config: make WorkerRootPath a derived method, not a parsed field

Addresses review feedback: WorkerRootPath isn't something a user
provides, so it doesn't belong in Config as a settable/parsed field
(and isn't documented in config/README.md). Move the
<workspaces_root_path>/.workers derivation into a ServiceConfig method
with its own test, so it can't drift from what's documented on
WorkspacesRootPath, and Parse no longer computes or stores it.

Author: yushan8

config/config_test.go

@@ -70,41 +70,11 @@ repository:
 	}
 }
 
-func TestParse_ServiceDefaults(t *testing.T) {
-	tests := []struct {
-		name               string
-		give               string
-		wantWorkerRootPath string
-	}{
-		{
-			name: "worker_root_path defaults when unset",
-			give: _baseServiceYAML + `
-repository:
-  - remote: "r1"
-`,
-			wantWorkerRootPath: filepath.Join("/tmp/x", ".workers"),
-		},
-		{
-			name: "worker_root_path explicit value preserved",
-			give: `
-service:
-  workspaces_root_path: "/tmp/x"
-  worker_root_path: "/tmp/custom-workers"
-  max_worker_pool_size: 1
-repository:
-  - remote: "r1"
-`,
-			wantWorkerRootPath: "/tmp/custom-workers",
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			cfg, err := Parse(writeConfig(t, tt.give))
-			require.NoError(t, err)
-			assert.Equal(t, tt.wantWorkerRootPath, cfg.Service.WorkerRootPath)
-		})
-	}
+func TestServiceConfig_WorkerRootPath(t *testing.T) {
+	// Guards the layout documented on ServiceConfig.WorkspacesRootPath:
+	// <workspaces_root_path>/.workers for worker checkouts.
+	svc := ServiceConfig{WorkspacesRootPath: "/tmp/x"}
+	assert.Equal(t, filepath.Join("/tmp/x", ".workers"), svc.WorkerRootPath())
 }
 
 func TestParse_RepositoryDefaults(t *testing.T) {

config/service_config.go

@@ -14,6 +14,8 @@
 
 package config
 
+import "path/filepath"
+
 // ServiceConfig holds operational configuration for the Tango service.
 type ServiceConfig struct {
 	// MaxWorkerPoolSize is the max number of concurrent requests per repository.
@@ -26,10 +28,14 @@ type ServiceConfig struct {
 	// worker checkouts.
 	WorkspacesRootPath string      `yaml:"workspaces_root_path"`
 	Streaming          ChunkConfig `yaml:"streaming"` // streaming chunk sizes; zero values fall back to package defaults
+}
 
-	// WorkerRootPath is the root directory for worker workspace checkouts,
-	// set by Parse to <workspaces_root_path>/.workers. Not settable via YAML.
-	WorkerRootPath string `yaml:"-"`
+// WorkerRootPath returns the root directory for worker workspace checkouts, as
+// documented on WorkspacesRootPath: <workspaces_root_path>/.workers. It is a
+// derived value, not something a user provides, so it's a method rather than
+// a parsed field.
+func (s ServiceConfig) WorkerRootPath() string {
+	return filepath.Join(s.WorkspacesRootPath, ".workers")
 }
 
 // ChunkConfig controls the number of entries per gRPC stream message.

example/main.go

@@ -72,7 +72,7 @@ func run() error {
 
 	// Repo manager and orchestrator
 	repoManagerClonePath := cfg.Service.WorkspacesRootPath
-	workerRootPath := cfg.Service.WorkerRootPath
+	workerRootPath := cfg.Service.WorkerRootPath()
 	if err := os.MkdirAll(repoManagerClonePath, 0o755); err != nil {
 		return fmt.Errorf("failed to create repo manager clone path: %w", err)
 	}