Add custom backend configuration

internal/adapter/cli/run_test.go

@@ -963,6 +963,98 @@ profile_dir: %s
 	}
 }
 
+func TestRenderCommandUsesConfiguredCustomBackend(t *testing.T) {
+	lib := newCLITestLibrary(t)
+	writePromptDefinition(t, lib.promptDir, "custom.yaml", `id: custom
+version: "1"
+default_profile: local-gpu
+messages:
+  - role: user
+    content: "hello"
+output:
+  format: text
+  validation_mode: none
+`)
+	if err := os.WriteFile(filepath.Join(lib.profileDir, "local-gpu.yaml"), []byte(`id: local-gpu
+backend: local-gpu
+model: local-model
+`), 0o644); err != nil {
+		t.Fatalf("write profile fixture: %v", err)
+	}
+	configPath := writeAppConfigFile(t, fmt.Sprintf(`
+prompt_dir: %s
+profile_dir: %s
+backends:
+  local-gpu:
+    endpoint: http://localhost:11434/v1
+    extra_params:
+      provider_option: enabled
+    concurrency_limit: 2
+    queue_capacity: 0
+`, lib.promptDir, lib.profileDir))
+
+	code, _, stderr := runCLICommand(t, renderCommand, []string{
+		"--config", configPath,
+		"--prompt", "custom",
+	})
+	if code != ExitOK {
+		t.Fatalf("expected ExitOK, got %d stderr=%q", code, stderr)
+	}
+}
+
+func TestConfiguredBackendValidationComesFromPromptkit(t *testing.T) {
+	lib := newCLITestLibrary(t)
+
+	for _, tc := range []struct {
+		name    string
+		backend string
+	}{
+		{
+			name: "reserved ID",
+			backend: `openrouter:
+    endpoint: http://localhost:11434/v1`,
+		},
+		{
+			name: "invalid endpoint",
+			backend: `local-gpu:
+    endpoint: not-a-url`,
+		},
+		{
+			name: "invalid capacity relationship",
+			backend: `local-gpu:
+    endpoint: http://localhost:11434/v1
+    queue_capacity: 0`,
+		},
+		{
+			name: "reserved extra parameter",
+			backend: `local-gpu:
+    endpoint: http://localhost:11434/v1
+    extra_params:
+      model: forbidden`,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			configPath := writeAppConfigFile(t, fmt.Sprintf(`
+prompt_dir: %s
+profile_dir: %s
+backends:
+  %s
+`, lib.promptDir, lib.profileDir, tc.backend))
+			cfg, err := parseRenderArgs([]string{"--config", configPath, "--prompt", "custom"})
+			if err != nil {
+				t.Fatalf("expected config decoding to succeed, got %v", err)
+			}
+			_, err = newEngine(cfg.runConfig.engineSettings())
+			if !errors.Is(err, promptkit.ErrInvalidConfig) {
+				t.Fatalf("expected Promptkit ErrInvalidConfig, got %v", err)
+			}
+			if !strings.Contains(err.Error(), "engine initialization from application configuration") {
+				t.Fatalf("expected application context, got %v", err)
+			}
+		})
+	}
+}
+
 func TestRenderCommandExplicitTextFormatWorks(t *testing.T) {
 	lib := newCLITestLibrary(t)
 	inputPath := lib.writeInputFile(t, "transcript.md", "hello transcript")