diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 81d0183..4600927 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -410,6 +410,17 @@ configured-default/runtime-override diagnostics through the public facade.
 
 ## Stage 15: Verify Cross-Path Ownership And Runtime Compatibility
 
+**Completed:** Cross-path checks cover mutations by an injected client on both
+initial and repair requests, detached results and details, concurrent details
+with claim/discard, and typed, numeric, null, cyclic, unsupported, and deep
+runtime provider values. Remaining validating copies serve configuration
+acceptance/overlay or public override acceptance; outward projections and schema
+detachment remain ownership boundaries. Go 1.27.3 `go test -race
+./internal/usecase ./internal/configuration ./internal/jsonvalue . -run
+'Prepared|Provider|Extra|Smoke|Profile|Schema'` passed (the filtered jsonvalue
+package selected no tests); the full `go test -race ./internal/jsonvalue` passed
+separately.
+
 **Findings:** 5–8. **Scope:** focused existing public and package contract tests.
 
 1. Reconcile the ownership inventory with the delivered call paths. Verify that
diff --git a/prepared_execution_contract_test.go b/prepared_execution_contract_test.go
index 70ff4cd..3de1299 100644
--- a/prepared_execution_contract_test.go
+++ b/prepared_execution_contract_test.go
@@ -307,6 +307,95 @@ func TestPreparedExecutionRepairsEmptyBasicOutput(t *testing.T) {
 	}
 }
 
+func TestPreparedExecutionIsolatesMutatingClientAcrossRepair(t *testing.T) {
+	client := &mutatingRepairClient{}
+	engine, err := promptkit.NewEngine(preparedContractConfig("original message", false),
+		promptkit.WithSchemaFS(preparedSchemaSource(), "."), promptkit.WithLLMClient(client))
+	if err != nil {
+		t.Fatal(err)
+	}
+	prepared, err := engine.PrepareExecution(context.Background(), promptkit.RunRequest{
+		PromptID: "prepared",
+		Execution: &promptkit.ExecutionTargetOverride{ExtraParams: map[string]any{
+			"nested": map[string]any{"value": "original"},
+		}},
+		Validation:       &promptkit.OutputContract{Format: promptkit.FormatJSON, ValidationMode: promptkit.ValidationJSONSchema, SchemaPath: "schema.json", RepairAttempts: 1},
+		AppendedMessages: []promptkit.RenderedMessage{{Role: "user", Content: "appended", CacheControl: &promptkit.CacheControl{Type: promptkit.CacheControlEphemeral, TTL: "1h"}}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	before := prepared.Details()
+	result, err := engine.RunPrepared(context.Background(), prepared)
+	if err != nil || result == nil || result.Validation.Status != promptkit.ValidationPassed || client.calls != 2 {
+		t.Fatalf("run result = %+v, error = %v, calls = %d", result, err, client.calls)
+	}
+	if !reflect.DeepEqual(before, prepared.Details()) {
+		t.Fatal("client mutation changed retained prepared metadata")
+	}
+	result.EffectiveModelParams.ExtraParams["nested"].(map[string]any)["value"] = "result mutation"
+	if prepared.Details().EffectiveModelParams.ExtraParams["nested"].(map[string]any)["value"] != "original" {
+		t.Fatal("result mutation changed retained prepared metadata")
+	}
+}
+
+type mutatingRepairClient struct{ calls int }
+
+func (c *mutatingRepairClient) Generate(_ context.Context, request promptkit.GenerateRequest) (*promptkit.GenerateResponse, error) {
+	c.calls++
+	if len(request.Prompt.Messages) < 2 || request.Prompt.Messages[0].Content != "original message" ||
+		request.Prompt.Messages[1].Content != "appended" || request.Prompt.Messages[1].CacheControl == nil ||
+		request.Prompt.Messages[1].CacheControl.TTL != "1h" ||
+		request.Target.ExtraParams["nested"].(map[string]any)["value"] != "original" ||
+		request.StructuredOutput.JSONSchema.Schema.(map[string]any)["title"] != "original root" {
+		return nil, fmt.Errorf("generation %d received mutated request", c.calls)
+	}
+	request.Prompt.Messages[0].Content = "client mutation"
+	request.Prompt.Messages[1].CacheControl.TTL = "client mutation"
+	request.Target.ExtraParams["nested"].(map[string]any)["value"] = "client mutation"
+	request.StructuredOutput.JSONSchema.Schema.(map[string]any)["title"] = "client mutation"
+	if c.calls == 1 {
+		return &promptkit.GenerateResponse{Content: `{"value":"invalid"}`}, nil
+	}
+	return &promptkit.GenerateResponse{Content: `{"value":3}`}, nil
+}
+
+type runtimeLabels []string
+type runtimeCounts map[string]int
+
+func TestPreparedExecutionRuntimeProviderValues(t *testing.T) {
+	engine := newPreparedContractEngine(t, &preparedRecordingClient{response: &promptkit.GenerateResponse{Content: "ok"}}, "message")
+	labels := runtimeLabels{"original"}
+	counts := runtimeCounts{"count": 3}
+	request := promptkit.RunRequest{PromptID: "prepared", Execution: &promptkit.ExecutionTargetOverride{ExtraParams: map[string]any{
+		"labels": labels, "counts": counts, "number": json.Number("9007199254740993"), "null": nil,
+	}}}
+	prepared, err := engine.PrepareExecution(context.Background(), request)
+	if err != nil {
+		t.Fatal(err)
+	}
+	labels[0], counts["count"] = "changed", 9
+	details := prepared.Details().EffectiveModelParams.ExtraParams
+	if details["labels"].(runtimeLabels)[0] != "original" || details["counts"].(runtimeCounts)["count"] != 3 ||
+		details["number"] != json.Number("9007199254740993") || details["null"] != nil {
+		t.Fatalf("runtime values changed: %#v", details)
+	}
+	cycle := map[string]any{}
+	cycle["self"] = cycle
+	var deep any = "leaf"
+	for range 150 {
+		deep = map[string]any{"child": deep}
+	}
+	for name, invalid := range map[string]any{"cyclic": cycle, "unsupported": func() {}, "too deep": deep} {
+		t.Run(name, func(t *testing.T) {
+			_, err := engine.PrepareExecution(context.Background(), promptkit.RunRequest{PromptID: "prepared", Execution: &promptkit.ExecutionTargetOverride{ExtraParams: map[string]any{"value": invalid}}})
+			if !errors.Is(err, promptkit.ErrInvalidRequest) {
+				t.Fatalf("invalid runtime provider value error = %v", err)
+			}
+		})
+	}
+}
+
 func TestPreparedExecutionConcurrentClaimAllowsOneGeneration(t *testing.T) {
 	release := make(chan struct{})
 	client := &preparedRecordingClient{
@@ -383,6 +472,7 @@ func TestPreparedExecutionRunAndDiscardRaceHasOneWinner(t *testing.T) {
 		}
 		runOutcome := make(chan outcome, 1)
 		discardDone := make(chan struct{})
+		detailsDone := make(chan bool, 1)
 
 		go func() {
 			<-start
@@ -394,10 +484,23 @@ func TestPreparedExecutionRunAndDiscardRaceHasOneWinner(t *testing.T) {
 			prepared.Discard()
 			close(discardDone)
 		}()
+		go func() {
+			<-start
+			for range 20 {
+				if prepared.Details().PromptID != "prepared" {
+					detailsDone <- false
+					return
+				}
+			}
+			detailsDone <- true
+		}()
 
 		close(start)
 		runResult := <-runOutcome
 		<-discardDone
+		if !<-detailsDone {
+			t.Fatalf("attempt %d lost details during lifecycle race", i)
+		}
 		calls := len(client.snapshot())
 		switch {
 		case runResult.err == nil: