feat: track ai seat usage (#22682)

When a user uses an AI feature, we record them in the `ai_seat_state` as consuming a seat. 

Added in debouching to prevent excessive writes to the db for this feature. There is no need for frequent updates.

coderd/provisionerdserver/provisionerdserver.go

@@ -28,6 +28,7 @@ import (
 	protobuf "google.golang.org/protobuf/proto"
 
 	"cdr.dev/slog/v3"
+	"github.com/coder/coder/v2/coderd/aiseats"
 	"github.com/coder/coder/v2/coderd/apikey"
 	"github.com/coder/coder/v2/coderd/audit"
 	"github.com/coder/coder/v2/coderd/database"
@@ -76,6 +77,7 @@ const (
 type Options struct {
 	OIDCConfig          promoauth.OAuth2Config
 	ExternalAuthConfigs []*externalauth.Config
+	AISeatTracker       aiseats.SeatTracker
 
 	// Clock for testing
 	Clock quartz.Clock
@@ -120,6 +122,7 @@ type server struct {
 	NotificationsEnqueuer       notifications.Enqueuer
 	PrebuildsOrchestrator       *atomic.Pointer[prebuilds.ReconciliationOrchestrator]
 	UsageInserter               *atomic.Pointer[usage.Inserter]
+	AISeatTracker               aiseats.SeatTracker
 	Experiments                 codersdk.Experiments
 
 	OIDCConfig promoauth.OAuth2Config
@@ -215,6 +218,9 @@ func NewServer(
 	if err := tags.Valid(); err != nil {
 		return nil, xerrors.Errorf("invalid tags: %w", err)
 	}
+	if options.AISeatTracker == nil {
+		options.AISeatTracker = aiseats.Noop{}
+	}
 	if options.AcquireJobLongPollDur == 0 {
 		options.AcquireJobLongPollDur = DefaultAcquireJobLongPollDur
 	}
@@ -253,6 +259,7 @@ func NewServer(
 		heartbeatFn:                 options.HeartbeatFn,
 		PrebuildsOrchestrator:       prebuildsOrchestrator,
 		UsageInserter:               usageInserter,
+		AISeatTracker:               options.AISeatTracker,
 		metrics:                     metrics,
 		Experiments:                 experiments,
 	}
@@ -2437,6 +2444,12 @@ func (s *server) completeWorkspaceBuildJob(ctx context.Context, job database.Pro
 		})
 	}
 
+	// Record AI seat usage for successful task workspace builds.
+	if workspaceBuild.Transition == database.WorkspaceTransitionStart && workspace.TaskID.Valid {
+		s.AISeatTracker.RecordUsage(ctx, workspace.OwnerID,
+			aiseats.ReasonTask("task workspace build succeeded"))
+	}
+
 	if s.PrebuildsOrchestrator != nil && input.PrebuiltWorkspaceBuildStage == sdkproto.PrebuiltWorkspaceBuildStage_CLAIM {
 		// Track resource replacements, if there are any.
 		orchestrator := s.PrebuildsOrchestrator.Load()