chore: add experiment toggle for terraform workspace caching (#20559)

Experiments passed to provisioners to determine behavior. This adds
`--experiments` flag to provisioner daemons. Prior to this, provisioners
had no method to turn on/off experiments.

coderd/apidoc/docs.go

@@ -14322,7 +14322,8 @@ const docTemplate = `{
                 "web-push",
                 "oauth2",
                 "mcp-server-http",
-                "workspace-sharing"
+                "workspace-sharing",
+                "terraform-directory-reuse"
             ],
             "x-enum-comments": {
                 "ExperimentAutoFillParameters": "This should not be taken out of experiments until we have redesigned the feature.",
@@ -14330,6 +14331,7 @@ const docTemplate = `{
                 "ExperimentMCPServerHTTP": "Enables the MCP HTTP server functionality.",
                 "ExperimentNotifications": "Sends notifications via SMTP and webhooks following certain events.",
                 "ExperimentOAuth2": "Enables OAuth2 provider functionality.",
+                "ExperimentTerraformWorkspace": "Enables reuse of existing terraform directory for builds",
                 "ExperimentWebPush": "Enables web push notifications through the browser.",
                 "ExperimentWorkspaceSharing": "Enables updating workspace ACLs for sharing with users and groups.",
                 "ExperimentWorkspaceUsage": "Enables the new workspace usage tracking."
@@ -14342,7 +14344,8 @@ const docTemplate = `{
                 "ExperimentWebPush",
                 "ExperimentOAuth2",
                 "ExperimentMCPServerHTTP",
-                "ExperimentWorkspaceSharing"
+                "ExperimentWorkspaceSharing",
+                "ExperimentTerraformWorkspace"
             ]
         },
         "codersdk.ExternalAPIKeyScopes": {

coderd/apidoc/swagger.json

@@ -12929,7 +12929,8 @@
 				"web-push",
 				"oauth2",
 				"mcp-server-http",
-				"workspace-sharing"
+				"workspace-sharing",
+				"terraform-directory-reuse"
 			],
 			"x-enum-comments": {
 				"ExperimentAutoFillParameters": "This should not be taken out of experiments until we have redesigned the feature.",
@@ -12937,6 +12938,7 @@
 				"ExperimentMCPServerHTTP": "Enables the MCP HTTP server functionality.",
 				"ExperimentNotifications": "Sends notifications via SMTP and webhooks following certain events.",
 				"ExperimentOAuth2": "Enables OAuth2 provider functionality.",
+				"ExperimentTerraformWorkspace": "Enables reuse of existing terraform directory for builds",
 				"ExperimentWebPush": "Enables web push notifications through the browser.",
 				"ExperimentWorkspaceSharing": "Enables updating workspace ACLs for sharing with users and groups.",
 				"ExperimentWorkspaceUsage": "Enables the new workspace usage tracking."
@@ -12949,7 +12951,8 @@
 				"ExperimentWebPush",
 				"ExperimentOAuth2",
 				"ExperimentMCPServerHTTP",
-				"ExperimentWorkspaceSharing"
+				"ExperimentWorkspaceSharing",
+				"ExperimentTerraformWorkspace"
 			]
 		},
 		"codersdk.ExternalAPIKeyScopes": {

coderd/coderd.go

@@ -1999,6 +1999,7 @@ func (api *API) CreateInMemoryTaggedProvisionerDaemon(dialCtx context.Context, n
 		api.NotificationsEnqueuer,
 		&api.PrebuildsReconciler,
 		api.ProvisionerdServerMetrics,
+		api.Experiments,
 	)
 	if err != nil {
 		return nil, err

coderd/provisionerdserver/provisionerdserver.go

@@ -121,6 +121,7 @@ type server struct {
 	NotificationsEnqueuer       notifications.Enqueuer
 	PrebuildsOrchestrator       *atomic.Pointer[prebuilds.ReconciliationOrchestrator]
 	UsageInserter               *atomic.Pointer[usage.Inserter]
+	Experiments                 codersdk.Experiments
 
 	OIDCConfig promoauth.OAuth2Config
 
@@ -182,6 +183,7 @@ func NewServer(
 	enqueuer notifications.Enqueuer,
 	prebuildsOrchestrator *atomic.Pointer[prebuilds.ReconciliationOrchestrator],
 	metrics *Metrics,
+	experiments codersdk.Experiments,
 ) (proto.DRPCProvisionerDaemonServer, error) {
 	// Fail-fast if pointers are nil
 	if lifecycleCtx == nil {
@@ -253,6 +255,7 @@ func NewServer(
 		PrebuildsOrchestrator:       prebuildsOrchestrator,
 		UsageInserter:               usageInserter,
 		metrics:                     metrics,
+		Experiments:                 experiments,
 	}
 
 	if s.heartbeatFn == nil {

coderd/provisionerdserver/provisionerdserver_test.go

@@ -26,6 +26,7 @@ import (
 	"storj.io/drpc"
 
 	"cdr.dev/slog/sloggers/slogtest"
+	"github.com/coder/coder/v2/coderd"
 	"github.com/coder/coder/v2/coderd/util/ptr"
 	"github.com/coder/quartz"
 	"github.com/coder/serpent"
@@ -4162,7 +4163,7 @@ func setup(t *testing.T, ignoreLogErrors bool, ov *overrides) (proto.DRPCProvisi
 	defOrg, err := db.GetDefaultOrganization(context.Background())
 	require.NoError(t, err, "default org not found")
 
-	deploymentValues := &codersdk.DeploymentValues{}
+	deploymentValues := coderdtest.DeploymentValues(t)
 	var externalAuthConfigs []*externalauth.Config
 	tss := testTemplateScheduleStore()
 	uqhss := testUserQuietHoursScheduleStore()
@@ -4285,6 +4286,7 @@ func setup(t *testing.T, ignoreLogErrors bool, ov *overrides) (proto.DRPCProvisi
 		notifEnq,
 		&op,
 		provisionerdserver.NewMetrics(logger),
+		coderd.ReadExperiments(logger, deploymentValues.Experiments),
 	)
 	require.NoError(t, err)
 	return srv, db, ps, daemon