backend: require OLLIE_BACKEND/OLLIE_MODEL; no silent ollama default

- NewWithName and newFromEnv now error when OLLIE_BACKEND is unset
  instead of falling back to ollama silently
- createSession reads OLLIE_MODEL as fallback when model= is not given
- Update test to assert error on missing OLLIE_BACKEND

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pkg/backend/new.go

@@ -59,13 +59,13 @@ func New() (Backend, error) {
 
 // NewWithName constructs a Backend for the given backend name, loading
 // env-file defaults for API keys/URLs but ignoring OLLIE_BACKEND.
-// If name is empty, falls back to OLLIE_BACKEND / "ollama".
+// If name is empty, falls back to OLLIE_BACKEND; errors if neither is set.
 func NewWithName(name string) (Backend, error) {
 	loadEnvFile(paths.CfgDir() + "/env")
 	if name == "" {
 		name = os.Getenv("OLLIE_BACKEND")
 		if name == "" {
-			name = "ollama"
+			return nil, fmt.Errorf("no backend specified: set OLLIE_BACKEND or pass backend= to the session")
 		}
 	}
 	return newBackend(name)
@@ -76,7 +76,7 @@ func newFromEnv(envFile string) (Backend, error) {
 
 	which := os.Getenv("OLLIE_BACKEND")
 	if which == "" {
-		which = "ollama"
+		return nil, fmt.Errorf("OLLIE_BACKEND is not set")
 	}
 
 	return newBackend(which)

pkg/backend/new_test.go

@@ -31,14 +31,11 @@ func clearEnv(t *testing.T, keys ...string) {
 	}
 }
 
-func TestNewFromEnv_DefaultOllama(t *testing.T) {
+func TestNewFromEnv_NoBackendErrors(t *testing.T) {
 	clearEnv(t, "OLLIE_BACKEND", "OLLIE_OLLAMA_URL")
-	b, err := newFromEnv("/nonexistent")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if b.Name() != "ollama" {
-		t.Errorf("name = %q; want ollama", b.Name())
+	_, err := newFromEnv("/nonexistent")
+	if err == nil {
+		t.Fatal("expected error when OLLIE_BACKEND is unset, got nil")
 	}
 }
 

pkg/store/session.go

@@ -357,6 +357,9 @@ func (s *SessionStore) createSession(args []string) error {
 			return fmt.Errorf("backend: %w", err)
 		}
 
+		if modelOverride == "" {
+			modelOverride = os.Getenv("OLLIE_MODEL")
+		}
 		if modelOverride != "" {
 			be.SetModel(modelOverride)
 		}