVersion,
+		PromptID: inspection.PromptID, PromptVersion: copyRequirementString(inspection.PromptVersion),
 		ProfileID: inspection.ProfileID, Complete: inspection.Complete,
 		Inputs:    make([]InputRequirement, len(inspection.Inputs)),
 		Variables: make([]VariableRequirement, len(inspection.Variables)),
diff --git a/requirements_inspection_benchmark_test.go b/requirements_inspection_benchmark_test.go
index 9f653d3..5d2a567 100644
--- a/requirements_inspection_benchmark_test.go
+++ b/requirements_inspection_benchmark_test.go
@@ -51,7 +51,7 @@ func BenchmarkRequirementInspection(b *testing.B) {
 			PromptID: "inspection", ProfileID: profileID, Vars: map[string]string{"name": "Ada"},
 		}
 		inspection, err := engine.InspectRequirements(ctx, request)
-		if err != nil || inspection.PromptID != "inspection" || inspection.PromptVersion != "1" ||
+		if err != nil || inspection.PromptID != "inspection" || inspection.PromptVersion == nil || *inspection.PromptVersion != "1" ||
 			inspection.ProfileID != profileID || !inspection.Complete || len(inspection.Inputs) != 1 ||
 			inspection.Inputs[0].Name != "transcript" || inspection.Inputs[0].Kind != promptkit.RequirementRequired ||
 			len(inspection.Variables) != 1 || inspection.Variables[0].Name != "name" || !inspection.Variables[0].Supplied {
diff --git a/requirements_inspection_contract_test.go b/requirements_inspection_contract_test.go
index 79f287e..fe6e06f 100644
--- a/requirements_inspection_contract_test.go
+++ b/requirements_inspection_contract_test.go
@@ -85,7 +85,7 @@ func TestInspectRequirementsEnumeratesCapturedDependenciesAndInactiveNames(t *te
 	if err != nil {
 		t.Fatalf("inspect before artifacts, credentials, and schemas exist: %v", err)
 	}
-	if inspection.PromptID != "requirements" || inspection.PromptVersion != "v1" || inspection.ProfileID != "partial" || !inspection.Complete {
+	if inspection.PromptID != "requirements" || inspection.PromptVersion == nil || *inspection.PromptVersion != "v1" || inspection.ProfileID != "partial" || !inspection.Complete {
 		t.Fatalf("selected context or completeness is wrong: %+v", inspection)
 	}
 	inputs := make(map[string]promptkit.InputRequirement, len(inspection.Inputs))
@@ -146,13 +146,13 @@ func TestInspectRequirementsUsesPromptIDsAndProfileIdentity(t *testing.T) {
 	}
 	engine := requirementsEngine(t, prompts, profiles)
 	first, err := engine.InspectRequirements(context.Background(), promptkit.RequirementInspectionRequest{PromptID: "first-prompt"})
-	if err != nil || first.PromptVersion != "v1" || first.ProfileID != "first" || len(first.Inputs) != 1 || first.Inputs[0].Name != "one" {
+	if err != nil || first.PromptVersion == nil || *first.PromptVersion != "v1" || first.ProfileID != "first" || len(first.Inputs) != 1 || first.Inputs[0].Name != "one" {
 		t.Fatalf("first prompt ID/default profile=(%+v, %v)", first, err)
 	}
 	second, err := engine.InspectRequirements(context.Background(), promptkit.RequirementInspectionRequest{
 		PromptID: "second-prompt", ProfileID: "first",
 	})
-	if err != nil || second.PromptVersion != "v2" || second.ProfileID != "first" || second.Inputs[0].Name != "two" {
+	if err != nil || second.PromptVersion == nil || *second.PromptVersion != "v2" || second.ProfileID != "first" || second.Inputs[0].Name != "two" {
 		t.Fatalf("second prompt ID/request profile=(%+v, %v)", second, err)
 	}
 	if _, err := engine.InspectRequirements(context.Background(), promptkit.RequirementInspectionRequest{PromptID: "First-Prompt"}); !errors.Is(err, promptkit.ErrPromptNotFound) {
@@ -288,6 +288,10 @@ func TestInspectRequirementsReturnsIndependentValuesAndCanOverlapPreparation(t *
 	if err != nil {
 		t.Fatal(err)
 	}
+	if first.PromptVersion == nil || *first.PromptVersion != "v1" {
+		t.Fatalf("requirement inspection label = %v, want v1", first.PromptVersion)
+	}
+	*first.PromptVersion = "mutated label"
 	for index := range first.Inputs {
 		if first.Inputs[index].Name == "declared" {
 			first.Inputs[index].Name = "mutated"
@@ -308,7 +312,8 @@ func TestInspectRequirementsReturnsIndependentValuesAndCanOverlapPreparation(t *
 			description = input.Description
 		}
 	}
-	if second.Inputs[0].Name == "mutated" || second.Variables[0].Name != "decision" ||
+	if second.PromptVersion == nil || *second.PromptVersion != "v1" ||
+		second.Inputs[0].Name == "mutated" || second.Variables[0].Name != "decision" ||
 		description == nil || *description != "captured description" ||
 		len(second.Issues) != 1 || second.Issues[0].Description == "mutated issue" {
 		t.Fatalf("result mutation reached captured state or later result: (%+v, %v)", second, err)
diff --git a/smoke_diagnostics.go b/smoke_diagnostics.go
index 770ff81..1fbb213 100644
--- a/smoke_diagnostics.go
+++ b/smoke_diagnostics.go
@@ -116,9 +116,10 @@ type SmokeTestTarget struct {
 	// ProfileID is the selected profile, if any.
 	ProfileID string
 	// PromptID identifies the selected prompt; PromptVersion carries its
-	// descriptive version label, if any.
+	// descriptive version label. Nil means absent while a non-nil empty string is
+	// explicit. The pointer belongs to this returned target.
 	PromptID      string
-	PromptVersion string
+	PromptVersion *string
 	// DefaultSourceBackendID identifies the backend whose configured default
 	// selected the profile, when that selection path was used.
 	DefaultSourceBackendID string
@@ -305,7 +306,7 @@ func fromDomainSmokeTestReport(report domain.SmokeTestReport) (*SmokeTestReport,
 			BackendID:              report.Target.BackendID,
 			ProfileID:              report.Target.ProfileID,
 			PromptID:               report.Target.PromptID,
-			PromptVersion:          report.Target.PromptVersion,
+			PromptVersion:          copyStringPtr(report.Target.PromptVersion),
 			DefaultSourceBackendID: report.Target.DefaultSourceBackendID,
 			SelectionSource:        report.Target.SelectionSource,
 			Endpoint:               report.Target.Endpoint,
diff --git a/smoke_integration_contract_test.go b/smoke_integration_contract_test.go
index 061e03b..ff63527 100644
--- a/smoke_integration_contract_test.go
+++ b/smoke_integration_contract_test.go
@@ -291,6 +291,9 @@ func TestSmokeTestUsesPrivateInferenceWithoutApplicationResourcesOrListingChange
 	if err != nil || report == nil || !report.Completed {
 		t.Fatalf("structured smoke test=(%+v, %v)", report, err)
 	}
+	if report.Target.PromptVersion == nil || *report.Target.PromptVersion != "1" {
+		t.Fatalf("smoke target label = %v, want 1", report.Target.PromptVersion)
+	}
 	if reader.calls != 0 || schemaSource.openCount() != schemaOpensBefore {
 		t.Fatalf("application resources used: artifact reads=%d schema opens before=%d after=%d", reader.calls, schemaOpensBefore, schemaSource.openCount())
 	}
@@ -322,6 +325,15 @@ func TestSmokeTestUsesPrivateInferenceWithoutApplicationResourcesOrListingChange
 			t.Errorf("smoke report exposed %q", private)
 		}
 	}
+	firstLabel := report.Target.PromptVersion
+	*firstLabel = "mutated report"
+	secondReport, err := engine.SmokeTest(context.Background(), promptkit.SmokeTestRequest{
+		Kind: promptkit.SmokeTestStructuredOutput, PromptID: "application-prompt", APIKey: "synthetic-smoke-key-marker",
+	})
+	if err != nil || secondReport == nil || !secondReport.Completed || secondReport.Target.PromptVersion == nil ||
+		*secondReport.Target.PromptVersion != "1" || secondReport.Target.PromptVersion == firstLabel {
+		t.Fatalf("smoke target label was not independently owned: (%+v, %v)", secondReport, err)
+	}
 	profilesAfter, err := engine.ListProfiles(context.Background())
 	if err != nil {
 		t.Fatal(err)
diff --git a/types.go b/types.go
index 07ca25e..b968ee1 100644
--- a/types.go
+++ b/types.go
@@ -159,8 +159,10 @@ type RunRequest struct {
 type PreparedRun struct {
 	// PromptID is the selected prompt identifier.
 	PromptID string `json:"prompt_id"`
-	// PromptVersion is the selected definition's descriptive version label.
-	PromptVersion string `json:"prompt_version,omitempty"`
+	// PromptVersion is the selected definition's descriptive version label. Nil
+	// means no label was declared; a non-nil empty string is explicit. JSON omits
+	// nil and preserves a declared empty string.
+	PromptVersion *string `json:"prompt_version,omitempty"`
 	// PromptHash is an opaque equality value for the selected definition.
 	PromptHash string `json:"prompt_hash,omitempty"`
 	// SelectedProfileID is the explicit request profile or prompt default that
@@ -217,8 +219,10 @@ type RunResult struct {
 	Validation ValidationResult `json:"validation"`
 	// PromptID is the selected prompt identifier.
 	PromptID string `json:"prompt_id"`
-	// PromptVersion is the selected definition's descriptive version label.
-	PromptVersion string `json:"prompt_version,omitempty"`
+	// PromptVersion is the selected definition's descriptive version label. Nil
+	// means no label was declared; a non-nil empty string is explicit. JSON omits
+	// nil and preserves a declared empty string.
+	PromptVersion *string `json:"prompt_version,omitempty"`
 	// PromptHash is the same opaque definition equality value exposed by
 	// PreparedRun.
 	PromptHash string `json:"prompt_hash,omitempty"`
@@ -394,14 +398,17 @@ type PromptInputDefinition struct {
 // PromptInspection is the caller-owned result of [Engine.InspectPrompt].
 // It has no stable JSON representation.
 //
-// Inputs contains copied declared input metadata in definition order.
+// PromptVersion is caller-owned metadata: nil means no label was declared and
+// a non-nil empty string is explicit. Inputs contains copied declared input
+// metadata in definition order.
 // OutputContract is the normalized contract declared by the prompt definition,
 // rather than a request-level effective override. PromptHash is opaque.
 type PromptInspection struct {
 	// PromptID is the normalized ID of the selected prompt definition.
 	PromptID string
-	// PromptVersion is the selected definition's descriptive version label.
-	PromptVersion string
+	// PromptVersion is the selected definition's descriptive version label. Nil
+	// means no label was declared; a non-nil empty string is an explicit label.
+	PromptVersion *string
 	// PromptHash is the opaque equality value for the selected definition.
 	PromptHash string
 	// DefaultProfileID is declared metadata and is not resolved by inspection.