diff --git a/buildengine/engine.go b/buildengine/engine.go
index c29920769b..e6d398b365 100644
--- a/buildengine/engine.go
+++ b/buildengine/engine.go
@@ -48,7 +48,7 @@ func (b BuildStartedListenerFunc) OnBuildStarted(project Project) { b(project) }
 // Engine for building a set of modules.
 type Engine struct {
 	client           ftlv1connect.ControllerServiceClient
-	projectMetas     map[ProjectKey]projectMeta
+	projectMetas     *xsync.MapOf[ProjectKey, projectMeta]
 	moduleDirs       []string
 	externalDirs     []string
 	controllerSchema *xsync.MapOf[string, *schema.Module]
@@ -87,7 +87,7 @@ func New(ctx context.Context, client ftlv1connect.ControllerServiceClient, modul
 		client:           client,
 		moduleDirs:       moduleDirs,
 		externalDirs:     externalDirs,
-		projectMetas:     map[ProjectKey]projectMeta{},
+		projectMetas:     xsync.NewMapOf[ProjectKey, projectMeta](),
 		controllerSchema: xsync.NewMapOf[string, *schema.Module](),
 		schemaChanges:    pubsub.New[schemaChange](),
 		parallelism:      runtime.NumCPU(),
@@ -109,7 +109,7 @@ func New(ctx context.Context, client ftlv1connect.ControllerServiceClient, modul
 		if err != nil {
 			return nil, err
 		}
-		e.projectMetas[project.Config().Key] = projectMeta{project: project}
+		e.projectMetas.Store(project.Config().Key, projectMeta{project: project})
 		e.projectsToBuild.Store(project.Config().Key, true)
 	}
 
@@ -172,7 +172,10 @@ func (e *Engine) Close() error {
 func (e *Engine) Graph(projects ...ProjectKey) (map[string][]string, error) {
 	out := map[string][]string{}
 	if len(projects) == 0 {
-		projects = maps.Keys(e.projectMetas)
+		e.projectMetas.Range(func(key ProjectKey, _ projectMeta) bool {
+			projects = append(projects, key)
+			return true
+		})
 	}
 	for _, key := range projects {
 		if err := e.buildGraph(string(key), out); err != nil {
@@ -184,7 +187,7 @@ func (e *Engine) Graph(projects ...ProjectKey) (map[string][]string, error) {
 
 func (e *Engine) buildGraph(key string, out map[string][]string) error {
 	var deps []string
-	if meta, ok := e.projectMetas[ProjectKey(key)]; ok {
+	if meta, ok := e.projectMetas.Load(ProjectKey(key)); ok {
 		deps = meta.project.Config().Dependencies
 	} else if sch, ok := e.controllerSchema.Load(key); ok {
 		deps = sch.Imports()
@@ -272,8 +275,8 @@ func (e *Engine) watchForModuleChanges(ctx context.Context, period time.Duration
 			switch event := event.(type) {
 			case WatchEventProjectAdded:
 				config := event.Project.Config()
-				if _, exists := e.projectMetas[config.Key]; !exists {
-					e.projectMetas[config.Key] = projectMeta{project: event.Project}
+				if _, exists := e.projectMetas.Load(config.Key); !exists {
+					e.projectMetas.Store(config.Key, projectMeta{project: event.Project})
 					err := e.buildAndDeploy(ctx, 1, true, config.Key)
 					if err != nil {
 						logger.Errorf(err, "deploy %s failed", config.Key)
@@ -287,13 +290,18 @@ func (e *Engine) watchForModuleChanges(ctx context.Context, period time.Duration
 						logger.Errorf(err, "terminate %s failed", module.Module)
 					}
 				}
-				delete(e.projectMetas, config.Key)
+				e.projectMetas.Delete(config.Key)
 			case WatchEventProjectChanged:
 				config := event.Project.Config()
 
-				lastBuildTime := e.projectMetas[config.Key].lastBuildStartTime
-				if event.Time.Before(lastBuildTime) {
-					logger.Warnf("Skipping build and deploy; event time %v is before the last build time %v", event.Time, lastBuildTime)
+				meta, ok := e.projectMetas.Load(config.Key)
+				if !ok {
+					logger.Warnf("project %q not found", config.Key)
+					continue
+				}
+
+				if event.Time.Before(meta.lastBuildStartTime) {
+					logger.Debugf("Skipping build and deploy; event time %v is before the last build time %v", event.Time, meta.lastBuildStartTime)
 					continue // Skip this event as it's outdated
 				}
 				err := e.buildAndDeploy(ctx, 1, true, config.Key)
@@ -349,20 +357,24 @@ func computeModuleHash(module *schema.Module) ([]byte, error) {
 
 func (e *Engine) getDependentProjectKeys(name string) []ProjectKey {
 	dependentProjectKeys := map[ProjectKey]bool{}
-	for k, meta := range e.projectMetas {
+	e.projectMetas.Range(func(key ProjectKey, meta projectMeta) bool {
 		for _, dep := range meta.project.Config().Dependencies {
 			if dep == name {
-				dependentProjectKeys[k] = true
+				dependentProjectKeys[key] = true
 			}
 		}
-	}
+		return true
+	})
 	return maps.Keys(dependentProjectKeys)
 }
 
 func (e *Engine) buildAndDeploy(ctx context.Context, replicas int32, waitForDeployOnline bool, projects ...ProjectKey) error {
 	logger := log.FromContext(ctx)
 	if len(projects) == 0 {
-		projects = maps.Keys(e.projectMetas)
+		e.projectMetas.Range(func(key ProjectKey, meta projectMeta) bool {
+			projects = append(projects, key)
+			return true
+		})
 	}
 
 	buildGroup := errgroup.Group{}
@@ -412,10 +424,13 @@ type buildCallback func(ctx context.Context, project Project) error
 func (e *Engine) buildWithCallback(ctx context.Context, callback buildCallback, projects ...ProjectKey) error {
 	mustBuild := map[ProjectKey]bool{}
 	if len(projects) == 0 {
-		projects = maps.Keys(e.projectMetas)
+		e.projectMetas.Range(func(key ProjectKey, meta projectMeta) bool {
+			projects = append(projects, key)
+			return true
+		})
 	}
 	for _, key := range projects {
-		meta, ok := e.projectMetas[key]
+		meta, ok := e.projectMetas.Load(key)
 		if !ok {
 			return fmt.Errorf("project %q not found", key)
 		}
@@ -425,7 +440,7 @@ func (e *Engine) buildWithCallback(ctx context.Context, callback buildCallback,
 		if err != nil {
 			return err
 		}
-		e.projectMetas[key] = projectMeta{project: project}
+		e.projectMetas.Store(key, projectMeta{project: project})
 		mustBuild[key] = true
 	}
 	graph, err := e.Graph(projects...)
@@ -488,7 +503,7 @@ func (e *Engine) tryBuild(ctx context.Context, mustBuild map[ProjectKey]bool, ke
 		return e.mustSchema(ctx, key, builtModules, schemas)
 	}
 
-	meta, ok := e.projectMetas[key]
+	meta, ok := e.projectMetas.Load(key)
 	if !ok {
 		return fmt.Errorf("project %q not found", key)
 	}
@@ -501,10 +516,10 @@ func (e *Engine) tryBuild(ctx context.Context, mustBuild map[ProjectKey]bool, ke
 	}
 
 	meta.lastBuildStartTime = time.Now()
-	e.projectMetas[key] = meta
+	e.projectMetas.Store(key, meta)
 	err := e.build(ctx, key, builtModules, schemas)
 	if err == nil && callback != nil {
-		return callback(ctx, e.projectMetas[key].project)
+		return callback(ctx, meta.project)
 	}
 
 	return err
@@ -523,7 +538,7 @@ func (e *Engine) mustSchema(ctx context.Context, key ProjectKey, builtModules ma
 //
 // Assumes that all dependencies have been built and are available in "built".
 func (e *Engine) build(ctx context.Context, key ProjectKey, builtModules map[string]*schema.Module, schemas chan<- *schema.Module) error {
-	meta, ok := e.projectMetas[key]
+	meta, ok := e.projectMetas.Load(key)
 	if !ok {
 		return fmt.Errorf("project %q not found", key)
 	}
@@ -557,14 +572,14 @@ func (e *Engine) gatherSchemas(
 	project Project,
 	out map[string]*schema.Module,
 ) error {
-	latestModule, ok := e.projectMetas[project.Config().Key]
+	latestModule, ok := e.projectMetas.Load(project.Config().Key)
 	if !ok {
 		latestModule = projectMeta{project: project}
 	}
 	for _, dep := range latestModule.project.Config().Dependencies {
 		out[dep] = moduleSchemas[dep]
 		if dep != "builtin" {
-			depModule, ok := e.projectMetas[ProjectKey(dep)]
+			depModule, ok := e.projectMetas.Load(ProjectKey(dep))
 			// TODO: should we be gathering schemas from dependencies without a project?
 			// This can happen if the schema is loaded from the controller
 			if ok {