feat: allow custom model User-Agent overrides

API.md

@@ -213,7 +213,12 @@ fresh reset event.
 - `GET /api/models` — available models.
 - `GET /api/tools` — registered tool definitions.
 - `GET/POST/PUT/DELETE /api/custom-models[/<id>]` — custom model CRUD.
-- `POST /api/custom-models-test` — test a custom model config.
+  Custom models accept an optional `user_agent` string. When set, Shelley uses
+  it as the outbound `User-Agent` for that model; when empty, Shelley sends its
+  normal `Shelley/<commit>` value.
+- `POST /api/custom-models-test` — test a custom model config. The request also
+  accepts `user_agent`, so client-restricted providers can be tested before the
+  model is saved.
 - `GET/POST/PUT/DELETE /api/notification-channels[/<id>]`,
   `GET /api/notification-channel-types` — notification CRUD.
 

db/query/models.sql

@@ -5,8 +5,8 @@ SELECT * FROM models ORDER BY created_at ASC;
 SELECT * FROM models WHERE model_id = ?;
 
 -- name: CreateModel :one
-INSERT INTO models (model_id, display_name, provider_type, endpoint, api_key, model_name, max_tokens, tags, reasoning_effort, image_support, reasoning_support, reasoning_map)
-VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+INSERT INTO models (model_id, display_name, provider_type, endpoint, api_key, model_name, max_tokens, tags, reasoning_effort, image_support, reasoning_support, reasoning_map, user_agent)
+VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
 RETURNING *;
 
 -- name: UpdateModel :one
@@ -22,6 +22,7 @@ SET display_name = ?,
     image_support = ?,
     reasoning_support = ?,
     reasoning_map = ?,
+    user_agent = ?,
     updated_at = CURRENT_TIMESTAMP
 WHERE model_id = ?
 RETURNING *;

db/schema/033-add-model-user-agent.sql

@@ -0,0 +1 @@
+ALTER TABLE models ADD COLUMN user_agent TEXT NOT NULL DEFAULT '';

llm/llmhttp/llmhttp.go

@@ -25,6 +25,7 @@ const (
 	modelIDKey
 	providerKey
 	requestTraceKey
+	userAgentKey
 )
 
 // shelleyRequestIDHeader is the header Shelley sets on every LLM request with a
@@ -178,6 +179,20 @@ func ProviderFromContext(ctx context.Context) string {
 	return ""
 }
 
+// WithUserAgent returns a context that overrides Shelley's default User-Agent.
+// An empty value preserves the default.
+func WithUserAgent(ctx context.Context, userAgent string) context.Context {
+	return context.WithValue(ctx, userAgentKey, userAgent)
+}
+
+// UserAgentFromContext returns the configured User-Agent override, if any.
+func UserAgentFromContext(ctx context.Context) string {
+	if v := ctx.Value(userAgentKey); v != nil {
+		return v.(string)
+	}
+	return ""
+}
+
 // ErrIdleTimeout is returned (wrapped) when a response stream makes no
 // progress — no bytes received — for longer than the configured idle timeout.
 // Callers can test for it with errors.Is. It is deliberately distinct from
@@ -208,11 +223,14 @@ func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
 	// Clone the request to avoid modifying the original
 	req = req.Clone(req.Context())
 
-	// Add User-Agent with Shelley version
-	info := version.GetInfo()
-	userAgent := "Shelley"
-	if info.Commit != "" {
-		userAgent += "/" + info.Commit[:min(8, len(info.Commit))]
+	// Add the per-model override or Shelley's default User-Agent.
+	userAgent := UserAgentFromContext(req.Context())
+	if userAgent == "" {
+		info := version.GetInfo()
+		userAgent = "Shelley"
+		if info.Commit != "" {
+			userAgent += "/" + info.Commit[:min(8, len(info.Commit))]
+		}
 	}
 	req.Header.Set("User-Agent", userAgent)
 

llm/llmhttp/llmhttp_test.go

@@ -32,6 +32,12 @@ func TestContextFunctions(t *testing.T) {
 		t.Errorf("ProviderFromContext() = %q, want %q", got, "anthropic")
 	}
 
+	// Test User-Agent override
+	ctx = WithUserAgent(ctx, "custom-agent/1.0")
+	if got := UserAgentFromContext(ctx); got != "custom-agent/1.0" {
+		t.Errorf("UserAgentFromContext() = %q, want %q", got, "custom-agent/1.0")
+	}
+
 	// Test empty context
 	emptyCtx := context.Background()
 	if got := ConversationIDFromContext(emptyCtx); got != "" {
@@ -43,6 +49,9 @@ func TestContextFunctions(t *testing.T) {
 	if got := ProviderFromContext(emptyCtx); got != "" {
 		t.Errorf("ProviderFromContext(empty) = %q, want empty", got)
 	}
+	if got := UserAgentFromContext(emptyCtx); got != "" {
+		t.Errorf("UserAgentFromContext(empty) = %q, want empty", got)
+	}
 }
 
 func TestTransportAddsHeaders(t *testing.T) {
@@ -83,6 +92,29 @@ func TestTransportAddsHeaders(t *testing.T) {
 	}
 }
 
+func TestTransportUsesUserAgentOverride(t *testing.T) {
+	var got string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		got = r.Header.Get("User-Agent")
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	ctx := WithUserAgent(context.Background(), "codex_cli_rs/0.144.0")
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, server.URL, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	resp, err := NewClient(nil).Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	resp.Body.Close()
+	if got != "codex_cli_rs/0.144.0" {
+		t.Fatalf("User-Agent = %q, want override", got)
+	}
+}
+
 func TestTransportAddsSessionAffinityForFireworks(t *testing.T) {
 	// Create a test server that echoes request headers
 	var receivedHeaders http.Header

models/models.go

@@ -437,6 +437,7 @@ type serviceEntry struct {
 	source      string
 	displayName string
 	tags        string
+	userAgent   string
 	baseURL     string
 	apiType     APIType
 }
@@ -448,47 +449,55 @@ type ConfigInfo interface {
 
 // loggingService wraps an llm.Service with request/usage logging.
 type loggingService struct {
-	service  llm.Service
-	logger   *slog.Logger
-	modelID  string
-	provider Provider
+	service   llm.Service
+	logger    *slog.Logger
+	modelID   string
+	provider  Provider
+	userAgent string
 }
 
 func (l *loggingService) Do(ctx context.Context, request *llm.Request) (*llm.Response, error) {
 	start := time.Now()
 	ctx = llmhttp.WithModelID(ctx, l.modelID)
 	ctx = llmhttp.WithProvider(ctx, string(l.provider))
+	if l.userAgent != "" {
+		ctx = llmhttp.WithUserAgent(ctx, l.userAgent)
+	}
 	response, err := l.service.Do(ctx, request)
 	durationSeconds := time.Since(start).Seconds()
 
 	if err != nil {
-		logAttrs := []any{"model", l.modelID, "duration_seconds", durationSeconds}
-		if configProvider, ok := l.service.(ConfigInfo); ok {
-			for k, v := range configProvider.ConfigDetails() {
-				logAttrs = append(logAttrs, k, v)
+		if l.logger != nil {
+			logAttrs := []any{"model", l.modelID, "duration_seconds", durationSeconds}
+			if configProvider, ok := l.service.(ConfigInfo); ok {
+				for k, v := range configProvider.ConfigDetails() {
+					logAttrs = append(logAttrs, k, v)
+				}
 			}
+			logAttrs = append(logAttrs, "error", err)
+			l.logger.Error("LLM request failed", logAttrs...)
 		}
-		logAttrs = append(logAttrs, "error", err)
-		l.logger.Error("LLM request failed", logAttrs...)
 		return response, err
 	}
 
-	logAttrs := []any{"model", l.modelID, "duration_seconds", durationSeconds}
-	if !response.Usage.IsZero() {
-		logAttrs = append(
-			logAttrs,
-			"input_tokens", response.Usage.InputTokens,
-			"output_tokens", response.Usage.OutputTokens,
-			"cost_usd", response.Usage.CostUSD,
-		)
-		if response.Usage.CacheCreationInputTokens > 0 {
-			logAttrs = append(logAttrs, "cache_creation_input_tokens", response.Usage.CacheCreationInputTokens)
-		}
-		if response.Usage.CacheReadInputTokens > 0 {
-			logAttrs = append(logAttrs, "cache_read_input_tokens", response.Usage.CacheReadInputTokens)
+	if l.logger != nil {
+		logAttrs := []any{"model", l.modelID, "duration_seconds", durationSeconds}
+		if !response.Usage.IsZero() {
+			logAttrs = append(
+				logAttrs,
+				"input_tokens", response.Usage.InputTokens,
+				"output_tokens", response.Usage.OutputTokens,
+				"cost_usd", response.Usage.CostUSD,
+			)
+			if response.Usage.CacheCreationInputTokens > 0 {
+				logAttrs = append(logAttrs, "cache_creation_input_tokens", response.Usage.CacheCreationInputTokens)
+			}
+			if response.Usage.CacheReadInputTokens > 0 {
+				logAttrs = append(logAttrs, "cache_read_input_tokens", response.Usage.CacheReadInputTokens)
+			}
 		}
+		l.logger.Info("LLM request completed", logAttrs...)
 	}
-	l.logger.Info("LLM request completed", logAttrs...)
 	return response, err
 }
 
@@ -608,6 +617,7 @@ func (m *Manager) loadCustomModelsLocked(dbModels []generated.Model) {
 			source:      SourceCustomLabel,
 			displayName: model.DisplayName,
 			tags:        model.Tags,
+			userAgent:   model.UserAgent,
 		}
 		m.modelOrder = append(m.modelOrder, model.ModelID)
 	}
@@ -660,15 +670,13 @@ func (m *Manager) GetService(modelID string) (llm.Service, error) {
 	if !ok {
 		return nil, fmt.Errorf("unsupported model: %s", modelID)
 	}
-	if m.logger != nil {
-		return &loggingService{
-			service:  entry.service,
-			logger:   m.logger,
-			modelID:  entry.modelID,
-			provider: entry.provider,
-		}, nil
-	}
-	return entry.service, nil
+	return &loggingService{
+		service:   entry.service,
+		logger:    m.logger,
+		modelID:   entry.modelID,
+		provider:  entry.provider,
+		userAgent: entry.userAgent,
+	}, nil
 }
 
 func (m *Manager) GetAvailableModels() []string {