Compose appended request messages

appended_messages_contract_test.go

@@ -3,6 +3,7 @@ package promptkit_test
 import (
 	"context"
 	"errors"
+	"reflect"
 	"sync/atomic"
 	"testing"
 
@@ -21,6 +22,85 @@ func TestAppendedMessageRoleConstantsAreStrings(t *testing.T) {
 	}
 }
 
+func TestAppendedMessagesComposeFrozenEffectivePrompt(t *testing.T) {
+	cacheControl := &promptkit.CacheControl{Type: promptkit.CacheControlEphemeral, TTL: "1h"}
+	appended := []promptkit.RenderedMessage{
+		{Role: " \tAsSiStAnT\n", Content: "previous response"},
+		{Role: promptkit.RoleUser, Content: "corrective request", CacheControl: cacheControl},
+	}
+	client := &fakeLLMClient{response: &promptkit.GenerateResponse{Content: "output"}}
+	engine, err := promptkit.NewEngine(
+		promptkit.Config{},
+		promptkit.WithPromptFS(contractPromptFS("prompt", "profile", "configured prompt"), "."),
+		promptkit.WithProfiles(promptkit.Profile{ID: "profile", Endpoint: "http://example.test/v1", Model: "model"}),
+		promptkit.WithLLMClient(client),
+	)
+	if err != nil {
+		t.Fatalf("construct engine: %v", err)
+	}
+	request := promptkit.RunRequest{PromptID: "prompt", AppendedMessages: appended}
+
+	plain, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+	if err != nil {
+		t.Fatalf("prepare plain request: %v", err)
+	}
+	prepared, err := engine.Prepare(context.Background(), request)
+	if err != nil {
+		t.Fatalf("prepare appended request: %v", err)
+	}
+	expected := []promptkit.RenderedMessage{
+		{Role: promptkit.RoleUser, Content: "configured prompt"},
+		{Role: promptkit.RoleAssistant, Content: "previous response"},
+		{Role: promptkit.RoleUser, Content: "corrective request", CacheControl: &promptkit.CacheControl{Type: promptkit.CacheControlEphemeral, TTL: "1h"}},
+	}
+	if !reflect.DeepEqual(prepared.Messages, expected) || prepared.PromptHash != plain.PromptHash || prepared.RenderedPromptHash == plain.RenderedPromptHash {
+		t.Fatalf("prepared effective prompt = %#v, plain = %#v", prepared, plain)
+	}
+
+	equivalent, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt", AppendedMessages: []promptkit.RenderedMessage{
+		{Role: promptkit.RoleAssistant, Content: "previous response"},
+		{Role: promptkit.RoleUser, Content: "corrective request", CacheControl: &promptkit.CacheControl{Type: promptkit.CacheControlEphemeral, TTL: "1h"}},
+	}})
+	if err != nil || equivalent.RenderedPromptHash != prepared.RenderedPromptHash {
+		t.Fatalf("normalized-equivalent request = (%#v, %v), want matching rendered hash %q", equivalent, err, prepared.RenderedPromptHash)
+	}
+
+	for _, variant := range []promptkit.RunRequest{
+		{PromptID: "prompt", AppendedMessages: []promptkit.RenderedMessage{{Role: promptkit.RoleAssistant, Content: "changed"}, expected[2]}},
+		{PromptID: "prompt", AppendedMessages: []promptkit.RenderedMessage{expected[2], expected[1]}},
+		{PromptID: "prompt", AppendedMessages: []promptkit.RenderedMessage{{Role: promptkit.RoleAssistant, Content: "previous response"}, {Role: promptkit.RoleUser, Content: "corrective request"}}},
+	} {
+		variantPrepared, prepareErr := engine.Prepare(context.Background(), variant)
+		if prepareErr != nil || variantPrepared.RenderedPromptHash == prepared.RenderedPromptHash || variantPrepared.PromptHash != prepared.PromptHash {
+			t.Fatalf("variant preparation = (%#v, %v)", variantPrepared, prepareErr)
+		}
+	}
+
+	result, err := engine.Run(context.Background(), request)
+	if err != nil || result.RenderedPromptHash != prepared.RenderedPromptHash || !reflect.DeepEqual(client.requests[0].Prompt.Messages, expected) {
+		t.Fatalf("run result = (%#v, %v), request = %#v", result, err, client.requests)
+	}
+
+	execution, err := engine.PrepareExecution(context.Background(), request)
+	if err != nil {
+		t.Fatalf("prepare execution: %v", err)
+	}
+	appended[0].Content = "changed caller content"
+	cacheControl.TTL = ""
+	firstDetails := execution.Details()
+	firstDetails.Messages[1].Content = "changed details content"
+	firstDetails.Messages[2].CacheControl.Type = "changed details cache"
+	secondDetails := execution.Details()
+	if !reflect.DeepEqual(secondDetails.Messages, expected) || secondDetails.RenderedPromptHash != prepared.RenderedPromptHash {
+		t.Fatalf("prepared execution details = %#v, want frozen %#v", secondDetails, expected)
+	}
+
+	result, err = engine.RunPrepared(context.Background(), execution)
+	if err != nil || result.RenderedPromptHash != prepared.RenderedPromptHash || !reflect.DeepEqual(client.requests[1].Prompt.Messages, expected) {
+		t.Fatalf("prepared result = (%#v, %v), requests = %#v", result, err, client.requests)
+	}
+}
+
 func TestInvalidAppendedMessagesFailBeforeSourceOrModelWork(t *testing.T) {
 	promptSource := &inspectionCountingFS{}
 	var modelCalls atomic.Int64

docs/roadmap/implementation.md

@@ -238,6 +238,8 @@ The runner may still ignore the new domain field until Stage 3.
 
 ## Stage 3: Compose, Freeze, Hash, Execute, And Repair The Effective Prompt
 
+**Status:** Complete
+
 ### Objective
 
 Make appended messages part of the effective rendered prompt everywhere after

generation_error_contract_test.go

@@ -39,6 +39,23 @@ func TestBuiltInGenerationError(t *testing.T) {
 	assertGenerationError(t, err, http.StatusServiceUnavailable, "", "", "")
 }
 
+func TestBuiltInGenerationErrorWithAppendedMessages(t *testing.T) {
+	const messageMarker = "combined-request-provider-marker"
+	engine := newBuiltInGenerationErrorEngine(t, http.StatusUnprocessableEntity,
+		`{"error":{"message":"`+messageMarker+`"}}`)
+	request := generationErrorRunRequest()
+	request.AppendedMessages = []promptkit.RenderedMessage{
+		{Role: promptkit.RoleAssistant, Content: "previous response"},
+		{Role: promptkit.RoleUser, Content: "consumer correction"},
+	}
+
+	result, err := engine.Run(context.Background(), request)
+	if result != nil {
+		t.Fatalf("Run result = %#v, want nil", result)
+	}
+	assertGenerationError(t, err, http.StatusUnprocessableEntity, "", "", messageMarker)
+}
+
 func TestBuiltInRepairGenerationError(t *testing.T) {
 	const (
 		codeMarker    = "repair-code-marker"

internal/domain/message.go

@@ -59,20 +59,24 @@ func NormalizeCacheControl(control *CacheControl) (*CacheControl, error) {
 // CloneRenderedMessages returns a deep copy of rendered messages.
 func CloneRenderedMessages(messages []RenderedMessage) []RenderedMessage {
 	cloned := make([]RenderedMessage, len(messages))
-	for index, message := range messages {
+	copyRenderedMessages(cloned, messages)
-		cloned[index] = message
-		if message.CacheControl != nil {
-			cacheControl := *message.CacheControl
-			cloned[index].CacheControl = &cacheControl
-		}
-	}
 	return cloned
 }
 
 // ConcatRenderedMessages returns an independently owned concatenation of messages.
 func ConcatRenderedMessages(prefix, suffix []RenderedMessage) []RenderedMessage {
-	messages := make([]RenderedMessage, 0, len(prefix)+len(suffix))
+	messages := make([]RenderedMessage, len(prefix)+len(suffix))
-	messages = append(messages, CloneRenderedMessages(prefix)...)
+	copyRenderedMessages(messages, prefix)
-	messages = append(messages, CloneRenderedMessages(suffix)...)
+	copyRenderedMessages(messages[len(prefix):], suffix)
 	return messages
 }
+
+func copyRenderedMessages(destination, source []RenderedMessage) {
+	for index, message := range source {
+		destination[index] = message
+		if message.CacheControl != nil {
+			cacheControl := *message.CacheControl
+			destination[index].CacheControl = &cacheControl
+		}
+	}
+}

internal/llm/openai_compatible_client_test.go

@@ -363,6 +363,7 @@ func TestOpenAICompatibleClientRequestMapping(t *testing.T) {
 		run  func(*testing.T)
 	}{
 		{name: "complete request and response mapping", run: checkCompleteRequestAndResponseMapping},
+		{name: "canonical role and exact content", run: checkCanonicalRoleAndExactContentMapping},
 		{name: "cache-controlled message", run: checkCacheControlledMessageMapping},
 		{name: "empty cache-control TTL", run: checkEmptyCacheControlTTLOmission},
 		{name: "session ID", run: checkSessionIDMapping},
@@ -377,6 +378,34 @@ func TestOpenAICompatibleClientRequestMapping(t *testing.T) {
 	}
 }
 
+func checkCanonicalRoleAndExactContentMapping(t *testing.T) {
+	provider := newRecordingProvider(t)
+	client := newProviderClient(t, provider, OpenAICompatibleConfig{})
+	const content = "  exact content\nwith whitespace  "
+	_, err := client.Generate(context.Background(), domain.GenerateRequest{
+		Prompt: domain.RenderedPrompt{Messages: []domain.RenderedMessage{{
+			Role:    domain.RoleDeveloper,
+			Content: content,
+		}}},
+		Target: domain.ExecutionTarget{Model: "model"},
+	})
+	if err != nil {
+		t.Fatalf("Generate() error = %v", err)
+	}
+
+	var messages []struct {
+		Role    string `json:"role"`
+		Content string `json:"content"`
+	}
+	request := provider.lastRequest(t)
+	if !request.decodeField(t, "messages", &messages) || len(messages) != 1 {
+		t.Fatalf("messages = %#v, want one message", messages)
+	}
+	if messages[0].Role != domain.RoleDeveloper || messages[0].Content != content {
+		t.Fatalf("message = %#v, want role %q and exact content %q", messages[0], domain.RoleDeveloper, content)
+	}
+}
+
 func checkCompleteRequestAndResponseMapping(t *testing.T) {
 	provider := newRecordingProvider(t)
 	provider.respond(http.StatusOK, `{

internal/usecase/prepared_execution.go

@@ -213,16 +213,7 @@ func clonePreparedRun(source *domain.PreparedRun) (*domain.PreparedRun, error) {
 			copied.InputHashes[name] = hash
 		}
 	}
-	if source.Messages != nil {
+	copied.Messages = domain.CloneRenderedMessages(source.Messages)
-		copied.Messages = make([]domain.RenderedMessage, len(source.Messages))
-		for i, message := range source.Messages {
-			copied.Messages[i] = message
-			if message.CacheControl != nil {
-				cacheControl := *message.CacheControl
-				copied.Messages[i].CacheControl = &cacheControl
-			}
-		}
-	}
 
 	if source.StructuredOutput != nil {
 		structuredOutput := *source.StructuredOutput

internal/usecase/repairer.go

@@ -55,8 +55,7 @@ func (r *defaultOutputRepairer) Repair(ctx context.Context, req RepairRequest) (
 		return nil, err
 	}
 
-	messages := make([]domain.RenderedMessage, len(req.OriginalMessages), len(req.OriginalMessages)+2)
+	messages := domain.ConcatRenderedMessages(req.OriginalMessages, nil)
-	copy(messages, req.OriginalMessages)
 	if strings.TrimSpace(req.PreviousOutput) != "" {
 		messages = append(messages, domain.RenderedMessage{
 			Role:    domain.RoleAssistant,

internal/usecase/repairer_test.go

@@ -30,6 +30,8 @@ func TestDefaultOutputRepairerBuildsFullContextRequest(t *testing.T) {
 	original := []domain.RenderedMessage{
 		{Role: "system", Content: "Follow the task.", CacheControl: &domain.CacheControl{Type: domain.CacheControlEphemeral, TTL: "1h"}},
 		{Role: "user", Content: "Summarize the report."},
+		{Role: "assistant", Content: "Consumer-supplied previous response."},
+		{Role: "user", Content: "Consumer-supplied correction."},
 	}
 	before := append([]domain.RenderedMessage(nil), original...)
 	previous := strings.Repeat("candidate ", 12_000)

internal/usecase/runner.go

@@ -4,10 +4,13 @@ import (
 	"context"
 	"crypto/rand"
 	"crypto/sha256"
+	"encoding/binary"
 	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"hash"
+	"io"
 	"os"
 	"strings"
 	"time"
@@ -444,9 +447,11 @@ func (r *Runner) completePreparationWithStructuredOutput(
 	if err != nil {
 		return nil, fmt.Errorf("%w: %w", ErrPromptRender, err)
 	}
+	effectivePrompt := *renderedPrompt
 	if state.directSessionID != "" {
-		renderedPrompt.SessionID = state.directSessionID
+		effectivePrompt.SessionID = state.directSessionID
 	}
+	effectivePrompt.Messages = domain.ConcatRenderedMessages(renderedPrompt.Messages, req.AppendedMessages)
 
 	end := time.Now().UTC()
 	effectiveModel := state.effectiveModel
@@ -462,9 +467,9 @@ func (r *Runner) completePreparationWithStructuredOutput(
 		OutputContract:       state.effectiveContract,
 		StructuredOutput:     structuredOutput,
 		InputHashes:          inputHashes,
-		SessionID:            renderedPrompt.SessionID,
+		SessionID:            effectivePrompt.SessionID,
-		RenderedPromptHash:   hashRenderedPrompt(*renderedPrompt),
+		RenderedPromptHash:   hashRenderedPrompt(effectivePrompt),
-		Messages:             renderedPrompt.Messages,
+		Messages:             effectivePrompt.Messages,
 		StartTime:            state.start,
 		EndTime:              end,
 		DurationMS:           end.Sub(state.start).Milliseconds(),
@@ -714,29 +719,38 @@ func resolveOutputContract(def *domain.PromptDefinition, override *domain.Output
 	return contract, nil
 }
 
+const renderedPromptHashVersion = "promptkit/rendered-prompt/v2\x00"
+
 func hashRenderedPrompt(p domain.RenderedPrompt) string {
-	var b strings.Builder
+	hasher := sha256.New()
-	if p.SessionID != "" {
+	var lengthBuffer [8]byte
-		b.WriteString("session_id=")
+	_, _ = io.WriteString(hasher, renderedPromptHashVersion)
-		b.WriteString(p.SessionID)
+	writeRenderedPromptHashString(hasher, &lengthBuffer, p.SessionID)
-		b.WriteString("\n---\n")
+	writeRenderedPromptHashLength(hasher, &lengthBuffer, len(p.Messages))
+	for _, message := range p.Messages {
+		writeRenderedPromptHashString(hasher, &lengthBuffer, message.Role)
+		writeRenderedPromptHashString(hasher, &lengthBuffer, message.Content)
+		if message.CacheControl == nil {
+			lengthBuffer[0] = 0
+			_, _ = hasher.Write(lengthBuffer[:1])
+			continue
 		}
-	for _, msg := range p.Messages {
+		lengthBuffer[0] = 1
-		b.WriteString(msg.Role)
+		_, _ = hasher.Write(lengthBuffer[:1])
-		b.WriteByte('\n')
+		writeRenderedPromptHashString(hasher, &lengthBuffer, string(message.CacheControl.Type))
-		b.WriteString(msg.Content)
+		writeRenderedPromptHashString(hasher, &lengthBuffer, message.CacheControl.TTL)
-		if msg.CacheControl != nil {
-			b.WriteString("\ncache_control.type=")
-			b.WriteString(string(msg.CacheControl.Type))
-			if msg.CacheControl.TTL != "" {
-				b.WriteString("\ncache_control.ttl=")
-				b.WriteString(msg.CacheControl.TTL)
 	}
-		}
+	return hex.EncodeToString(hasher.Sum(nil))
-		b.WriteString("\n---\n")
+}
-	}
+
-	h := sha256.Sum256([]byte(b.String()))
+func writeRenderedPromptHashLength(hasher hash.Hash, buffer *[8]byte, length int) {
-	return hex.EncodeToString(h[:])
+	binary.BigEndian.PutUint64(buffer[:], uint64(length))
+	_, _ = hasher.Write(buffer[:])
+}
+
+func writeRenderedPromptHashString(hasher hash.Hash, buffer *[8]byte, value string) {
+	writeRenderedPromptHashLength(hasher, buffer, len(value))
+	_, _ = io.WriteString(hasher, value)
 }
 
 func buildOutputArtifact(content string, format domain.OutputFormat) domain.Artifact {

internal/usecase/runner_test.go

@@ -1110,14 +1110,18 @@ func TestDeriveStructuredSchemaName(t *testing.T) {
 	}
 }
 
-func TestHashRenderedPromptIncludesCacheControlWhenPresent(t *testing.T) {
+func TestHashRenderedPromptIncludesEveryContractedField(t *testing.T) {
-	uncached := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
+	base := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
-		{Role: "system", Content: "sys"},
+		{Role: domain.RoleSystem, Content: "sys"},
-		{Role: "user", Content: "usr"},
+		{Role: domain.RoleUser, Content: "usr"},
 	}}
-	wantLegacyHash := hashString("system\nsys\n---\nuser\nusr\n---\n")
+	identical := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
-	if got := hashRenderedPrompt(uncached); got != wantLegacyHash {
+		{Role: domain.RoleSystem, Content: "sys"},
-		t.Fatalf("expected no-cache hash to preserve legacy input, got %q want %q", got, wantLegacyHash)
+		{Role: domain.RoleUser, Content: "usr"},
+	}}
+	baseHash := hashRenderedPrompt(base)
+	if baseHash != hashRenderedPrompt(identical) {
+		t.Fatal("identical rendered prompts must have the same hash")
 	}
 
 	withCache := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
@@ -1129,7 +1133,7 @@ func TestHashRenderedPromptIncludesCacheControlWhenPresent(t *testing.T) {
 				TTL:  "1h",
 			},
 		},
-		{Role: "user", Content: "usr"},
+		{Role: domain.RoleUser, Content: "usr"},
 	}}
 	alsoWithCache := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
 		{
@@ -1140,7 +1144,7 @@ func TestHashRenderedPromptIncludesCacheControlWhenPresent(t *testing.T) {
 				TTL:  "1h",
 			},
 		},
-		{Role: "user", Content: "usr"},
+		{Role: domain.RoleUser, Content: "usr"},
 	}}
 	withoutTTL := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
 		{
@@ -1150,11 +1154,11 @@ func TestHashRenderedPromptIncludesCacheControlWhenPresent(t *testing.T) {
 				Type: domain.CacheControlEphemeral,
 			},
 		},
-		{Role: "user", Content: "usr"},
+		{Role: domain.RoleUser, Content: "usr"},
 	}}
 
 	cachedHash := hashRenderedPrompt(withCache)
-	if cachedHash == hashRenderedPrompt(uncached) {
+	if cachedHash == baseHash {
 		t.Fatal("expected cache control to change rendered prompt hash")
 	}
 	if cachedHash != hashRenderedPrompt(alsoWithCache) {
@@ -1163,6 +1167,29 @@ func TestHashRenderedPromptIncludesCacheControlWhenPresent(t *testing.T) {
 	if cachedHash == hashRenderedPrompt(withoutTTL) {
 		t.Fatal("expected ttl changes to affect rendered prompt hash")
 	}
+
+	variants := []struct {
+		name   string
+		prompt domain.RenderedPrompt
+	}{
+		{name: "role", prompt: domain.RenderedPrompt{Messages: []domain.RenderedMessage{{Role: domain.RoleDeveloper, Content: "sys"}, {Role: domain.RoleUser, Content: "usr"}}}},
+		{name: "content", prompt: domain.RenderedPrompt{Messages: []domain.RenderedMessage{{Role: domain.RoleSystem, Content: "changed"}, {Role: domain.RoleUser, Content: "usr"}}}},
+		{name: "order", prompt: domain.RenderedPrompt{Messages: []domain.RenderedMessage{{Role: domain.RoleUser, Content: "usr"}, {Role: domain.RoleSystem, Content: "sys"}}}},
+		{name: "session", prompt: domain.RenderedPrompt{SessionID: "session", Messages: base.Messages}},
+	}
+	for _, variant := range variants {
+		t.Run(variant.name, func(t *testing.T) {
+			if hashRenderedPrompt(variant.prompt) == baseHash {
+				t.Fatalf("%s did not change the rendered-prompt hash", variant.name)
+			}
+		})
+	}
+
+	oneMessage := domain.RenderedPrompt{Messages: []domain.RenderedMessage{{Role: domain.RoleUser, Content: "x\n---\nassistant\ny"}}}
+	twoMessages := domain.RenderedPrompt{Messages: []domain.RenderedMessage{{Role: domain.RoleUser, Content: "x"}, {Role: domain.RoleAssistant, Content: "y"}}}
+	if hashRenderedPrompt(oneMessage) == hashRenderedPrompt(twoMessages) {
+		t.Fatal("length-framed hashing did not distinguish legacy separator collision")
+	}
 }
 
 func TestHashRenderedPromptIncludesSessionIDWhenPresent(t *testing.T) {
@@ -1204,6 +1231,75 @@ func TestHashRenderedPromptIncludesSessionIDWhenPresent(t *testing.T) {
 	}
 }
 
+func TestRunnerComposesAppendedMessagesIntoEveryRenderedPrompt(t *testing.T) {
+	renderer := &fakeRenderer{rendered: &domain.RenderedPrompt{
+		SessionID: "rendered-session",
+		Messages: []domain.RenderedMessage{
+			{Role: domain.RoleSystem, Content: "ordinary prefix", CacheControl: &domain.CacheControl{Type: domain.CacheControlEphemeral, TTL: "1h"}},
+			{Role: domain.RoleUser, Content: "ordinary request"},
+		},
+	}}
+	client := &fakeLLM{resp: &domain.GenerateResponse{Content: "output"}}
+	runner := NewRunner(
+		&fakePromptRepo{def: promptDef(domain.FormatText, domain.ValidationNone, 0)},
+		&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}},
+		nil,
+		defaultArtifactReader(),
+		renderer,
+		client,
+		nil,
+		nil,
+	)
+	appended := []domain.RenderedMessage{
+		{Role: domain.RoleAssistant, Content: "consumer response"},
+		{Role: domain.RoleUser, Content: "consumer correction", CacheControl: &domain.CacheControl{Type: domain.CacheControlEphemeral}},
+	}
+	request := domain.RunRequest{PromptID: "p", ProfileID: "exec", Inputs: singleInputRef(), AppendedMessages: appended}
+
+	plain, err := runner.Prepare(context.Background(), domain.RunRequest{PromptID: "p", ProfileID: "exec", Inputs: singleInputRef()})
+	if err != nil {
+		t.Fatalf("prepare without appended messages: %v", err)
+	}
+	empty, err := runner.Prepare(context.Background(), domain.RunRequest{PromptID: "p", ProfileID: "exec", Inputs: singleInputRef(), AppendedMessages: []domain.RenderedMessage{}})
+	if err != nil {
+		t.Fatalf("prepare with empty appended messages: %v", err)
+	}
+	if !reflect.DeepEqual(empty.Messages, plain.Messages) || empty.RenderedPromptHash != plain.RenderedPromptHash {
+		t.Fatalf("empty appended messages changed preparation: empty=%#v plain=%#v", empty, plain)
+	}
+	prepared, err := runner.Prepare(context.Background(), request)
+	if err != nil {
+		t.Fatalf("prepare with appended messages: %v", err)
+	}
+	if prepared.PromptHash != plain.PromptHash || prepared.RenderedPromptHash == plain.RenderedPromptHash {
+		t.Fatalf("hashes with appended messages = (%q, %q), plain = (%q, %q)", prepared.PromptHash, prepared.RenderedPromptHash, plain.PromptHash, plain.RenderedPromptHash)
+	}
+
+	expected := []domain.RenderedMessage{
+		{Role: domain.RoleSystem, Content: "ordinary prefix", CacheControl: &domain.CacheControl{Type: domain.CacheControlEphemeral, TTL: "1h"}},
+		{Role: domain.RoleUser, Content: "ordinary request"},
+		{Role: domain.RoleAssistant, Content: "consumer response"},
+		{Role: domain.RoleUser, Content: "consumer correction", CacheControl: &domain.CacheControl{Type: domain.CacheControlEphemeral}},
+	}
+	if !reflect.DeepEqual(prepared.Messages, expected) {
+		t.Fatalf("prepared messages = %#v, want %#v", prepared.Messages, expected)
+	}
+
+	result, err := runner.Run(context.Background(), request)
+	if err != nil {
+		t.Fatalf("run with appended messages: %v", err)
+	}
+	if result.RenderedPromptHash != prepared.RenderedPromptHash || !reflect.DeepEqual(client.lastReq.Prompt.Messages, expected) {
+		t.Fatalf("run did not use the prepared effective prompt: result=%#v request=%#v prepared=%#v", result, client.lastReq.Prompt.Messages, prepared)
+	}
+
+	renderer.rendered.Messages[0].Content = "changed source"
+	appended[1].CacheControl.Type = "changed caller value"
+	if !reflect.DeepEqual(prepared.Messages, expected) {
+		t.Fatalf("prepared messages changed after source or caller mutation: %#v", prepared.Messages)
+	}
+}
+
 func TestRunnerRunSuccessful(t *testing.T) {
 	promptRepo := &fakePromptRepo{def: promptDef(domain.FormatMarkdown, domain.ValidationBasic, 0)}
 	execRepo := &fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}}