Preserve cache control in rendered prompts

internal/usecase/runner.go

@@ -428,6 +428,14 @@ func hashRenderedPrompt(p domain.RenderedPrompt) string {
 		b.WriteString(msg.Role)
 		b.WriteByte('\n')
 		b.WriteString(msg.Content)
+		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)
+			}
+		}
 		b.WriteString("\n---\n")
 	}
 	h := sha256.Sum256([]byte(b.String()))

internal/usecase/runner_test.go

@@ -577,6 +577,61 @@ func TestDeriveStructuredSchemaName(t *testing.T) {
 	}
 }
 
+func TestHashRenderedPromptIncludesCacheControlWhenPresent(t *testing.T) {
+	uncached := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
+		{Role: "system", Content: "sys"},
+		{Role: "user", Content: "usr"},
+	}}
+	wantLegacyHash := hashString("system\nsys\n---\nuser\nusr\n---\n")
+	if got := hashRenderedPrompt(uncached); got != wantLegacyHash {
+		t.Fatalf("expected no-cache hash to preserve legacy input, got %q want %q", got, wantLegacyHash)
+	}
+
+	withCache := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
+		{
+			Role:    "system",
+			Content: "sys",
+			CacheControl: &domain.CacheControl{
+				Type: domain.CacheControlEphemeral,
+				TTL:  "1h",
+			},
+		},
+		{Role: "user", Content: "usr"},
+	}}
+	alsoWithCache := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
+		{
+			Role:    "system",
+			Content: "sys",
+			CacheControl: &domain.CacheControl{
+				Type: domain.CacheControlEphemeral,
+				TTL:  "1h",
+			},
+		},
+		{Role: "user", Content: "usr"},
+	}}
+	withoutTTL := domain.RenderedPrompt{Messages: []domain.RenderedMessage{
+		{
+			Role:    "system",
+			Content: "sys",
+			CacheControl: &domain.CacheControl{
+				Type: domain.CacheControlEphemeral,
+			},
+		},
+		{Role: "user", Content: "usr"},
+	}}
+
+	cachedHash := hashRenderedPrompt(withCache)
+	if cachedHash == hashRenderedPrompt(uncached) {
+		t.Fatal("expected cache control to change rendered prompt hash")
+	}
+	if cachedHash != hashRenderedPrompt(alsoWithCache) {
+		t.Fatal("expected identical cache control metadata to produce stable hash")
+	}
+	if cachedHash == hashRenderedPrompt(withoutTTL) {
+		t.Fatal("expected ttl changes to affect rendered prompt hash")
+	}
+}
+
 func TestRunnerRunSuccessful(t *testing.T) {
 	promptRepo := &fakePromptRepo{def: promptDef(domain.FormatMarkdown, domain.ValidationBasic, 0)}
 	execRepo := &fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}}