Function copyParentContextMessages

coderd/x/chatd/subagent.go:1125–1207

copyParentContextMessages reads persisted context-file and skill messages from the parent chat and inserts copies into the child chat. This ensures sub-agents inherit the same instruction and skill context as their parent without independently re-fetching from the agent.

(
	ctx context.Context,
	logger slog.Logger,
	store database.Store,
	parent database.Chat,
	child database.Chat,
)

// skill context as their parent without independently re-fetching
// from the agent.
func copyParentContextMessages(
	ctx context.Context,
	logger slog.Logger,
	store database.Store,
	parent database.Chat,
	child database.Chat,
) ([]codersdk.ChatMessagePart, error) {
	parentMessages, err := store.GetChatMessagesByChatID(ctx, database.GetChatMessagesByChatIDParams{
		ChatID:  parent.ID,
		AfterID: 0,
	})
	if err != nil {
		return nil, xerrors.Errorf("get parent messages: %w", err)
	}

	var (
		copiedParts      []codersdk.ChatMessagePart
		copiedRole       database.ChatMessageRole
		copiedVisibility database.ChatMessageVisibility
		copiedVersion    int16
	)
	for _, msg := range parentMessages {
		if !msg.Content.Valid {
			continue
		}
		var parts []codersdk.ChatMessagePart
		if err := json.Unmarshal(msg.Content.RawMessage, &parts); err != nil {
			logger.Warn(ctx, "failed to unmarshal parent context message",
				slog.F("parent_chat_id", parent.ID),
				slog.F("message_id", msg.ID),
				slog.Error(err),
			)
			continue
		}

		messageContextParts := FilterContextParts(parts, true)
		if len(messageContextParts) == 0 {
			continue
		}
		if copiedParts == nil {
			copiedRole = msg.Role
			copiedVisibility = msg.Visibility
			copiedVersion = msg.ContentVersion
		}
		copiedParts = append(copiedParts, messageContextParts...)
	}
	if len(copiedParts) == 0 {
		return nil, nil
	}

	copiedParts = FilterContextPartsToLatestAgent(copiedParts)
	filteredContent, err := chatprompt.MarshalParts(copiedParts)
	if err != nil {
		return nil, xerrors.Errorf("marshal filtered context parts: %w", err)
	}

	msgParams := database.InsertChatMessagesParams{ //nolint:exhaustruct // Fields populated by append[User]ChatMessage.
		ChatID: child.ID,