feat: add experimental agents support (#22290)

feat: add AI chat system with agent tools and chat UI

Introduce the chatd subsystem and Agents UI for AI-powered chat
within Coder workspaces.

- Add chatd package with chat loop, message compaction, prompt
  management, and LLM provider integration (OpenAI, Anthropic)
- Add agent tools: create workspace, list/read templates, read/write/
  edit files, execute commands
- Add chat API endpoints with streaming, message editing, and
  durable reconnection
- Add database schema and migrations for chats, chat messages, chat
  providers, and chat model configs
- Add RBAC policies and dbauthz enforcement for chat resources
- Add Agents UI pages with conversation timeline, queued messages
  list, diff viewer, and model configuration panel
- Add comprehensive test coverage including coderd integration tests,
  chatd unit tests, and Storybook stories
- Gate feature behind experiments flag

---------

Co-authored-by: Cian Johnston <cian@coder.com>
Co-authored-by: Danielle Maywood <danielle@themaywoods.com>
Co-authored-by: Jeremy Ruppel <jeremy@coder.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

coderd/coderd.go

@@ -49,6 +49,7 @@ import (
 	"github.com/coder/coder/v2/coderd/audit"
 	"github.com/coder/coder/v2/coderd/awsidentity"
 	"github.com/coder/coder/v2/coderd/boundaryusage"
+	"github.com/coder/coder/v2/coderd/chatd"
 	"github.com/coder/coder/v2/coderd/connectionlog"
 	"github.com/coder/coder/v2/coderd/cryptokeys"
 	"github.com/coder/coder/v2/coderd/database"
@@ -238,6 +239,9 @@ type Options struct {
 	SSHConfig codersdk.SSHConfigResponse
 
 	HTTPClient *http.Client
+	// ChatRemotePartsProvider provides cross-replica message_part streaming.
+	// Set by enterprise for HA deployments. Nil in AGPL single-replica.
+	ChatRemotePartsProvider chatd.RemotePartsProvider
 
 	UpdateAgentMetrics func(ctx context.Context, labels prometheusmetrics.AgentMetricLabels, metrics []*agentproto.Stats_Metric)
 	StatsBatcher       workspacestats.Batcher
@@ -588,7 +592,6 @@ func New(options *Options) *API {
 	var buildUsageChecker atomic.Pointer[wsbuilder.UsageChecker]
 	var noopUsageChecker wsbuilder.UsageChecker = wsbuilder.NoopUsageChecker{}
 	buildUsageChecker.Store(&noopUsageChecker)
-
 	api := &API{
 		ctx:          ctx,
 		cancel:       cancel,
@@ -754,6 +757,17 @@ func New(options *Options) *API {
 		panic("failed to setup server tailnet: " + err.Error())
 	}
 	api.agentProvider = stn
+
+	api.chatDaemon = chatd.New(chatd.Config{
+		Logger:              options.Logger.Named("chats"),
+		Database:            options.Database,
+		ReplicaID:           api.ID,
+		RemotePartsProvider: options.ChatRemotePartsProvider,
+		ProviderAPIKeys:     chatProviderAPIKeysFromDeploymentValues(options.DeploymentValues),
+		AgentConn:           api.agentProvider.AgentConn,
+		CreateWorkspace:     api.chatCreateWorkspace,
+		Pubsub:              options.Pubsub,
+	})
 	if options.DeploymentValues.Prometheus.Enable {
 		options.PrometheusRegistry.MustRegister(stn)
 		api.lifecycleMetrics = agentapi.NewLifecycleMetrics(options.PrometheusRegistry)
@@ -1085,6 +1099,48 @@ func New(options *Options) *API {
 				})
 			})
 		})
+		r.Route("/chats", func(r chi.Router) {
+			r.Use(
+				apiKeyMiddleware,
+				httpmw.RequireExperimentWithDevBypass(api.Experiments, codersdk.ExperimentAgents),
+			)
+			r.Get("/", api.listChats)
+			r.Post("/", api.postChats)
+			r.Get("/models", api.listChatModels)
+			r.Get("/watch", api.watchChats)
+			r.Route("/providers", func(r chi.Router) {
+				r.Get("/", api.listChatProviders)
+				r.Post("/", api.createChatProvider)
+				r.Route("/{providerConfig}", func(r chi.Router) {
+					r.Patch("/", api.updateChatProvider)
+					r.Delete("/", api.deleteChatProvider)
+				})
+			})
+			r.Route("/model-configs", func(r chi.Router) {
+				r.Get("/", api.listChatModelConfigs)
+				r.Post("/", api.createChatModelConfig)
+				r.Route("/{modelConfig}", func(r chi.Router) {
+					r.Patch("/", api.updateChatModelConfig)
+					r.Delete("/", api.deleteChatModelConfig)
+				})
+			})
+			r.Route("/{chat}", func(r chi.Router) {
+				r.Use(httpmw.ExtractChatParam(options.Database))
+				r.Get("/", api.getChat)
+				r.Delete("/", api.deleteChat)
+				r.Post("/messages", api.postChatMessages)
+				r.Patch("/messages/{message}", api.patchChatMessage)
+				r.Get("/stream", api.streamChat)
+				r.Post("/interrupt", api.interruptChat)
+				r.Get("/diff-status", api.getChatDiffStatus)
+				r.Get("/diff", api.getChatDiffContents)
+				r.Route("/queue/{queuedMessage}", func(r chi.Router) {
+					r.Delete("/", api.deleteChatQueuedMessage)
+					r.Post("/promote", api.promoteChatQueuedMessage)
+				})
+			})
+		})
+
 		r.Route("/mcp", func(r chi.Router) {
 			r.Use(
 				apiKeyMiddleware,
@@ -1902,6 +1958,8 @@ type API struct {
 	// dbRolluper rolls up template usage stats from raw agent and app
 	// stats. This is used to provide insights in the WebUI.
 	dbRolluper *dbrollup.Rolluper
+	// chatDaemon handles background processing of pending chats.
+	chatDaemon *chatd.Server
 }
 
 // Close waits for all WebSocket connections to drain before returning.
@@ -1930,8 +1988,10 @@ func (api *API) Close() error {
 	case <-timer.C:
 		api.Logger.Warn(api.ctx, "websocket shutdown timed out after 10 seconds")
 	}
-
 	api.dbRolluper.Close()
+	if err := api.chatDaemon.Close(); err != nil {
+		api.Logger.Warn(api.ctx, "close chat processor", slog.Error(err))
+	}
 	api.metricsCache.Close()
 	if api.updateChecker != nil {
 		api.updateChecker.Close()