feat: add chat read/unread indicator to sidebar (#23129)

## Summary

Adds read/unread tracking for chats so users can see which agent
conversations have new assistant messages they haven't viewed.

## Backend Changes

- Adds `last_read_message_id` column to the `chats` table (migration
000439).
- Computes `has_unread` as a virtual column in `GetChatsByOwnerID` using
an `EXISTS` subquery checking for assistant messages beyond the read
cursor.
- Exposes `has_unread` on the `codersdk.Chat` struct and auto-generated
TypeScript types.
- Updates `last_read_message_id` on stream connect/disconnect in
`streamChat`, avoiding per-message API calls during active streaming.
- Uses `context.WithoutCancel` for the deferred disconnect write so the
DB update succeeds even after the client disconnects.

## Frontend Changes

- Bold title (`font-semibold`) for unread chats in the sidebar.
- Small blue dot indicator next to the relative timestamp.
- Suppresses unread indicator for the currently active chat via
`isActive` from NavLink.

## Design Decisions

- Only `assistant` messages count as unread — the user's own messages
don't trigger the indicator.
- No foreign key on `last_read_message_id` since messages can be deleted
(via rollback/truncation) and the column is just a high-water mark.
- Zero API calls during streaming: exactly 2 DB writes per stream
session (connect + disconnect).
- Unread state refreshes on chat list load and window focus. The
`watchChats` WebSocket optimistically marks non-active chats as unread
on `status_change` events, but does not carry a server-computed
`has_unread` field. Navigating to a chat optimistically clears its
unread indicator in the cache.

coderd/database/queries.sql.go

@@ -4013,7 +4013,7 @@ WHERE
             $3::int
     )
 RETURNING
-    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type AcquireChatsParams struct {
@@ -4055,6 +4055,7 @@ func (q *sqlQuerier) AcquireChats(ctx context.Context, arg AcquireChatsParams) (
 			&i.BuildID,
 			&i.AgentID,
 			&i.PinOrder,
+			&i.LastReadMessageID,
 		); err != nil {
 			return nil, err
 		}
@@ -4288,7 +4289,7 @@ func (q *sqlQuerier) DeleteChatUsageLimitUserOverride(ctx context.Context, userI
 
 const getChatByID = `-- name: GetChatByID :one
 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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 FROM
     chats
 WHERE
@@ -4320,12 +4321,13 @@ func (q *sqlQuerier) GetChatByID(ctx context.Context, id uuid.UUID) (Chat, error
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
 
 const getChatByIDForUpdate = `-- name: GetChatByIDForUpdate :one
-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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order 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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id FROM chats WHERE id = $1::uuid FOR UPDATE
 `
 
 func (q *sqlQuerier) GetChatByIDForUpdate(ctx context.Context, id uuid.UUID) (Chat, error) {
@@ -4353,6 +4355,7 @@ func (q *sqlQuerier) GetChatByIDForUpdate(ctx context.Context, id uuid.UUID) (Ch
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
@@ -5264,7 +5267,14 @@ func (q *sqlQuerier) GetChatUsageLimitUserOverride(ctx context.Context, userID u
 
 const getChats = `-- name: GetChats :many
 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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    chats.id, chats.owner_id, chats.workspace_id, chats.title, chats.status, chats.worker_id, chats.started_at, chats.heartbeat_at, chats.created_at, chats.updated_at, chats.parent_chat_id, chats.root_chat_id, chats.last_model_config_id, chats.archived, chats.last_error, chats.mode, chats.mcp_server_ids, chats.labels, chats.build_id, chats.agent_id, chats.pin_order, chats.last_read_message_id,
+    EXISTS (
+        SELECT 1 FROM chat_messages cm
+        WHERE cm.chat_id = chats.id
+            AND cm.role = 'assistant'
+            AND cm.deleted = false
+            AND cm.id > COALESCE(chats.last_read_message_id, 0)
+    ) AS has_unread
 FROM
     chats
 WHERE
@@ -5320,7 +5330,12 @@ type GetChatsParams struct {
 	LimitOpt    int32                 `db:"limit_opt" json:"limit_opt"`
 }
 
-func (q *sqlQuerier) GetChats(ctx context.Context, arg GetChatsParams) ([]Chat, error) {
+type GetChatsRow struct {
+	Chat      Chat `db:"chat" json:"chat"`
+	HasUnread bool `db:"has_unread" json:"has_unread"`
+}
+
+func (q *sqlQuerier) GetChats(ctx context.Context, arg GetChatsParams) ([]GetChatsRow, error) {
 	rows, err := q.db.QueryContext(ctx, getChats,
 		arg.OwnerID,
 		arg.Archived,
@@ -5333,31 +5348,33 @@ func (q *sqlQuerier) GetChats(ctx context.Context, arg GetChatsParams) ([]Chat,
 		return nil, err
 	}
 	defer rows.Close()
-	var items []Chat
+	var items []GetChatsRow
 	for rows.Next() {
-		var i Chat
+		var i GetChatsRow
 		if err := rows.Scan(
-			&i.ID,
-			&i.OwnerID,
-			&i.WorkspaceID,
-			&i.Title,
-			&i.Status,
-			&i.WorkerID,
-			&i.StartedAt,
-			&i.HeartbeatAt,
-			&i.CreatedAt,
-			&i.UpdatedAt,
-			&i.ParentChatID,
-			&i.RootChatID,
-			&i.LastModelConfigID,
-			&i.Archived,
-			&i.LastError,
-			&i.Mode,
-			pq.Array(&i.MCPServerIDs),
-			&i.Labels,
-			&i.BuildID,
-			&i.AgentID,
-			&i.PinOrder,
+			&i.Chat.ID,
+			&i.Chat.OwnerID,
+			&i.Chat.WorkspaceID,
+			&i.Chat.Title,
+			&i.Chat.Status,
+			&i.Chat.WorkerID,
+			&i.Chat.StartedAt,
+			&i.Chat.HeartbeatAt,
+			&i.Chat.CreatedAt,
+			&i.Chat.UpdatedAt,
+			&i.Chat.ParentChatID,
+			&i.Chat.RootChatID,
+			&i.Chat.LastModelConfigID,
+			&i.Chat.Archived,
+			&i.Chat.LastError,
+			&i.Chat.Mode,
+			pq.Array(&i.Chat.MCPServerIDs),
+			&i.Chat.Labels,
+			&i.Chat.BuildID,
+			&i.Chat.AgentID,
+			&i.Chat.PinOrder,
+			&i.Chat.LastReadMessageID,
+			&i.HasUnread,
 		); err != nil {
 			return nil, err
 		}
@@ -5373,7 +5390,7 @@ func (q *sqlQuerier) GetChats(ctx context.Context, arg GetChatsParams) ([]Chat,
 }
 
 const getChatsByWorkspaceIDs = `-- name: GetChatsByWorkspaceIDs :many
-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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 FROM chats
 WHERE archived = false
   AND workspace_id = ANY($1::uuid[])
@@ -5411,6 +5428,7 @@ func (q *sqlQuerier) GetChatsByWorkspaceIDs(ctx context.Context, ids []uuid.UUID
 			&i.BuildID,
 			&i.AgentID,
 			&i.PinOrder,
+			&i.LastReadMessageID,
 		); err != nil {
 			return nil, err
 		}
@@ -5476,7 +5494,7 @@ func (q *sqlQuerier) GetLastChatMessageByRole(ctx context.Context, arg GetLastCh
 
 const getStaleChats = `-- name: GetStaleChats :many
 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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 FROM
     chats
 WHERE
@@ -5517,6 +5535,7 @@ func (q *sqlQuerier) GetStaleChats(ctx context.Context, staleThreshold time.Time
 			&i.BuildID,
 			&i.AgentID,
 			&i.PinOrder,
+			&i.LastReadMessageID,
 		); err != nil {
 			return nil, err
 		}
@@ -5598,7 +5617,7 @@ INSERT INTO chats (
     COALESCE($11::jsonb, '{}'::jsonb)
 )
 RETURNING
-    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type InsertChatParams struct {
@@ -5652,6 +5671,7 @@ func (q *sqlQuerier) InsertChat(ctx context.Context, arg InsertChatParams) (Chat
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
@@ -6165,7 +6185,7 @@ UPDATE chats SET
     updated_at = NOW()
 WHERE
     id = $3::uuid
-RETURNING 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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+RETURNING 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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type UpdateChatBuildAgentBindingParams struct {
@@ -6199,6 +6219,7 @@ func (q *sqlQuerier) UpdateChatBuildAgentBinding(ctx context.Context, arg Update
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
@@ -6212,7 +6233,7 @@ SET
 WHERE
     id = $2::uuid
 RETURNING
-    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type UpdateChatByIDParams struct {
@@ -6245,6 +6266,7 @@ func (q *sqlQuerier) UpdateChatByID(ctx context.Context, arg UpdateChatByIDParam
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
@@ -6284,7 +6306,7 @@ SET
 WHERE
     id = $2::uuid
 RETURNING
-    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type UpdateChatLabelsByIDParams struct {
@@ -6317,6 +6339,7 @@ func (q *sqlQuerier) UpdateChatLabelsByID(ctx context.Context, arg UpdateChatLab
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
@@ -6330,7 +6353,7 @@ SET
 WHERE
     id = $2::uuid
 RETURNING
-    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type UpdateChatLastModelConfigByIDParams struct {
@@ -6363,10 +6386,29 @@ func (q *sqlQuerier) UpdateChatLastModelConfigByID(ctx context.Context, arg Upda
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
 
+const updateChatLastReadMessageID = `-- name: UpdateChatLastReadMessageID :exec
+UPDATE chats
+SET last_read_message_id = $1::bigint
+WHERE id = $2::uuid
+`
+
+type UpdateChatLastReadMessageIDParams struct {
+	LastReadMessageID int64     `db:"last_read_message_id" json:"last_read_message_id"`
+	ID                uuid.UUID `db:"id" json:"id"`
+}
+
+// Updates the last read message ID for a chat. This is used to track
+// which messages the owner has seen, enabling unread indicators.
+func (q *sqlQuerier) UpdateChatLastReadMessageID(ctx context.Context, arg UpdateChatLastReadMessageIDParams) error {
+	_, err := q.db.ExecContext(ctx, updateChatLastReadMessageID, arg.LastReadMessageID, arg.ID)
+	return err
+}
+
 const updateChatMCPServerIDs = `-- name: UpdateChatMCPServerIDs :one
 UPDATE
     chats
@@ -6376,7 +6418,7 @@ SET
 WHERE
     id = $2::uuid
 RETURNING
-    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type UpdateChatMCPServerIDsParams struct {
@@ -6409,6 +6451,7 @@ func (q *sqlQuerier) UpdateChatMCPServerIDs(ctx context.Context, arg UpdateChatM
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
@@ -6544,7 +6587,7 @@ SET
 WHERE
     id = $6::uuid
 RETURNING
-    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type UpdateChatStatusParams struct {
@@ -6588,6 +6631,7 @@ func (q *sqlQuerier) UpdateChatStatus(ctx context.Context, arg UpdateChatStatusP
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
@@ -6605,7 +6649,7 @@ SET
 WHERE
     id = $7::uuid
 RETURNING
-    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+    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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type UpdateChatStatusPreserveUpdatedAtParams struct {
@@ -6651,6 +6695,7 @@ func (q *sqlQuerier) UpdateChatStatusPreserveUpdatedAt(ctx context.Context, arg
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }
@@ -6662,7 +6707,7 @@ UPDATE chats SET
     agent_id = $3::uuid,
     updated_at = NOW()
 WHERE id = $4::uuid
-RETURNING 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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order
+RETURNING 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, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
 `
 
 type UpdateChatWorkspaceBindingParams struct {
@@ -6702,6 +6747,7 @@ func (q *sqlQuerier) UpdateChatWorkspaceBinding(ctx context.Context, arg UpdateC
 		&i.BuildID,
 		&i.AgentID,
 		&i.PinOrder,
+		&i.LastReadMessageID,
 	)
 	return i, err
 }