chore(db): remove workspace_agent_id from chats table (#22442)

## Summary

Remove the `workspace_agent_id` column from the `chats` table and
dynamically look up the first workspace agent instead.

## Problem

When a workspace is stopped and restarted, the workspace agent gets a
new ID. The `workspace_agent_id` stored on the chat at creation time
becomes stale, making the agent unreachable. This caused chats to break
after workspace restarts.

## Solution

Instead of persisting the agent ID, dynamically look up the first agent
from the workspace's latest build via
`GetWorkspaceAgentsInLatestBuildByWorkspaceID` whenever an agent
connection is needed. The `workspace_id` on the chat remains stable
across restarts.

This behavior may be refined later (e.g., agent selection heuristics),
but picking the first agent resolves the immediate breakage.

## Changes

- **Migration 000425**: Drop `workspace_agent_id` column from `chats`
- **SQL queries**: Remove `workspace_agent_id` from `InsertChat` and
`UpdateChatWorkspace`
- **chatd.go**: `getWorkspaceConn` and `resolveInstructions` now look up
agents dynamically from workspace ID
- **chatd.go**: Remove `refreshChatWorkspaceSnapshot` (no longer needed)
- **createworkspace.go**: Stop persisting agent ID when associating
workspace with chat
- **subagent.go**: Stop passing agent ID to child chats
- **SDK/frontend**: Remove `WorkspaceAgentID` / `workspace_agent_id`
from Chat type

---------

Co-authored-by: Kyle Carberry <kylecarbs@gmail.com>

coderd/chatd/chatd.go

@@ -133,7 +133,6 @@ var (
 type CreateOptions struct {
 	OwnerID            uuid.UUID
 	WorkspaceID        uuid.NullUUID
-	WorkspaceAgentID   uuid.NullUUID
 	ParentChatID       uuid.NullUUID
 	RootChatID         uuid.NullUUID
 	Title              string
@@ -212,7 +211,6 @@ func (p *Server) CreateChat(ctx context.Context, opts CreateOptions) (database.C
 		insertedChat, err := tx.InsertChat(ctx, database.InsertChatParams{
 			OwnerID:           opts.OwnerID,
 			WorkspaceID:       opts.WorkspaceID,
-			WorkspaceAgentID:  opts.WorkspaceAgentID,
 			ParentChatID:      opts.ParentChatID,
 			RootChatID:        opts.RootChatID,
 			LastModelConfigID: opts.ModelConfigID,
@@ -1421,10 +1419,6 @@ func (p *Server) publishChatPubsubEvent(chat database.Chat, kind coderdpubsub.Ch
 	if chat.WorkspaceID.Valid {
 		sdkChat.WorkspaceID = &chat.WorkspaceID.UUID
 	}
-	if chat.WorkspaceAgentID.Valid {
-		sdkChat.WorkspaceAgentID = &chat.WorkspaceAgentID.UUID
-	}
-
 	event := coderdpubsub.ChatEvent{
 		Kind: kind,
 		Chat: sdkChat,
@@ -1825,13 +1819,6 @@ func (p *Server) runChat(
 	}()
 
 	currentChat := chat
-	loadChatSnapshot := func(
-		loadCtx context.Context,
-		chatID uuid.UUID,
-	) (database.Chat, error) {
-		//nolint:gocritic // System context required to load chat snapshots for the stream.
-		return p.db.GetChatByID(dbauthz.AsSystemRestricted(loadCtx), chatID)
-	}
 	var (
 		chatStateMu sync.Mutex
 		workspaceMu sync.Mutex
@@ -1860,28 +1847,20 @@ func (p *Server) runChat(
 			return nil, xerrors.New("workspace agent connector is not configured")
 		}
 
-		if !chatSnapshot.WorkspaceAgentID.Valid {
-			refreshedChat, refreshErr := refreshChatWorkspaceSnapshot(
-				ctx,
-				chatSnapshot,
-				loadChatSnapshot,
-			)
-			if refreshErr != nil {
-				return nil, refreshErr
-			}
-			if refreshedChat.WorkspaceAgentID.Valid {
-				chatStateMu.Lock()
-				currentChat = refreshedChat
-				chatSnapshot = refreshedChat
-				chatStateMu.Unlock()
-			}
+		if !chatSnapshot.WorkspaceID.Valid {
+			return nil, xerrors.New("chat has no workspace")
 		}
 
-		if !chatSnapshot.WorkspaceAgentID.Valid {
+		//nolint:gocritic // System context needed to look up workspace agents.
+		agents, err := p.db.GetWorkspaceAgentsInLatestBuildByWorkspaceID(
+			dbauthz.AsSystemRestricted(ctx),
+			chatSnapshot.WorkspaceID.UUID,
+		)
+		if err != nil || len(agents) == 0 {
 			return nil, xerrors.New("chat has no workspace agent")
 		}
 
-		agentConn, agentRelease, err := p.agentConnFn(ctx, chatSnapshot.WorkspaceAgentID.UUID)
+		agentConn, agentRelease, err := p.agentConnFn(ctx, agents[0].ID)
 		if err != nil {
 			return nil, xerrors.Errorf("connect to workspace agent: %w", err)
 		}
@@ -2376,23 +2355,6 @@ func usageNullInt64(value int64, valid bool) sql.NullInt64 {
 	}
 }
 
-func refreshChatWorkspaceSnapshot(
-	ctx context.Context,
-	chat database.Chat,
-	loadChat func(context.Context, uuid.UUID) (database.Chat, error),
-) (database.Chat, error) {
-	if chat.WorkspaceAgentID.Valid || loadChat == nil {
-		return chat, nil
-	}
-
-	refreshedChat, err := loadChat(ctx, chat.ID)
-	if err != nil {
-		return chat, xerrors.Errorf("reload chat workspace state: %w", err)
-	}
-
-	return refreshedChat, nil
-}
-
 // resolveInstructions returns the combined system instructions for the
 // workspace agent. It reads the home-level (~/.coder/AGENTS.md) and
 // working-directory-level (<pwd>/AGENTS.md) instruction files, combines
@@ -2402,10 +2364,19 @@ func (p *Server) resolveInstructions(
 	chat database.Chat,
 	getWorkspaceConn func(context.Context) (workspacesdk.AgentConn, error),
 ) string {
-	if !chat.WorkspaceAgentID.Valid {
+	if !chat.WorkspaceID.Valid {
 		return ""
 	}
-	agentID := chat.WorkspaceAgentID.UUID
+
+	//nolint:gocritic // System context needed to look up workspace agents.
+	agents, agentsErr := p.db.GetWorkspaceAgentsInLatestBuildByWorkspaceID(
+		dbauthz.AsSystemRestricted(ctx),
+		chat.WorkspaceID.UUID,
+	)
+	if agentsErr != nil || len(agents) == 0 {
+		return ""
+	}
+	agentID := agents[0].ID
 
 	p.instructionCacheMu.Lock()
 	cached, ok := p.instructionCache[agentID]

coderd/chatd/chattool/createworkspace.go

@@ -191,10 +191,6 @@ func CreateWorkspace(options CreateWorkspaceOptions) fantasy.AgentTool {
 						UUID:  workspace.ID,
 						Valid: true,
 					},
-					WorkspaceAgentID: uuid.NullUUID{
-						UUID:  workspaceAgentID,
-						Valid: workspaceAgentID != uuid.Nil,
-					},
 				})
 			}
 
@@ -281,14 +277,15 @@ func checkExistingWorkspace(
 
 	case database.ProvisionerJobStatusSucceeded:
 		// Build succeeded — check if agent is reachable.
-		if chat.WorkspaceAgentID.Valid && agentConnFn != nil {
+		agents, agentsErr := db.GetWorkspaceAgentsInLatestBuildByWorkspaceID(ctx, ws.ID)
+		if agentsErr == nil && len(agents) > 0 && agentConnFn != nil {
 			pingCtx, cancel := context.WithTimeout(
 				ctx, agentPingTimeout,
 			)
 			defer cancel()
 
 			conn, release, connErr := agentConnFn(
-				pingCtx, chat.WorkspaceAgentID.UUID,
+				pingCtx, agents[0].ID,
 			)
 			if connErr == nil {
 				release()

coderd/chatd/subagent.go

@@ -240,9 +240,8 @@ func (p *Server) createChildSubagentChat(
 	}
 
 	child, err := p.CreateChat(ctx, CreateOptions{
-		OwnerID:          parent.OwnerID,
-		WorkspaceID:      parent.WorkspaceID,
-		WorkspaceAgentID: parent.WorkspaceAgentID,
+		OwnerID:     parent.OwnerID,
+		WorkspaceID: parent.WorkspaceID,
 		ParentChatID: uuid.NullUUID{
 			UUID:  parent.ID,
 			Valid: true,

coderd/chats.go

@@ -258,7 +258,6 @@ func (api *API) postChats(rw http.ResponseWriter, r *http.Request) {
 	chat, err := api.chatDaemon.CreateChat(ctx, chatd.CreateOptions{
 		OwnerID:            apiKey.UserID,
 		WorkspaceID:        workspaceSelection.WorkspaceID,
-		WorkspaceAgentID:   workspaceSelection.WorkspaceAgentID,
 		Title:              title,
 		ModelConfigID:      modelConfigID,
 		SystemPrompt:       defaultChatSystemPrompt(),
@@ -1854,8 +1853,7 @@ func parseGitHubPullRequestURL(raw string) (githubPullRequestRef, bool) {
 }
 
 type createChatWorkspaceSelection struct {
-	WorkspaceID      uuid.NullUUID
-	WorkspaceAgentID uuid.NullUUID
+	WorkspaceID uuid.NullUUID
 }
 
 func (api *API) validateCreateChatWorkspaceSelection(
@@ -1888,23 +1886,6 @@ func (api *API) validateCreateChatWorkspaceSelection(
 		Valid: true,
 	}
 
-	workspaceAgents, err := api.Database.GetWorkspaceAgentsInLatestBuildByWorkspaceID(
-		ctx,
-		workspace.ID,
-	)
-	if err != nil {
-		return selection, http.StatusInternalServerError, &codersdk.Response{
-			Message: "Failed to get workspace agents.",
-			Detail:  err.Error(),
-		}
-	}
-	if len(workspaceAgents) > 0 {
-		selection.WorkspaceAgentID = uuid.NullUUID{
-			UUID:  workspaceAgents[0].ID,
-			Valid: true,
-		}
-	}
-
 	return selection, 0, nil
 }
 
@@ -2081,9 +2062,6 @@ func convertChat(c database.Chat, diffStatus *database.ChatDiffStatus) codersdk.
 	if c.WorkspaceID.Valid {
 		chat.WorkspaceID = &c.WorkspaceID.UUID
 	}
-	if c.WorkspaceAgentID.Valid {
-		chat.WorkspaceAgentID = &c.WorkspaceAgentID.UUID
-	}
 	if diffStatus != nil {
 		convertedDiffStatus := convertChatDiffStatus(c.ID, diffStatus)
 		chat.DiffStatus = &convertedDiffStatus

coderd/chats_test.go

@@ -77,7 +77,6 @@ func TestPostChats(t *testing.T) {
 		require.NotZero(t, chat.CreatedAt)
 		require.NotZero(t, chat.UpdatedAt)
 		require.Nil(t, chat.WorkspaceID)
-		require.Nil(t, chat.WorkspaceAgentID)
 		require.NotNil(t, chat.RootChatID)
 		require.Equal(t, chat.ID, *chat.RootChatID)
 
@@ -206,8 +205,6 @@ func TestPostChats(t *testing.T) {
 		require.NoError(t, err)
 		require.NotNil(t, chat.WorkspaceID)
 		require.Equal(t, workspaceBuild.Workspace.ID, *chat.WorkspaceID)
-		require.NotNil(t, chat.WorkspaceAgentID)
-		require.Equal(t, workspaceBuild.Agents[0].ID, *chat.WorkspaceAgentID)
 		require.Equal(t, modelConfig.ID, chat.LastModelConfigID)
 	})
 
@@ -342,7 +339,6 @@ func TestListChats(t *testing.T) {
 			require.NotZero(t, chat.UpdatedAt)
 			require.Nil(t, chat.ParentChatID)
 			require.Nil(t, chat.WorkspaceID)
-			require.Nil(t, chat.WorkspaceAgentID)
 			require.NotNil(t, chat.RootChatID)
 			require.Equal(t, chat.ID, *chat.RootChatID)
 			require.NotNil(t, chat.DiffStatus)

coderd/database/dbauthz/dbauthz_test.go

@@ -694,9 +694,8 @@ func (s *MethodTestSuite) TestChats() {
 	s.Run("UpdateChatWorkspace", s.Mocked(func(dbm *dbmock.MockStore, faker *gofakeit.Faker, check *expects) {
 		chat := testutil.Fake(s.T(), faker, database.Chat{})
 		arg := database.UpdateChatWorkspaceParams{
-			ID:               chat.ID,
-			WorkspaceID:      uuid.NullUUID{UUID: uuid.New(), Valid: true},
-			WorkspaceAgentID: uuid.NullUUID{UUID: uuid.New(), Valid: true},
+			ID:          chat.ID,
+			WorkspaceID: uuid.NullUUID{UUID: uuid.New(), Valid: true},
 		}
 		updatedChat := testutil.Fake(s.T(), faker, database.Chat{ID: chat.ID})
 		dbm.EXPECT().GetChatByID(gomock.Any(), chat.ID).Return(chat, nil).AnyTimes()

coderd/database/dump.sql

@@ -1263,7 +1263,6 @@ CREATE TABLE chats (
     id uuid DEFAULT gen_random_uuid() NOT NULL,
     owner_id uuid NOT NULL,
     workspace_id uuid,
-    workspace_agent_id uuid,
     title text DEFAULT 'New Chat'::text NOT NULL,
     status chat_status DEFAULT 'waiting'::chat_status NOT NULL,
     worker_id uuid,
@@ -3790,9 +3789,6 @@ ALTER TABLE ONLY chats
 ALTER TABLE ONLY chats
     ADD CONSTRAINT chats_root_chat_id_fkey FOREIGN KEY (root_chat_id) REFERENCES chats(id) ON DELETE SET NULL;
 
-ALTER TABLE ONLY chats
-    ADD CONSTRAINT chats_workspace_agent_id_fkey FOREIGN KEY (workspace_agent_id) REFERENCES workspace_agents(id) ON DELETE SET NULL;
-
 ALTER TABLE ONLY chats
     ADD CONSTRAINT chats_workspace_id_fkey FOREIGN KEY (workspace_id) REFERENCES workspaces(id) ON DELETE SET NULL;
 

coderd/database/foreign_key_constraint.go

@@ -21,7 +21,6 @@ const (
 	ForeignKeyChatsOwnerID                                        ForeignKeyConstraint = "chats_owner_id_fkey"                                             // ALTER TABLE ONLY chats ADD CONSTRAINT chats_owner_id_fkey FOREIGN KEY (owner_id) REFERENCES users(id) ON DELETE CASCADE;
 	ForeignKeyChatsParentChatID                                   ForeignKeyConstraint = "chats_parent_chat_id_fkey"                                       // ALTER TABLE ONLY chats ADD CONSTRAINT chats_parent_chat_id_fkey FOREIGN KEY (parent_chat_id) REFERENCES chats(id) ON DELETE SET NULL;
 	ForeignKeyChatsRootChatID                                     ForeignKeyConstraint = "chats_root_chat_id_fkey"                                         // ALTER TABLE ONLY chats ADD CONSTRAINT chats_root_chat_id_fkey FOREIGN KEY (root_chat_id) REFERENCES chats(id) ON DELETE SET NULL;
-	ForeignKeyChatsWorkspaceAgentID                               ForeignKeyConstraint = "chats_workspace_agent_id_fkey"                                   // ALTER TABLE ONLY chats ADD CONSTRAINT chats_workspace_agent_id_fkey FOREIGN KEY (workspace_agent_id) REFERENCES workspace_agents(id) ON DELETE SET NULL;
 	ForeignKeyChatsWorkspaceID                                    ForeignKeyConstraint = "chats_workspace_id_fkey"                                         // ALTER TABLE ONLY chats ADD CONSTRAINT chats_workspace_id_fkey FOREIGN KEY (workspace_id) REFERENCES workspaces(id) ON DELETE SET NULL;
 	ForeignKeyConnectionLogsOrganizationID                        ForeignKeyConstraint = "connection_logs_organization_id_fkey"                            // ALTER TABLE ONLY connection_logs ADD CONSTRAINT connection_logs_organization_id_fkey FOREIGN KEY (organization_id) REFERENCES organizations(id) ON DELETE CASCADE;
 	ForeignKeyConnectionLogsWorkspaceID                           ForeignKeyConstraint = "connection_logs_workspace_id_fkey"                               // ALTER TABLE ONLY connection_logs ADD CONSTRAINT connection_logs_workspace_id_fkey FOREIGN KEY (workspace_id) REFERENCES workspaces(id) ON DELETE CASCADE;

coderd/database/migrations/000425_remove_chat_workspace_agent_id.down.sql

@@ -0,0 +1 @@
+ALTER TABLE chats ADD COLUMN workspace_agent_id UUID REFERENCES workspace_agents(id) ON DELETE SET NULL;

coderd/database/migrations/000425_remove_chat_workspace_agent_id.up.sql

@@ -0,0 +1 @@
+ALTER TABLE chats DROP COLUMN workspace_agent_id;

coderd/database/models.go

@@ -3889,7 +3889,6 @@ type Chat struct {
 	ID                uuid.UUID      `db:"id" json:"id"`
 	OwnerID           uuid.UUID      `db:"owner_id" json:"owner_id"`
 	WorkspaceID       uuid.NullUUID  `db:"workspace_id" json:"workspace_id"`
-	WorkspaceAgentID  uuid.NullUUID  `db:"workspace_agent_id" json:"workspace_agent_id"`
 	Title             string         `db:"title" json:"title"`
 	Status            ChatStatus     `db:"status" json:"status"`
 	WorkerID          uuid.NullUUID  `db:"worker_id" json:"worker_id"`

coderd/database/queries.sql.go

@@ -2842,7 +2842,7 @@ WHERE
             1
     )
 RETURNING
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 `
 
 type AcquireChatParams struct {
@@ -2859,7 +2859,6 @@ func (q *sqlQuerier) AcquireChat(ctx context.Context, arg AcquireChatParams) (Ch
 		&i.ID,
 		&i.OwnerID,
 		&i.WorkspaceID,
-		&i.WorkspaceAgentID,
 		&i.Title,
 		&i.Status,
 		&i.WorkerID,
@@ -2940,7 +2939,7 @@ func (q *sqlQuerier) DeleteChatQueuedMessage(ctx context.Context, arg DeleteChat
 
 const getChatByID = `-- name: GetChatByID :one
 SELECT
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 FROM
     chats
 WHERE
@@ -2954,7 +2953,6 @@ func (q *sqlQuerier) GetChatByID(ctx context.Context, id uuid.UUID) (Chat, error
 		&i.ID,
 		&i.OwnerID,
 		&i.WorkspaceID,
-		&i.WorkspaceAgentID,
 		&i.Title,
 		&i.Status,
 		&i.WorkerID,
@@ -2972,7 +2970,7 @@ func (q *sqlQuerier) GetChatByID(ctx context.Context, id uuid.UUID) (Chat, error
 }
 
 const getChatByIDForUpdate = `-- name: GetChatByIDForUpdate :one
-SELECT id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error FROM chats WHERE id = $1::uuid FOR UPDATE
+SELECT id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error FROM chats WHERE id = $1::uuid FOR UPDATE
 `
 
 func (q *sqlQuerier) GetChatByIDForUpdate(ctx context.Context, id uuid.UUID) (Chat, error) {
@@ -2982,7 +2980,6 @@ func (q *sqlQuerier) GetChatByIDForUpdate(ctx context.Context, id uuid.UUID) (Ch
 		&i.ID,
 		&i.OwnerID,
 		&i.WorkspaceID,
-		&i.WorkspaceAgentID,
 		&i.Title,
 		&i.Status,
 		&i.WorkerID,
@@ -3291,7 +3288,7 @@ func (q *sqlQuerier) GetChatQueuedMessages(ctx context.Context, chatID uuid.UUID
 
 const getChatsByOwnerID = `-- name: GetChatsByOwnerID :many
 SELECT
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 FROM
     chats
 WHERE
@@ -3314,7 +3311,6 @@ func (q *sqlQuerier) GetChatsByOwnerID(ctx context.Context, ownerID uuid.UUID) (
 			&i.ID,
 			&i.OwnerID,
 			&i.WorkspaceID,
-			&i.WorkspaceAgentID,
 			&i.Title,
 			&i.Status,
 			&i.WorkerID,
@@ -3343,7 +3339,7 @@ func (q *sqlQuerier) GetChatsByOwnerID(ctx context.Context, ownerID uuid.UUID) (
 
 const getStaleChats = `-- name: GetStaleChats :many
 SELECT
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 FROM
     chats
 WHERE
@@ -3366,7 +3362,6 @@ func (q *sqlQuerier) GetStaleChats(ctx context.Context, staleThreshold time.Time
 			&i.ID,
 			&i.OwnerID,
 			&i.WorkspaceID,
-			&i.WorkspaceAgentID,
 			&i.Title,
 			&i.Status,
 			&i.WorkerID,
@@ -3397,7 +3392,6 @@ const insertChat = `-- name: InsertChat :one
 INSERT INTO chats (
     owner_id,
     workspace_id,
-    workspace_agent_id,
     parent_chat_id,
     root_chat_id,
     last_model_config_id,
@@ -3408,17 +3402,15 @@ INSERT INTO chats (
     $3::uuid,
     $4::uuid,
     $5::uuid,
-    $6::uuid,
-    $7::text
+    $6::text
 )
 RETURNING
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 `
 
 type InsertChatParams struct {
 	OwnerID           uuid.UUID     `db:"owner_id" json:"owner_id"`
 	WorkspaceID       uuid.NullUUID `db:"workspace_id" json:"workspace_id"`
-	WorkspaceAgentID  uuid.NullUUID `db:"workspace_agent_id" json:"workspace_agent_id"`
 	ParentChatID      uuid.NullUUID `db:"parent_chat_id" json:"parent_chat_id"`
 	RootChatID        uuid.NullUUID `db:"root_chat_id" json:"root_chat_id"`
 	LastModelConfigID uuid.UUID     `db:"last_model_config_id" json:"last_model_config_id"`
@@ -3429,7 +3421,6 @@ func (q *sqlQuerier) InsertChat(ctx context.Context, arg InsertChatParams) (Chat
 	row := q.db.QueryRowContext(ctx, insertChat,
 		arg.OwnerID,
 		arg.WorkspaceID,
-		arg.WorkspaceAgentID,
 		arg.ParentChatID,
 		arg.RootChatID,
 		arg.LastModelConfigID,
@@ -3440,7 +3431,6 @@ func (q *sqlQuerier) InsertChat(ctx context.Context, arg InsertChatParams) (Chat
 		&i.ID,
 		&i.OwnerID,
 		&i.WorkspaceID,
-		&i.WorkspaceAgentID,
 		&i.Title,
 		&i.Status,
 		&i.WorkerID,
@@ -3578,7 +3568,7 @@ func (q *sqlQuerier) InsertChatQueuedMessage(ctx context.Context, arg InsertChat
 
 const listChatsByRootID = `-- name: ListChatsByRootID :many
 SELECT
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 FROM
     chats
 WHERE
@@ -3600,7 +3590,6 @@ func (q *sqlQuerier) ListChatsByRootID(ctx context.Context, rootChatID uuid.UUID
 			&i.ID,
 			&i.OwnerID,
 			&i.WorkspaceID,
-			&i.WorkspaceAgentID,
 			&i.Title,
 			&i.Status,
 			&i.WorkerID,
@@ -3629,7 +3618,7 @@ func (q *sqlQuerier) ListChatsByRootID(ctx context.Context, rootChatID uuid.UUID
 
 const listChildChatsByParentID = `-- name: ListChildChatsByParentID :many
 SELECT
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 FROM
     chats
 WHERE
@@ -3651,7 +3640,6 @@ func (q *sqlQuerier) ListChildChatsByParentID(ctx context.Context, parentChatID
 			&i.ID,
 			&i.OwnerID,
 			&i.WorkspaceID,
-			&i.WorkspaceAgentID,
 			&i.Title,
 			&i.Status,
 			&i.WorkerID,
@@ -3719,7 +3707,7 @@ SET
 WHERE
     id = $2::uuid
 RETURNING
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 `
 
 type UpdateChatByIDParams struct {
@@ -3734,7 +3722,6 @@ func (q *sqlQuerier) UpdateChatByID(ctx context.Context, arg UpdateChatByIDParam
 		&i.ID,
 		&i.OwnerID,
 		&i.WorkspaceID,
-		&i.WorkspaceAgentID,
 		&i.Title,
 		&i.Status,
 		&i.WorkerID,
@@ -3831,7 +3818,7 @@ SET
 WHERE
     id = $6::uuid
 RETURNING
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 `
 
 type UpdateChatStatusParams struct {
@@ -3857,7 +3844,6 @@ func (q *sqlQuerier) UpdateChatStatus(ctx context.Context, arg UpdateChatStatusP
 		&i.ID,
 		&i.OwnerID,
 		&i.WorkspaceID,
-		&i.WorkspaceAgentID,
 		&i.Title,
 		&i.Status,
 		&i.WorkerID,
@@ -3879,28 +3865,25 @@ UPDATE
     chats
 SET
     workspace_id = $1::uuid,
-    workspace_agent_id = $2::uuid,
     updated_at = NOW()
 WHERE
-    id = $3::uuid
+    id = $2::uuid
 RETURNING
-    id, owner_id, workspace_id, workspace_agent_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error
 `
 
 type UpdateChatWorkspaceParams struct {
-	WorkspaceID      uuid.NullUUID `db:"workspace_id" json:"workspace_id"`
-	WorkspaceAgentID uuid.NullUUID `db:"workspace_agent_id" json:"workspace_agent_id"`
-	ID               uuid.UUID     `db:"id" json:"id"`
+	WorkspaceID uuid.NullUUID `db:"workspace_id" json:"workspace_id"`
+	ID          uuid.UUID     `db:"id" json:"id"`
 }
 
 func (q *sqlQuerier) UpdateChatWorkspace(ctx context.Context, arg UpdateChatWorkspaceParams) (Chat, error) {
-	row := q.db.QueryRowContext(ctx, updateChatWorkspace, arg.WorkspaceID, arg.WorkspaceAgentID, arg.ID)
+	row := q.db.QueryRowContext(ctx, updateChatWorkspace, arg.WorkspaceID, arg.ID)
 	var i Chat
 	err := row.Scan(
 		&i.ID,
 		&i.OwnerID,
 		&i.WorkspaceID,
-		&i.WorkspaceAgentID,
 		&i.Title,
 		&i.Status,
 		&i.WorkerID,

coderd/database/queries/chats.sql

@@ -136,7 +136,6 @@ ORDER BY
 INSERT INTO chats (
     owner_id,
     workspace_id,
-    workspace_agent_id,
     parent_chat_id,
     root_chat_id,
     last_model_config_id,
@@ -144,7 +143,6 @@ INSERT INTO chats (
 ) VALUES (
     @owner_id::uuid,
     sqlc.narg('workspace_id')::uuid,
-    sqlc.narg('workspace_agent_id')::uuid,
     sqlc.narg('parent_chat_id')::uuid,
     sqlc.narg('root_chat_id')::uuid,
     @last_model_config_id::uuid,
@@ -222,7 +220,6 @@ UPDATE
     chats
 SET
     workspace_id = sqlc.narg('workspace_id')::uuid,
-    workspace_agent_id = sqlc.narg('workspace_agent_id')::uuid,
     updated_at = NOW()
 WHERE
     id = @id::uuid

coderd/httpmw/chatparam_test.go

@@ -64,7 +64,6 @@ func TestChatParam(t *testing.T) {
 		chat, err := db.InsertChat(context.Background(), database.InsertChatParams{
 			OwnerID:           ownerID,
 			WorkspaceID:       uuid.NullUUID{},
-			WorkspaceAgentID:  uuid.NullUUID{},
 			ParentChatID:      uuid.NullUUID{},
 			RootChatID:        uuid.NullUUID{},
 			LastModelConfigID: modelConfig.ID,

codersdk/chats.go

@@ -32,7 +32,6 @@ type Chat struct {
 	ID                uuid.UUID       `json:"id" format:"uuid"`
 	OwnerID           uuid.UUID       `json:"owner_id" format:"uuid"`
 	WorkspaceID       *uuid.UUID      `json:"workspace_id,omitempty" format:"uuid"`
-	WorkspaceAgentID  *uuid.UUID      `json:"workspace_agent_id,omitempty" format:"uuid"`
 	ParentChatID      *uuid.UUID      `json:"parent_chat_id,omitempty" format:"uuid"`
 	RootChatID        *uuid.UUID      `json:"root_chat_id,omitempty" format:"uuid"`
 	LastModelConfigID uuid.UUID       `json:"last_model_config_id" format:"uuid"`

site/src/api/typesGenerated.ts

@@ -1054,7 +1054,6 @@ export interface Chat {
 	readonly id: string;
 	readonly owner_id: string;
 	readonly workspace_id?: string;
-	readonly workspace_agent_id?: string;
 	readonly parent_chat_id?: string;
 	readonly root_chat_id?: string;
 	readonly last_model_config_id: string;

site/src/pages/AgentsPage/AgentDetail.stories.tsx

@@ -117,7 +117,6 @@ const mockModelCatalog: TypesGen.ChatModelsResponse = {
 const baseChatFields = {
 	owner_id: "owner-id",
 	workspace_id: mockWorkspace.id,
-	workspace_agent_id: mockWorkspaceAgent.id,
 	last_model_config_id: "model-config-1",
 	created_at: "2026-02-18T00:00:00.000Z",
 	updated_at: "2026-02-18T00:00:00.000Z",

site/src/pages/AgentsPage/AgentDetail.tsx

@@ -494,7 +494,6 @@ const AgentDetail: FC = () => {
 	});
 	const chatsQuery = useQuery(chats());
 	const workspaceId = chatQuery.data?.chat?.workspace_id;
-	const workspaceAgentId = chatQuery.data?.chat?.workspace_agent_id;
 	const workspaceQuery = useQuery({
 		...workspaceById(workspaceId ?? ""),
 		enabled: Boolean(workspaceId),
@@ -507,7 +506,7 @@ const AgentDetail: FC = () => {
 	const chatModelConfigsQuery = useQuery(chatModelConfigs());
 	const hasDiffStatus = Boolean(diffStatusQuery.data?.url);
 	const workspace = workspaceQuery.data;
-	const workspaceAgent = getWorkspaceAgent(workspace, workspaceAgentId);
+	const workspaceAgent = getWorkspaceAgent(workspace, undefined);
 	const chatData = chatQuery.data;
 	const chatRecord = chatData?.chat;
 	const chatMessages = chatData?.messages;