diff --git a/internal/adapter/cli/run.go b/internal/adapter/cli/run.go
index 00af7af..6079252 100644
--- a/internal/adapter/cli/run.go
+++ b/internal/adapter/cli/run.go
@@ -206,7 +206,7 @@ func serveCommand(args []string, stderr io.Writer) int {
 	srv := &http.Server{
 		Addr:              cfg.addr,
 		Handler:           h,
-		ReadHeaderTimeout: 10 * time.Second,
+		ReadHeaderTimeout: defaults.HTTPReadHeaderTimeoutDefault,
 	}
 
 	fmt.Fprintf(stderr, "serving on %s\n", cfg.addr)
@@ -397,5 +397,5 @@ func printSummary(stderr io.Writer, res *domain.RunResult) {
 func printUsage(w io.Writer) {
 	fmt.Fprintln(w, "usage: scriptorium <run|serve> ...")
 	fmt.Fprintln(w, "  run:   scriptorium run --prompt-dir DIR --profile-dir DIR --prompt ID --input name=path [--input ...] [--profile ID] [--llm-base-url URL] [--model NAME] [--api-key-env ENV] [--temperature N] [--max-tokens N] [--top-p N] [--var k=v] [--out path] [--timeout 10m]")
-	fmt.Fprintln(w, "  serve: scriptorium serve --addr :8080 --prompt-dir DIR --profile-dir DIR [--llm-base-url URL] [--schema-dir DIR] [--model NAME] [--timeout 10m]")
+	fmt.Fprintf(w, "  serve: scriptorium serve --addr %s --prompt-dir DIR --profile-dir DIR [--llm-base-url URL] [--schema-dir DIR] [--model NAME] [--timeout 10m]\n", defaults.HTTPAddrDefault)
 }
diff --git a/internal/artifact/reader.go b/internal/artifact/reader.go
index 1337359..5863316 100644
--- a/internal/artifact/reader.go
+++ b/internal/artifact/reader.go
@@ -5,6 +5,7 @@ import (
 	"crypto/sha256"
 	"errors"
 	"fmt"
+	"gitea.maximumdirect.net/eric/scriptorium/internal/defaults"
 	"gitea.maximumdirect.net/eric/scriptorium/internal/domain"
 	"mime"
 	"os"
@@ -67,7 +68,7 @@ func (r *inlineReader) Read(ctx context.Context, ref domain.ArtifactRef) (*domai
 
 	body := []byte(ref.Body)
 	return &domain.Artifact{
-		ContentType: "text/plain",
+		ContentType: defaults.ContentTypeTextPlain,
 		Body:        body,
 		Size:        int64(len(body)),
 		Hash:        fmt.Sprintf("%x", sha256.Sum256(body)),
@@ -95,7 +96,7 @@ func (r *fileReader) Read(ctx context.Context, ref domain.ArtifactRef) (*domain.
 
 	contentType := mime.TypeByExtension(filepath.Ext(ref.URI))
 	if contentType == "" {
-		contentType = "text/plain" // Default
+		contentType = defaults.ContentTypeTextPlain
 	}
 
 	return &domain.Artifact{
diff --git a/internal/defaults/defaults.go b/internal/defaults/defaults.go
index 9dc8803..c0d8c85 100644
--- a/internal/defaults/defaults.go
+++ b/internal/defaults/defaults.go
@@ -13,6 +13,7 @@ const (
 	ContentTypeTextPlain       = "text/plain"
 	ContentTypeTextMarkdown    = "text/markdown"
 	ContentTypeApplicationJSON = "application/json"
+	OpenAIChatCompletionsPath  = "/chat/completions"
 
 	ExecutionDefaultTemperature    = 0.0
 	ExecutionDefaultMaxTokens      = 0
@@ -21,7 +22,8 @@ const (
 )
 
 var (
-	LLMRequestTimeoutDefault = 10 * time.Minute
+	LLMRequestTimeoutDefault     = 10 * time.Minute
+	HTTPReadHeaderTimeoutDefault = 10 * time.Second
 )
 
 func ExecutionTargetDefault() domain.ExecutionTarget {
diff --git a/internal/llm/openai_compatible_client.go b/internal/llm/openai_compatible_client.go
index 5e98ffe..c80bb2d 100644
--- a/internal/llm/openai_compatible_client.go
+++ b/internal/llm/openai_compatible_client.go
@@ -90,7 +90,7 @@ func (c *OpenAICompatibleClient) Generate(ctx context.Context, req domain.Genera
 	if endpoint == "" {
 		return nil, fmt.Errorf("%w: endpoint is required", ErrInvalidRequest)
 	}
-	endpoint = strings.TrimRight(endpoint, "/") + "/chat/completions"
+	endpoint = strings.TrimRight(endpoint, "/") + defaults.OpenAIChatCompletionsPath
 
 	wireReq := openAIChatRequest{
 		Model: model,
diff --git a/internal/usecase/runner_test.go b/internal/usecase/runner_test.go
index 1dc37fe..a6d9a40 100644
--- a/internal/usecase/runner_test.go
+++ b/internal/usecase/runner_test.go
@@ -10,6 +10,7 @@ import (
 	"strings"
 	"testing"
 
+	"gitea.maximumdirect.net/eric/scriptorium/internal/defaults"
 	"gitea.maximumdirect.net/eric/scriptorium/internal/domain"
 	"gitea.maximumdirect.net/eric/scriptorium/internal/validate"
 )
@@ -164,6 +165,12 @@ func TestRunnerRunSuccessful(t *testing.T) {
 	if res.EffectiveModelParams.Model != "m" || res.Endpoint != "http://override/v1" {
 		t.Fatalf("unexpected model params: %+v", res.EffectiveModelParams)
 	}
+	if res.Artifact.Name != defaults.OutputArtifactName {
+		t.Fatalf("expected default output artifact name %q, got %q", defaults.OutputArtifactName, res.Artifact.Name)
+	}
+	if res.Artifact.ContentType != defaults.ContentTypeTextMarkdown {
+		t.Fatalf("expected markdown content type %q, got %q", defaults.ContentTypeTextMarkdown, res.Artifact.ContentType)
+	}
 	if res.RawOutput != "# recap" {
 		t.Fatalf("expected raw output, got %q", res.RawOutput)
 	}
@@ -323,6 +330,36 @@ func TestRunnerRunSelectedProfileBeatsBuiltInDefault(t *testing.T) {
 	}
 }
 
+func TestRunnerRunBuiltInDefaultsUsedWhenProfileOmitsOptionalFields(t *testing.T) {
+	promptRepo := &fakePromptRepo{def: promptDef(domain.FormatText, domain.ValidationNone, 0)}
+	execRepo := &fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{
+		"exec": {ID: "exec", Endpoint: "http://profile/v1", Model: "profile-model"},
+	}}
+	llmClient := &fakeLLM{resp: &domain.GenerateResponse{Content: "ok"}}
+	runner := NewRunner(promptRepo, execRepo, defaultArtifactReader(), defaultRenderer(), llmClient, nil)
+
+	res, err := runner.Run(context.Background(), domain.RunRequest{
+		PromptID:  "p",
+		ProfileID: "exec",
+		Inputs:    singleInputRef(),
+	})
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if res.EffectiveModelParams.Temperature != defaults.ExecutionDefaultTemperature {
+		t.Fatalf("expected default temperature %v, got %v", defaults.ExecutionDefaultTemperature, res.EffectiveModelParams.Temperature)
+	}
+	if res.EffectiveModelParams.TopP != defaults.ExecutionDefaultTopP {
+		t.Fatalf("expected default top_p %v, got %v", defaults.ExecutionDefaultTopP, res.EffectiveModelParams.TopP)
+	}
+	if res.EffectiveModelParams.MaxTokens != defaults.ExecutionDefaultMaxTokens {
+		t.Fatalf("expected default max_tokens %d, got %d", defaults.ExecutionDefaultMaxTokens, res.EffectiveModelParams.MaxTokens)
+	}
+	if res.EffectiveModelParams.TimeoutSeconds != defaults.ExecutionDefaultTimeoutSeconds {
+		t.Fatalf("expected default timeout_seconds %d, got %d", defaults.ExecutionDefaultTimeoutSeconds, res.EffectiveModelParams.TimeoutSeconds)
+	}
+}
+
 func TestRunnerRunAPIKeyEnvResolvesFromEnvironment(t *testing.T) {
 	t.Setenv("SCRIPTORIUM_TEST_API_KEY", "secret")
 	promptRepo := &fakePromptRepo{def: promptDef(domain.FormatText, domain.ValidationNone, 0)}
@@ -506,6 +543,30 @@ func TestRunnerRunStructuredRepairRemainsBoundedAndUsesEffectiveModelSettings(t
 	}
 }
 
+func TestBuildOutputArtifactDefaults(t *testing.T) {
+	tests := []struct {
+		name        string
+		format      domain.OutputFormat
+		contentType string
+	}{
+		{name: "text", format: domain.FormatText, contentType: defaults.ContentTypeTextPlain},
+		{name: "markdown", format: domain.FormatMarkdown, contentType: defaults.ContentTypeTextMarkdown},
+		{name: "json", format: domain.FormatJSON, contentType: defaults.ContentTypeApplicationJSON},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			art := buildOutputArtifact("body", tc.format)
+			if art.Name != defaults.OutputArtifactName {
+				t.Fatalf("expected artifact name %q, got %q", defaults.OutputArtifactName, art.Name)
+			}
+			if art.ContentType != tc.contentType {
+				t.Fatalf("expected content type %q, got %q", tc.contentType, art.ContentType)
+			}
+		})
+	}
+}
+
 func promptDef(format domain.OutputFormat, mode domain.ValidationMode, attempts int) *domain.PromptDefinition {
 	return &domain.PromptDefinition{
 		ID:             "p",