feat: add workspace awareness system message on chat creation (#23213)

When a chat is created via `chatd`, a system message is now inserted
informing the model whether the chat was created with or without a
workspace.

**With workspace:**
> This chat is attached to a workspace. You can use workspace tools like
execute, read_file, write_file, etc.

**Without workspace:**
> There is no workspace associated with this chat yet. Create one using
the create_workspace tool before using workspace tools like execute,
read_file, write_file, etc.

This is a model-only visibility system message (not shown to users) that
helps the model understand its available capabilities upfront —
particularly important for subagents spawned without a workspace, which
previously would attempt to use workspace tools and fail.

**Changes:**
- `coderd/chatd/chatd.go`: Added workspace awareness constants and
inserted the system message in `CreateChat` after the system prompt,
before the initial user message.
- `coderd/chatd/chatd_test.go`: Added
`TestCreateChatInsertsWorkspaceAwarenessMessage` with sub-tests for both
with-workspace and without-workspace cases.

coderd/chatd/chatd.go

@@ -492,6 +492,43 @@ func (p *Server) CreateChat(ctx context.Context, opts CreateOptions) (database.C
 			}
 		}
 
+		var workspaceAwareness string
+		if opts.WorkspaceID.Valid {
+			workspaceAwareness = "This chat is attached to a workspace. You can use workspace tools like execute, read_file, write_file, etc."
+		} else {
+			workspaceAwareness = "There is no workspace associated with this chat yet. Create one using the create_workspace tool before using workspace tools like execute, read_file, write_file, etc."
+		}
+		workspaceAwarenessContent, err := chatprompt.MarshalParts([]codersdk.ChatMessagePart{
+			codersdk.ChatMessageText(workspaceAwareness),
+		})
+		if err != nil {
+			return xerrors.Errorf("marshal workspace awareness: %w", err)
+		}
+		_, err = tx.InsertChatMessage(ctx, database.InsertChatMessageParams{
+			ChatID:    insertedChat.ID,
+			CreatedBy: uuid.NullUUID{},
+			ModelConfigID: uuid.NullUUID{
+				UUID:  opts.ModelConfigID,
+				Valid: true,
+			},
+			Role:                database.ChatMessageRoleSystem,
+			ContentVersion:      chatprompt.CurrentContentVersion,
+			Content:             workspaceAwarenessContent,
+			Visibility:          database.ChatMessageVisibilityModel,
+			InputTokens:         sql.NullInt64{},
+			OutputTokens:        sql.NullInt64{},
+			TotalTokens:         sql.NullInt64{},
+			ReasoningTokens:     sql.NullInt64{},
+			CacheCreationTokens: sql.NullInt64{},
+			CacheReadTokens:     sql.NullInt64{},
+			ContextLimit:        sql.NullInt64{},
+			Compressed:          sql.NullBool{},
+			TotalCostMicros:     sql.NullInt64{},
+		})
+		if err != nil {
+			return xerrors.Errorf("insert workspace awareness message: %w", err)
+		}
+
 		userContent, err := chatprompt.MarshalParts(opts.InitialUserContent)
 		if err != nil {
 			return xerrors.Errorf("marshal initial user content: %w", err)

coderd/chatd/chatd_test.go

@@ -591,6 +591,97 @@ func TestEditMessageUpdatesAndTruncatesAndClearsQueue(t *testing.T) {
 	require.False(t, chatFromDB.WorkerID.Valid)
 }
 
+func TestCreateChatInsertsWorkspaceAwarenessMessage(t *testing.T) {
+	t.Parallel()
+
+	t.Run("WithWorkspace", func(t *testing.T) {
+		t.Parallel()
+
+		db, ps := dbtestutil.NewDB(t)
+		server := newTestServer(t, db, ps, uuid.New())
+
+		ctx := testutil.Context(t, testutil.WaitLong)
+		user, model := seedChatDependencies(ctx, t, db)
+
+		org := dbgen.Organization(t, db, database.Organization{})
+		tv := dbgen.TemplateVersion(t, db, database.TemplateVersion{
+			OrganizationID: org.ID,
+			CreatedBy:      user.ID,
+		})
+		tpl := dbgen.Template(t, db, database.Template{
+			CreatedBy:       user.ID,
+			OrganizationID:  org.ID,
+			ActiveVersionID: tv.ID,
+		})
+		workspace := dbgen.Workspace(t, db, database.WorkspaceTable{
+			OwnerID:        user.ID,
+			OrganizationID: org.ID,
+			TemplateID:     tpl.ID,
+		})
+
+		chat, err := server.CreateChat(ctx, chatd.CreateOptions{
+			OwnerID:            user.ID,
+			WorkspaceID:        uuid.NullUUID{UUID: workspace.ID, Valid: true},
+			Title:              "test-with-workspace",
+			ModelConfigID:      model.ID,
+			InitialUserContent: []codersdk.ChatMessagePart{codersdk.ChatMessageText("hello")},
+		})
+		require.NoError(t, err)
+
+		messages, err := db.GetChatMessagesForPromptByChatID(ctx, chat.ID)
+		require.NoError(t, err)
+
+		var workspaceMsg *database.ChatMessage
+		for _, msg := range messages {
+			if msg.Role == database.ChatMessageRoleSystem {
+				content := string(msg.Content.RawMessage)
+				if strings.Contains(content, "attached to a workspace") {
+					workspaceMsg = &msg
+					break
+				}
+			}
+		}
+		require.NotNil(t, workspaceMsg, "workspace awareness system message should exist")
+		require.Equal(t, database.ChatMessageRoleSystem, workspaceMsg.Role)
+		require.Equal(t, database.ChatMessageVisibilityModel, workspaceMsg.Visibility)
+	})
+
+	t.Run("WithoutWorkspace", func(t *testing.T) {
+		t.Parallel()
+
+		db, ps := dbtestutil.NewDB(t)
+		server := newTestServer(t, db, ps, uuid.New())
+
+		ctx := testutil.Context(t, testutil.WaitLong)
+		user, model := seedChatDependencies(ctx, t, db)
+
+		chat, err := server.CreateChat(ctx, chatd.CreateOptions{
+			OwnerID:            user.ID,
+			Title:              "test-without-workspace",
+			ModelConfigID:      model.ID,
+			InitialUserContent: []codersdk.ChatMessagePart{codersdk.ChatMessageText("hello")},
+		})
+		require.NoError(t, err)
+
+		messages, err := db.GetChatMessagesForPromptByChatID(ctx, chat.ID)
+		require.NoError(t, err)
+
+		var workspaceMsg *database.ChatMessage
+		for _, msg := range messages {
+			if msg.Role == database.ChatMessageRoleSystem {
+				content := string(msg.Content.RawMessage)
+				if strings.Contains(content, "no workspace associated") {
+					workspaceMsg = &msg
+					break
+				}
+			}
+		}
+		require.NotNil(t, workspaceMsg, "workspace awareness system message should exist")
+		require.Equal(t, database.ChatMessageRoleSystem, workspaceMsg.Role)
+		require.Equal(t, database.ChatMessageVisibilityModel, workspaceMsg.Visibility)
+	})
+}
+
 func TestCreateChatRejectsWhenUsageLimitReached(t *testing.T) {
 	t.Parallel()