coder/coderd/x/chatd/subagent.go

package chatd

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"slices"
	"strings"
	"time"

	"charm.land/fantasy"
	"github.com/google/uuid"
	"github.com/sqlc-dev/pqtype"
	"golang.org/x/xerrors"

	"cdr.dev/slog/v3"
	"github.com/coder/coder/v2/coderd/database"
	"github.com/coder/coder/v2/coderd/database/dbauthz"
	dbpubsub "github.com/coder/coder/v2/coderd/database/pubsub"
	coderdpubsub "github.com/coder/coder/v2/coderd/pubsub"
	"github.com/coder/coder/v2/coderd/util/ptr"
	"github.com/coder/coder/v2/coderd/x/agenthooks/dispatch"
	"github.com/coder/coder/v2/coderd/x/chatd/chathooks"
	"github.com/coder/coder/v2/coderd/x/chatd/chatprompt"
	"github.com/coder/coder/v2/coderd/x/chatd/chatprovider"
	"github.com/coder/coder/v2/coderd/x/chatd/chatstate"
	"github.com/coder/coder/v2/codersdk"
	"github.com/coder/coder/v2/codersdk/workspacesdk"
	"github.com/coder/coder/v2/codersdk/x/agenthooks"
)

var ErrSubagentNotDescendant = xerrors.New("target chat is not a descendant of current chat")

// ErrSubagentWaitTimeout is returned by awaitSubagentCompletion when the
// wait deadline elapses before the subagent reaches a terminal status. The
// agent is still working and the wait can be retried.
var ErrSubagentWaitTimeout = xerrors.New("timed out waiting for delegated subagent completion")

// subagentToolNameAliases maps deprecated subagent tool names to their
// current names so historical close_agent calls in chat history still
// dispatch to interrupt_agent without advertising the old name in the
// tool list.
var subagentToolNameAliases = map[string]string{
	"close_agent": "interrupt_agent",
}

// subagentStatusError wraps a subagent that reached error status. It
// carries the chat and report so callers can surface a structured,
// recoverable-aware payload instead of a bare tool error.
type subagentStatusError struct {
	chat   database.Chat
	report string
	reason string
}

func (e *subagentStatusError) Error() string { return e.reason }

const (
	subagentAwaitPollInterval  = 200 * time.Millisecond
	subagentAwaitFallbackPoll  = 5 * time.Second
	defaultSubagentWaitTimeout = 5 * time.Minute

	defaultListAgentsLimit       = 10
	maxListAgentsLimit           = 50
	subagentRecordingStopTimeout = 90 * time.Second
)

// computerUseSubagentSystemPrompt is the system prompt prepended to
// every computer use subagent chat. It instructs the model on how to
// interact with the desktop environment via the computer tool.
const computerUseSubagentSystemPrompt = `You are a computer use agent with access to a desktop environment. You can see the screen, move the mouse, click, type, scroll, and drag.

Your primary tool is the "computer" tool which lets you interact with the desktop. After every action you take, you will receive a screenshot showing the current state of the screen. Use these screenshots to verify your actions and plan next steps.

Guidelines:
- Always start by taking a screenshot to see the current state of the desktop.
- Use wait or ordinary actions when you only need a screenshot for your own reasoning.
- Use an explicit screenshot action when you want to share a durable screenshot with the user; those screenshots are attached to the chat automatically.
- Be precise with coordinates when clicking or typing.
- Wait for UI elements to load before interacting with them.
- If an action doesn't produce the expected result, try alternative approaches.
- Report what you accomplished when done.`

type waitAgentArgs struct {
	ChatID         string `json:"chat_id"`
	TimeoutSeconds *int   `json:"timeout_seconds,omitempty" description:"Defaults to 5 minutes."`
}

type messageAgentArgs struct {
	ChatID    string `json:"chat_id"`
	Message   string `json:"message"`
	Interrupt bool   `json:"interrupt,omitempty"`
}

type interruptAgentArgs struct {
	ChatID string `json:"chat_id"`
}

type listAgentsArgs struct {
	Limit  *int `json:"limit,omitempty"`
	Offset *int `json:"offset,omitempty"`
}

type listSubagentModelsArgs struct{}

func subagentModelOverrideLogLabel(
	overrideContext codersdk.ChatModelOverrideContext,
) string {
	switch overrideContext {
	case codersdk.ChatModelOverrideContextGeneral:
		return "general delegated child"
	case codersdk.ChatModelOverrideContextExplore:
		return "explore"
	default:
		return string(overrideContext)
	}
}

func personalModelOverrideContextForSubagent(
	overrideContext codersdk.ChatModelOverrideContext,
) (codersdk.ChatPersonalModelOverrideContext, error) {
	switch overrideContext {
	case codersdk.ChatModelOverrideContextGeneral:
		return codersdk.ChatPersonalModelOverrideContextGeneral, nil
	case codersdk.ChatModelOverrideContextExplore:
		return codersdk.ChatPersonalModelOverrideContextExplore, nil
	default:
		return "", xerrors.Errorf(
			"unknown subagent model override context %q",
			overrideContext,
		)
	}
}

func (p *Server) resolvePersonalSubagentModelConfigID(
	ctx context.Context,
	ownerID uuid.UUID,
	organizationID uuid.UUID,
	overrideContext codersdk.ChatModelOverrideContext,
) (uuid.UUID, *string, bool, error) {
	personalContext, err := personalModelOverrideContextForSubagent(overrideContext)
	if err != nil {
		return uuid.Nil, nil, false, err
	}
	override, err := p.db.GetChatUserModelOverride(ctx, database.GetChatUserModelOverrideParams{
		UserID:         ownerID,
		OrganizationID: organizationID,
		Context:        string(personalContext),
	})
	if err != nil {
		if !xerrors.Is(err, sql.ErrNoRows) {
			return uuid.Nil, nil, false, xerrors.Errorf(
				"get %s personal model override: %w",
				subagentModelOverrideLogLabel(overrideContext),
				err,
			)
		}
		return uuid.Nil, nil, false, nil
	}

	switch codersdk.ChatPersonalModelOverrideMode(override.Mode) {
	case codersdk.ChatPersonalModelOverrideModeChatDefault:
		return uuid.Nil, nil, true, nil
	case codersdk.ChatPersonalModelOverrideModeDeploymentDefault:
	case codersdk.ChatPersonalModelOverrideModeModel:
		if !override.ModelConfigID.Valid {
			p.logger.Warn(ctx,
				"personal model override has no model config, using deployment default",
				slog.F("override_context", overrideContext),
				slog.F("owner_id", ownerID),
			)
			break
		}
		modelConfig, ok, err := p.resolvePersonalModelOverride(
			ctx,
			overrideContext,
			ownerID,
			override.ModelConfigID.UUID,
		)
		if err != nil {
			return uuid.Nil, nil, false, err
		}
		if ok {
			return modelConfig.ID, ptr.FromNullString(override.ReasoningEffort), true, nil
		}
	default:
		p.logger.Warn(ctx,
			"unsupported personal model override mode, using deployment default",
			slog.F("override_context", overrideContext),
			slog.F("owner_id", ownerID),
			slog.F("mode", override.Mode),
		)
	}
	return uuid.Nil, nil, false, nil
}

func (p *Server) resolvePersonalModelOverride(
	ctx context.Context,
	overrideContext codersdk.ChatModelOverrideContext,
	ownerID uuid.UUID,
	modelConfigID uuid.UUID,
) (database.ChatModelConfig, bool, error) {
	modelConfig, providerName, err := p.resolveModelConfigAndNormalizedProvider(ctx, ownerID, modelConfigID)
	if err != nil {
		switch {
		case xerrors.Is(err, sql.ErrNoRows):
			p.logger.Debug(ctx,
				"personal model override is unavailable, using deployment default",
				slog.F("override_context", overrideContext),
				slog.F("owner_id", ownerID),
				slog.F("model_config_id", modelConfigID),
			)
		case errors.Is(err, errInvalidModelOverrideMetadata):
			p.logger.Debug(ctx,
				"personal model override metadata is invalid, using deployment default",
				slog.F("override_context", overrideContext),
				slog.F("owner_id", ownerID),
				slog.F("model_config_id", modelConfigID),
				slog.Error(err),
			)
		default:
			p.logger.Warn(ctx,
				"failed to resolve personal model override, using deployment default",
				slog.F("override_context", overrideContext),
				slog.F("owner_id", ownerID),
				slog.F("model_config_id", modelConfigID),
				slog.Error(err),
			)
		}
		return database.ChatModelConfig{}, false, nil
	}
	providerKeys, err := p.resolveUserProviderAPIKeys(ctx, ownerID, modelConfigAIProviderID(modelConfig))
	if err != nil {
		return database.ChatModelConfig{}, false, xerrors.Errorf("resolve provider API keys: %w", err)
	}
	if !userCanUseProviderKeys(providerKeys, providerName) {
		p.logger.Debug(ctx,
			"personal model override credentials are unavailable, using deployment default",
			slog.F("override_context", overrideContext),
			slog.F("owner_id", ownerID),
			slog.F("model_config_id", modelConfigID),
			slog.F("provider", providerName),
		)
		return database.ChatModelConfig{}, false, nil
	}
	return modelConfig, true, nil
}

func (p *Server) resolveSubagentModelConfigID(
	ctx context.Context,
	ownerID uuid.UUID,
	organizationID uuid.UUID,
	overrideContext codersdk.ChatModelOverrideContext,
) (uuid.UUID, *string, error) {
	//nolint:gocritic // Chatd needs its scoped config and user-data access here.
	chatdCtx := dbauthz.AsChatd(ctx)
	personalOverridesEnabled, err := p.db.GetChatPersonalModelOverridesEnabled(chatdCtx)
	if err != nil {
		return uuid.Nil, nil, xerrors.Errorf("get chat personal model overrides enabled: %w", err)
	}
	if personalOverridesEnabled {
		modelConfigID, reasoningEffort, resolved, err := p.resolvePersonalSubagentModelConfigID(
			chatdCtx,
			ownerID,
			organizationID,
			overrideContext,
		)
		if err != nil {
			return uuid.Nil, nil, err
		}
		if resolved {
			return modelConfigID, reasoningEffort, nil
		}
	}

	switch overrideContext {
	case codersdk.ChatModelOverrideContextGeneral,
		codersdk.ChatModelOverrideContextExplore:
	default:
		return uuid.Nil, nil, xerrors.Errorf(
			"unsupported subagent model override context %q",
			overrideContext,
		)
	}

	resolved, err := p.resolveModelOverride(chatdCtx, modelOverrideSpec{
		context:         string(overrideContext),
		ownerID:         ownerID,
		organizationID:  organizationID,
		queryFailure:    modelOverrideFailureModeHard,
		configFailure:   modelOverrideFailureModeSoft,
		providerFailure: modelOverrideFailureModeSoft,
	})
	if err != nil {
		return uuid.Nil, nil, err
	}
	if !resolved.Set {
		return uuid.Nil, nil, nil
	}
	return resolved.Config.ID, resolved.ReasoningEffort, nil
}

func (p *Server) resolveExplicitSpawnOverrides(
	ctx context.Context,
	ownerID uuid.UUID,
	organizationID uuid.UUID,
	args spawnAgentArgs,
) (*uuid.UUID, *string, error) {
	var explicitModelConfigID *uuid.UUID
	if raw := strings.TrimSpace(args.ModelConfigID); raw != "" {
		modelConfigID, err := uuid.Parse(raw)
		if err != nil {
			return nil, nil, xerrors.New(
				"invalid model_config_id: must be a valid UUID; use " +
					listSubagentModelsToolName + " to see available models",
			)
		}
		modelConfig, providerName, err := p.resolveModelConfigForOrganization(
			ctx,
			ownerID,
			organizationID,
			modelConfigID,
		)
		if err != nil {
			switch {
			case errors.Is(err, sql.ErrNoRows):
				return nil, nil, xerrors.New(
					"model_config_id not found or is disabled; use " +
						listSubagentModelsToolName + " to see available models",
				)
			case errors.Is(err, errInvalidModelOverrideMetadata):
				return nil, nil, xerrors.Errorf(
					"model_config_id metadata is invalid: %w",
					err,
				)
			default:
				p.logger.Warn(ctx, "failed to resolve spawn_agent model_config_id",
					slog.F("model_config_id", modelConfigID),
					slog.Error(err),
				)
				return nil, nil, xerrors.New("internal error looking up model config")
			}
		}
		//nolint:gocritic // Provider credentials remain privileged Chatd reads.
		providerKeys, err := p.resolveUserProviderAPIKeys(
			dbauthz.AsChatd(ctx),
			ownerID,
			modelConfigAIProviderID(modelConfig),
		)
		if err != nil {
			p.logger.Warn(ctx, "failed to resolve provider API keys for spawn_agent model_config_id",
				slog.F("model_config_id", modelConfigID),
				slog.Error(err),
			)
			return nil, nil, xerrors.New("internal error looking up model config")
		}
		if !userCanUseProviderKeys(providerKeys, providerName) {
			return nil, nil, xerrors.Errorf(
				"model_config_id credentials are unavailable for provider %q",
				providerName,
			)
		}
		explicitModelConfigID = &modelConfig.ID
	}

	var explicitReasoningEffort *string
	if raw := strings.TrimSpace(args.ReasoningEffort); raw != "" {
		effort := strings.ToLower(raw)
		if !chatprovider.IsValidReasoningEffort(effort) {
			return nil, nil, xerrors.Errorf(
				"invalid reasoning_effort: must be one of %s",
				strings.Join(codersdk.ChatModelReasoningEffortValues(), ", "),
			)
		}
		explicitReasoningEffort = &effort
	}

	return explicitModelConfigID, explicitReasoningEffort, nil
}

func (p *Server) listSpawnableModelConfigs(
	ctx context.Context,
	ownerID uuid.UUID,
	organizationID uuid.UUID,
) ([]map[string]any, error) {
	modelCtx, err := p.callerModelConfigContext(ctx, ownerID)
	if err != nil {
		return nil, err
	}
	rows, err := enabledChatModelConfigsForOrganization(modelCtx, p.db, organizationID)
	if err != nil {
		return nil, xerrors.Errorf("get enabled chat model configs: %w", err)
	}
	models := make([]map[string]any, 0, len(rows))
	providerKeysByID := make(map[uuid.UUID]chatprovider.ProviderAPIKeys)
	for _, row := range rows {
		providerName := chatprovider.NormalizeProvider(row.Provider)
		if providerName == "" {
			continue
		}
		if _, _, err := chatprovider.ResolveModelWithProviderHint(
			row.ChatModelConfig.Model,
			providerName,
		); err != nil {
			continue
		}
		providerID := modelConfigAIProviderID(row.ChatModelConfig)
		providerKeys, ok := providerKeysByID[providerID]
		if !ok {
			//nolint:gocritic // Provider credentials remain privileged Chatd reads.
			providerKeys, err = p.resolveUserProviderAPIKeys(
				dbauthz.AsChatd(ctx),
				ownerID,
				providerID,
			)
			if err != nil {
				return nil, xerrors.Errorf("resolve provider API keys: %w", err)
			}
			providerKeysByID[providerID] = providerKeys
		}
		if !userCanUseProviderKeys(providerKeys, providerName) {
			continue
		}
		entry := map[string]any{
			"model_config_id": row.ChatModelConfig.ID.String(),
			"display_name":    row.ChatModelConfig.DisplayName,
			"model":           row.ChatModelConfig.Model,
			"provider":        providerName,
			"context_limit":   row.ChatModelConfig.ContextLimit,
			"is_default":      row.ChatModelConfig.IsDefault,
		}
		callConfig := codersdk.ChatModelCallConfig{}
		if len(row.ChatModelConfig.Options) > 0 {
			if err := json.Unmarshal(row.ChatModelConfig.Options, &callConfig); err == nil {
				if efforts := chatprovider.SelectableReasoningEfforts(callConfig.ReasoningEffort); len(efforts) > 0 {
					entry["reasoning_efforts"] = efforts
				}
			}
		}
		models = append(models, entry)
	}
	return models, nil
}

func (p *Server) subagentTools(
	ctx context.Context,
	currentChat func() database.Chat,
	currentModelConfigID uuid.UUID,
) []fantasy.AgentTool {
	currentChatSnapshot := database.Chat{}
	if currentChat != nil {
		currentChatSnapshot = currentChat()
	}

	spawnAgentDescription := buildSpawnAgentDescription(
		ctx,
		p,
		currentChatSnapshot,
	)

	return []fantasy.AgentTool{
		fantasy.NewAgentTool(
			spawnAgentToolName,
			spawnAgentDescription,
			func(ctx context.Context, args spawnAgentArgs, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
				if currentChat == nil {
					return fantasy.NewTextErrorResponse("subagent callbacks are not configured"), nil
				}

				parent, err := p.loadSubagentSpawnParentChat(ctx, currentChat)
				if err != nil {
					return fantasy.NewTextErrorResponse(err.Error()), nil
				}

				definition, err := resolveSubagentDefinition(
					ctx,
					p,
					parent,
					args.Type,
				)
				if err != nil {
					return fantasy.NewTextErrorResponse(err.Error()), nil
				}

				if definition.id == subagentTypeComputerUse &&
					(strings.TrimSpace(args.ModelConfigID) != "" ||
						strings.TrimSpace(args.ReasoningEffort) != "") {
					return fantasy.NewTextErrorResponse(
						`model_config_id and reasoning_effort are not supported for type "` +
							subagentTypeComputerUse + `"`,
					), nil
				}

				explicitModelConfigID, explicitReasoningEffort, err := p.resolveExplicitSpawnOverrides(
					ctx,
					parent.OwnerID,
					parent.OrganizationID,
					args,
				)
				if err != nil {
					return fantasy.NewTextErrorResponse(err.Error()), nil
				}

				turnParent := currentChatSnapshot
				if turnParent.ID == uuid.Nil {
					turnParent = parent
				}

				options, err := definition.buildOptions(
					ctx,
					p,
					parent,
					turnParent,
					currentModelConfigID,
					explicitModelConfigID,
					args.Prompt,
				)
				if err != nil {
					return fantasy.NewTextErrorResponse(err.Error()), nil
				}

				if explicitReasoningEffort != nil {
					options.reasoningEffortOverride = explicitReasoningEffort
				}

				childChat, err := p.createChildSubagentChatWithOptions(
					ctx,
					parent,
					args.Prompt,
					args.Title,
					options,
				)
				if err != nil {
					// A failed hook dispatch must fail closed instead of
					// degrading into a tool error the model can ignore.
					if _, ok := errors.AsType[*dispatch.Error](err); ok {
						return fantasy.ToolResponse{}, err
					}
					// chathooks.UserPromptDeniedError.Error() carries the user-facing
					// denial message, so the model can adjust its prompt.
					return fantasy.NewTextErrorResponse(err.Error()), nil
				}

				return toolJSONResponse(withSubagentType(map[string]any{
					"chat_id": childChat.ID.String(),
					"title":   childChat.Title,
					"status":  string(childChat.Status),
				}, childChat)), nil
			},
		),
		fantasy.NewAgentTool(
			listSubagentModelsToolName,
			"List the enabled model configurations available for "+
				spawnAgentToolName+"'s model_config_id argument. Only models "+
				"usable with the chat owner's credentials are returned. Each "+
				"entry includes model_config_id, display_name, model, "+
				"provider, context_limit, is_default, and reasoning_efforts "+
				"(the values accepted by "+spawnAgentToolName+"'s "+
				"reasoning_effort for that model).",
			func(ctx context.Context, _ listSubagentModelsArgs, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
				if currentChat == nil {
					return fantasy.NewTextErrorResponse("subagent callbacks are not configured"), nil
				}

				parent, err := p.loadSubagentSpawnParentChat(ctx, currentChat)
				if err != nil {
					return fantasy.NewTextErrorResponse(err.Error()), nil
				}

				models, err := p.listSpawnableModelConfigs(ctx, parent.OwnerID, parent.OrganizationID)
				if err != nil {
					p.logger.Warn(ctx, "failed to list spawnable model configs",
						slog.F("chat_id", parent.ID),
						slog.Error(err),
					)
					return fantasy.NewTextErrorResponse("internal error listing model configs"), nil
				}

				return toolJSONResponse(map[string]any{
					"models": models,
				}), nil
			},
		),
		fantasy.NewAgentTool(
			"wait_agent",
			"Wait for a spawned child agent to finish and return its response "+
				"and status. Returns immediately when the agent finishes, even if "+
				"a longer timeout is set. A timeout does not stop the child; it "+
				"still owns its task. Wait again or check its status with "+
				"list_agents; do not take over its work without an acknowledged "+
				"handoff.",
			func(ctx context.Context, args waitAgentArgs, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
				if currentChat == nil {
					return fantasy.NewTextErrorResponse("subagent callbacks are not configured"), nil
				}

				targetChatID, err := parseSubagentToolChatID(args.ChatID)
				if err != nil {
					return fantasy.NewTextErrorResponse(err.Error()), nil
				}

				timeout := defaultSubagentWaitTimeout
				if args.TimeoutSeconds != nil {
					timeout = time.Duration(*args.TimeoutSeconds) * time.Second
				}

				parent := currentChat()
				var targetChatInfo *database.Chat
				if chat, lookupErr := p.db.GetChatByID(ctx, targetChatID); lookupErr == nil {
					targetChatInfo = &chat
				} else if !xerrors.Is(lookupErr, sql.ErrNoRows) {
					p.logger.Warn(ctx, "unexpected error looking up chat for recording",
						slog.F("chat_id", targetChatID),
						slog.Error(lookupErr),
					)
				}

				// Authorize: the target chat must be a descendant
				// of the current (parent) chat.
				isDescendant, descErr := isSubagentDescendant(ctx, p.db, parent.ID, targetChatID)
				if descErr != nil {
					return subagentErrorResponse(
						xerrors.New(fmt.Sprintf("failed to verify subagent relationship: %v", descErr)),
						targetChatInfo,
					), nil
				}
				if !isDescendant {
					return subagentErrorResponse(
						ErrSubagentNotDescendant,
						targetChatInfo,
					), nil
				}

				// Check if the target is a computer_use subagent
				// and start a desktop recording. Failures are
				// best-effort warnings. Recording never blocks
				// the wait_agent flow.
				var recordingID string
				var agentConn workspacesdk.AgentConn

				isComputerUseChat := targetChatInfo != nil &&
					targetChatInfo.Mode.Valid &&
					targetChatInfo.Mode.ChatMode == database.ChatModeComputerUse &&
					targetChatInfo.AgentID.Valid
				canRecord := isComputerUseChat && p.agentConnFn != nil

				if canRecord {
					conn, closeFn, connErr := p.agentConnFn(ctx, targetChatInfo.AgentID.UUID)
					if connErr == nil {
						agentConn = conn
						defer closeFn()

						recordingID = targetChatID.String()
						startErr := conn.StartDesktopRecording(ctx,
							workspacesdk.StartDesktopRecordingRequest{RecordingID: recordingID})
						if startErr != nil {
							p.logger.Warn(ctx, "failed to start desktop recording",
								slog.Error(startErr))
							recordingID = ""
						}
					} else {
						p.logger.Warn(ctx, "failed to get agent conn for recording",
							slog.Error(connErr))
					}
				}

				targetChat, report, awaitErr := p.awaitSubagentCompletion(
					ctx, parent.ID, targetChatID, timeout,
				)

				// On timeout or error, leave the recording running on
				// the agent so the next wait_agent call continues it.
				if awaitErr != nil {
					if xerrors.Is(awaitErr, ErrSubagentWaitTimeout) {
						// The agent may have completed in the gap between
						// the last poll and the timer firing. Re-check
						// completion with a fresh DB read to avoid acting
						// on a stale status (TOCTOU).
						checkedChat, checkedReport, done, checkErr := p.checkSubagentCompletion(ctx, targetChatID)
						if checkErr != nil {
							return subagentErrorResponse(checkErr, targetChatInfo), nil
						}
						if !done {
							return toolJSONResponse(withSubagentType(map[string]any{
								"chat_id":   targetChatID.String(),
								"title":     checkedChat.Title,
								"status":    string(checkedChat.Status),
								"timed_out": true,
							}, checkedChat)), nil
						}
						// The agent completed in the gap. Classify through
						// the same handler as the normal poll path. If the
						// agent errored, handleSubagentDone returns a
						// subagentStatusError that the error-status block
						// below catches.
						targetChat, report, awaitErr = handleSubagentDone(checkedChat, checkedReport)
						if awaitErr == nil {
							return p.waitAgentSuccessResponse(ctx, recordingID, agentConn, parent, targetChat, report), nil
						}
					}
					if errStatus, ok := errors.AsType[*subagentStatusError](awaitErr); ok {
						errChat := errStatus.chat
						decoded, lastError := subagentLastError(errChat.LastError)
						if lastError == "" {
							lastError = errStatus.reason
						}
						payload := map[string]any{
							"chat_id":    errChat.ID.String(),
							"title":      errChat.Title,
							"status":     string(errChat.Status),
							"last_error": lastError,
							"report":     errStatus.report,
						}
						if decoded != nil {
							kind := decoded.Kind
							if kind == "" {
								kind = codersdk.ChatErrorKindGeneric
							}
							payload["last_error_kind"] = string(kind)
							payload["last_error_retryable"] = decoded.Retryable
							if decoded.Detail != "" {
								payload["last_error_detail"] = decoded.Detail
							}
						}
						return toolJSONResponse(withSubagentType(payload, errChat)), nil
					}
					return subagentErrorResponse(awaitErr, targetChatInfo), nil
				}

				// Only stop and store the recording on success.
				return p.waitAgentSuccessResponse(ctx, recordingID, agentConn, parent, targetChat, report), nil
			},
		),
		fantasy.NewAgentTool(
			"message_agent",
			"Send a follow-up message to a previously spawned child "+
				"agent. If the agent is idle, it resumes work on the "+
				"message. If it is busy, the message is queued behind its "+
				"current work and any earlier queued messages; set interrupt "+
				"to true for corrections, changed scope, or a handoff that "+
				"returns the child's task to you, so its current work stops "+
				"first. Interrupting does not clear earlier queued messages, "+
				"and the tool result does not confirm the child has stopped. "+
				"Use wait_agent to collect the child's response. A handoff is "+
				"acknowledged only when wait_agent returns the child's response "+
				"to your handoff message; a message_agent result or an "+
				"interrupting status is not an acknowledgment.",
			func(ctx context.Context, args messageAgentArgs, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
				if currentChat == nil {
					return fantasy.NewTextErrorResponse("subagent callbacks are not configured"), nil
				}

				targetChatID, err := parseSubagentToolChatID(args.ChatID)
				if err != nil {
					return fantasy.NewTextErrorResponse(err.Error()), nil
				}

				parent := currentChat()
				var targetChatInfo *database.Chat
				if chat, lookupErr := p.db.GetChatByID(ctx, targetChatID); lookupErr == nil {
					targetChatInfo = &chat
				} else if !xerrors.Is(lookupErr, sql.ErrNoRows) {
					p.logger.Warn(ctx, "unexpected error looking up chat for message",
						slog.F("chat_id", targetChatID),
						slog.Error(lookupErr),
					)
				}
				busyBehavior := SendMessageBusyBehaviorQueue
				if args.Interrupt {
					busyBehavior = SendMessageBusyBehaviorInterrupt
				}
				targetChat, err := p.sendSubagentMessage(
					ctx,
					parent.ID,
					targetChatID,
					args.Message,
					busyBehavior,
				)
				if err != nil {
					return subagentErrorResponse(err, targetChatInfo), nil
				}

				interrupted := false
				if args.Interrupt && targetChatInfo != nil {
					interrupted = targetChatInfo.Status == database.ChatStatusRunning
				}
				return toolJSONResponse(withSubagentType(map[string]any{
					"chat_id":     targetChat.ID.String(),
					"title":       targetChat.Title,
					"status":      string(targetChat.Status),
					"interrupted": interrupted,
				}, targetChat)), nil
			},
		),
		fantasy.NewAgentTool(
			"interrupt_agent",
			"Interrupt a spawned child agent's current work. The "+
				"status may briefly read interrupting before transitioning "+
				"to waiting, or running if there are queued messages. "+
				"Resume with message_agent or leave it idle.",
			func(ctx context.Context, args interruptAgentArgs, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
				if currentChat == nil {
					return fantasy.NewTextErrorResponse("subagent callbacks are not configured"), nil
				}

				targetChatID, err := parseSubagentToolChatID(args.ChatID)
				if err != nil {
					return fantasy.NewTextErrorResponse(err.Error()), nil
				}

				parent := currentChat()
				var targetChatInfo *database.Chat
				if chat, lookupErr := p.db.GetChatByID(ctx, targetChatID); lookupErr == nil {
					targetChatInfo = &chat
				} else if !xerrors.Is(lookupErr, sql.ErrNoRows) {
					p.logger.Warn(ctx, "unexpected error looking up chat for interrupt",
						slog.F("chat_id", targetChatID),
						slog.Error(lookupErr),
					)
				}
				targetChat, interrupted, err := p.interruptSubagent(
					ctx,
					parent.ID,
					targetChatID,
				)
				if err != nil {
					return subagentErrorResponse(err, targetChatInfo), nil
				}

				return toolJSONResponse(withSubagentType(map[string]any{
					"chat_id":     targetChat.ID.String(),
					"title":       targetChat.Title,
					"interrupted": interrupted,
					"status":      string(targetChat.Status),
				}, targetChat)), nil
			},
		),
		fantasy.NewAgentTool(
			"list_agents",
			"List the child agents spawned by this chat, most recently "+
				"active first. Returns up to `limit` agents (default 10) "+
				"with `total` and `has_more`; use `offset` to page. The "+
				"sort order is best-effort: an agent's position may shift "+
				"if its updated_at changes between calls. Each "+
				"agent has chat_id, title, type, status, created_at, "+
				"updated_at. Status: running = working, "+
				"interrupting = transient, waiting = idle, "+
				"error = stopped on error.",
			func(ctx context.Context, args listAgentsArgs, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
				if currentChat == nil {
					return fantasy.NewTextErrorResponse("subagent callbacks are not configured"), nil
				}

				limit := defaultListAgentsLimit
				if args.Limit != nil {
					limit = min(max(*args.Limit, 1), maxListAgentsLimit)
				}
				offset := 0
				if args.Offset != nil && *args.Offset > 0 {
					offset = *args.Offset
				}

				parent := currentChat()
				if parent.ParentChatID.Valid {
					return fantasy.NewTextErrorResponse("list_agents is only available on root chats"), nil
				}
				rows, err := p.db.GetChildChatsByParentIDs(ctx, database.GetChildChatsByParentIDsParams{
					ParentIds: []uuid.UUID{parent.ID},
					// Exclude archived children by default. Do not pass an
					// invalid NullBool, which would include archived rows.
					Archived: sql.NullBool{Bool: false, Valid: true},
				})
				if err != nil {
					return fantasy.NewTextErrorResponse(xerrors.Errorf("list child agents: %w", err).Error()), nil
				}

				slices.SortStableFunc(rows, func(a, b database.GetChildChatsByParentIDsRow) int {
					if c := b.Chat.UpdatedAt.Compare(a.Chat.UpdatedAt); c != 0 {
						return c
					}
					return strings.Compare(b.Chat.ID.String(), a.Chat.ID.String())
				})

				total := len(rows)
				start := min(offset, total)
				end := min(start+limit, total)
				page := rows[start:end]

				agents := make([]map[string]any, 0, len(page))
				for _, row := range page {
					child := row.Chat
					agents = append(agents, withSubagentType(map[string]any{
						"chat_id":    child.ID.String(),
						"title":      child.Title,
						"status":     string(child.Status),
						"created_at": child.CreatedAt.Format(time.RFC3339),
						"updated_at": child.UpdatedAt.Format(time.RFC3339),
					}, child))
				}

				return toolJSONResponse(map[string]any{
					"agents":   agents,
					"total":    total,
					"returned": len(agents),
					"offset":   offset,
					"has_more": end < total,
				}), nil
			},
		),
	}
}

func (p *Server) loadSubagentSpawnParentChat(
	ctx context.Context,
	currentChat func() database.Chat,
) (database.Chat, error) {
	parent := currentChat()
	if err := validateSubagentSpawnParent(parent); err != nil {
		return database.Chat{}, err
	}
	reloadedParent, err := p.db.GetChatByID(ctx, parent.ID)
	if err != nil {
		p.logger.Warn(ctx, "failed to load parent chat for spawn_agent",
			slog.F("chat_id", parent.ID),
			slog.Error(err),
		)
		return database.Chat{}, xerrors.New("failed to load parent chat")
	}
	parent = reloadedParent
	if err := validateSubagentSpawnParent(parent); err != nil {
		return database.Chat{}, err
	}
	return parent, nil
}

func parseSubagentToolChatID(raw string) (uuid.UUID, error) {
	chatID, err := uuid.Parse(strings.TrimSpace(raw))
	if err != nil {
		return uuid.Nil, xerrors.New("chat_id must be a valid UUID")
	}
	return chatID, nil
}

// childSubagentChatOptions carries per-child overrides for subagent chat
// creation. modelConfigIDOverride, reasoningEffortOverride, and
// planModeOverride apply to any subagent. inheritedMCPServerIDs is an
// Explore-only snapshot of the spawning parent turn's effective external MCP
// entitlement. resolveExploreToolSnapshot computes and persists it on the
// child chat. Non-Explore children ignore this field.
type childSubagentChatOptions struct {
	chatMode                database.NullChatMode
	systemPrompt            string
	modelConfigIDOverride   *uuid.UUID
	reasoningEffortOverride *string
	planModeOverride        *database.NullChatPlanMode
	inheritedMCPServerIDs   []uuid.UUID
}

// resolveExploreToolSnapshot computes the child chat's inherited MCP
// server snapshot from the spawning parent turn.
//
// The MCP set is filtered in two stages. First,
// filterExternalMCPConfigsForTurn applies the parent turn's plan-mode
// policy to the parent's MCP configs, producing visibleConfigs. Second,
// if the parent is itself an Explore child, the visible set is narrowed to
// the parent's persisted MCPServerIDs so an Explore chain cannot
// re-escalate beyond the original grant. Non-Explore parents pass
// through the second stage unchanged.
func (p *Server) resolveExploreToolSnapshot(
	ctx context.Context,
	parent database.Chat,
) ([]uuid.UUID, error) {
	inheritedMCPServerIDs := []uuid.UUID{}
	if len(parent.MCPServerIDs) > 0 {
		configs, err := enabledMCPServerConfigsForChatOrg(ctx, p.db, parent.OrganizationID, parent.MCPServerIDs)
		if err != nil {
			return nil, xerrors.Errorf("get parent MCP server configs for chat %s: %w", parent.ID, err)
		}

		visibleConfigs, _ := filterExternalMCPConfigsForTurn(
			configs,
			parent.PlanMode,
			parent.ParentChatID,
		)
		// Empty means the parent is not Explore, so all plan-filtered
		// configs remain eligible. Populated means the parent is
		// Explore, so only its persisted snapshot can pass.
		allowedParentIDs := map[uuid.UUID]struct{}{}
		if isExploreSubagentMode(parent.Mode) {
			for _, id := range parent.MCPServerIDs {
				allowedParentIDs[id] = struct{}{}
			}
		}
		for _, cfg := range visibleConfigs {
			if len(allowedParentIDs) > 0 {
				if _, ok := allowedParentIDs[cfg.ID]; !ok {
					continue
				}
			}
			inheritedMCPServerIDs = append(inheritedMCPServerIDs, cfg.ID)
		}
	}

	return inheritedMCPServerIDs, nil
}

func (p *Server) createChildSubagentChatWithOptions(
	ctx context.Context,
	parent database.Chat,
	prompt string,
	title string,
	opts childSubagentChatOptions,
) (database.Chat, error) {
	if parent.ParentChatID.Valid {
		return database.Chat{}, xerrors.New("delegated chats cannot create child subagents")
	}

	prompt = strings.TrimSpace(prompt)
	if prompt == "" {
		return database.Chat{}, xerrors.New("prompt is required")
	}

	title = strings.TrimSpace(title)

	rootChatID := parent.ID
	if parent.RootChatID.Valid {
		rootChatID = parent.RootChatID.UUID
	}

	modelConfigID := parent.LastModelConfigID
	if opts.modelConfigIDOverride != nil {
		modelConfigID = *opts.modelConfigIDOverride
	}
	if modelConfigID == uuid.Nil {
		return database.Chat{}, xerrors.New("model config is required")
	}
	childPlanMode := parent.PlanMode
	if opts.planModeOverride != nil {
		childPlanMode = *opts.planModeOverride
	}

	mcpServerIDs := parent.MCPServerIDs
	if isExploreSubagentMode(opts.chatMode) {
		mcpServerIDs = slices.Clone(opts.inheritedMCPServerIDs)
	}
	if mcpServerIDs == nil {
		mcpServerIDs = []uuid.UUID{}
	}

	labelsJSON, err := json.Marshal(database.StringMap{})
	if err != nil {
		return database.Chat{}, xerrors.Errorf("marshal labels: %w", err)
	}
	childSystemPrompt := codersdk.SanitizePromptText(opts.systemPrompt)
	// Resolve the deployment prompt before opening the transaction so
	// child chat creation does not hold one DB connection while waiting
	// for another pool checkout.
	deploymentPrompt := p.resolveDeploymentSystemPrompt(ctx)
	// Delegated chats cannot call list_agents or message_agent, so
	// strip the root-only orchestration guidance from their prompt.
	deploymentPrompt = strings.Replace(deploymentPrompt, subagentOrchestrationPromptBlock, "", 1)

	// Review before persistence so spawned chats cannot bypass prompt policy.
	childChatID := uuid.New()
	var promptResult *chathooks.Result
	if p.hooks.Enabled() {
		mintedTurnID := uuid.New()
		promptMessage, err := chathooks.UserPromptMessage([]codersdk.ChatMessagePart{codersdk.ChatMessageText(prompt)})
		if err != nil {
			return database.Chat{}, err
		}
		promptResult, err = p.hooks.Trigger(ctx, chathooks.Chat{
			ID:           childChatID,
			OwnerID:      parent.OwnerID,
			WorkspaceID:  parent.WorkspaceID,
			ParentChatID: uuid.NullUUID{UUID: parent.ID, Valid: true},
			RootChatID:   uuid.NullUUID{UUID: rootChatID, Valid: true},
			TurnID:       &mintedTurnID,
		}, promptMessage, agenthooks.EventUserPromptSubmit, dispatch.CapacityClassGeneration)
		if err != nil {
			return database.Chat{}, chathooks.UserPromptDenial(err)
		}
		override, overridden, overrideErr := chathooks.UserPromptOverride(promptResult)
		if overrideErr != nil {
			return database.Chat{}, overrideErr
		}
		if overridden {
			// The overridden prompt also feeds the fallback title below.
			prompt = override
		}
	}
	if title == "" {
		title = subagentFallbackChatTitle(prompt)
	}

	workspaceAwareness := workspaceDetachedNoCreateAwareness
	if parent.WorkspaceID.Valid {
		workspaceAwareness = workspaceAttachedAwareness
	}
	workspaceAwarenessContent, err := chatprompt.MarshalParts([]codersdk.ChatMessagePart{
		codersdk.ChatMessageText(workspaceAwareness),
	})
	if err != nil {
		return database.Chat{}, xerrors.Errorf("marshal workspace awareness: %w", err)
	}
	childUserParts := []codersdk.ChatMessagePart{codersdk.ChatMessageText(prompt)}
	childUserParts = append(childUserParts, chathooks.UserPromptParts(promptResult)...)
	userContent, err := chatprompt.MarshalParts(childUserParts)
	if err != nil {
		return database.Chat{}, xerrors.Errorf("marshal initial user content: %w", err)
	}

	initialMessages := make([]chatstate.Message, 0, 4)
	if deploymentPrompt != "" {
		deploymentContent, err := chatprompt.MarshalParts([]codersdk.ChatMessagePart{
			codersdk.ChatMessageText(deploymentPrompt),
		})
		if err != nil {
			return database.Chat{}, xerrors.Errorf("marshal deployment system prompt: %w", err)
		}
		initialMessages = append(initialMessages, systemMessage(deploymentContent, modelConfigID))
	}
	if childSystemPrompt != "" {
		childSystemPromptContent, err := chatprompt.MarshalParts([]codersdk.ChatMessagePart{
			codersdk.ChatMessageText(childSystemPrompt),
		})
		if err != nil {
			return database.Chat{}, xerrors.Errorf("marshal child system prompt: %w", err)
		}
		initialMessages = append(initialMessages, systemMessage(childSystemPromptContent, modelConfigID))
	}
	initialMessages = append(initialMessages, systemMessage(workspaceAwarenessContent, modelConfigID))

	// The child shares the parent's workspace and agent, so it inherits
	// workspace context the same way a top-level chat does: pinned from the
	// agent's latest snapshot (see hydrateChatContextOnCreate below). The
	// parent's context is not copied into child history.
	initialMessages = append(initialMessages, userMessage(userContent, modelConfigID, parent.OwnerID, opts.reasoningEffortOverride))

	publisher := p.pubsub
	if publisher == nil {
		publisher = dbpubsub.NewInMemory()
	}
	result, err := chatstate.CreateChatWithID(ctx, p.db, publisher, childChatID, chatstate.CreateChatInput{
		OrganizationID:    parent.OrganizationID,
		OwnerID:           parent.OwnerID,
		WorkspaceID:       parent.WorkspaceID,
		BuildID:           parent.BuildID,
		AgentID:           parent.AgentID,
		ParentChatID:      uuid.NullUUID{UUID: parent.ID, Valid: true},
		RootChatID:        uuid.NullUUID{UUID: rootChatID, Valid: true},
		LastModelConfigID: modelConfigID,
		Title:             title,
		Mode:              opts.chatMode,
		PlanMode:          childPlanMode,
		MCPServerIDs:      mcpServerIDs,
		Labels: pqtype.NullRawMessage{
			RawMessage: labelsJSON,
			Valid:      true,
		},
		DynamicTools:    pqtype.NullRawMessage{},
		ClientType:      parent.ClientType,
		InitialMessages: initialMessages,
		InitialStatus:   database.ChatStatusRunning,
	})
	if err != nil {
		return database.Chat{}, xerrors.Errorf("create child chat: %w", err)
	}

	child := result.Chat

	// Pin the child to its agent's latest context snapshot, mirroring the
	// top-level create path. The child shares the parent's workspace agent,
	// so this reproduces the parent's workspace context without copying it
	// through chat history.
	p.hydrateChatContextOnCreate(ctx, child)

	p.publishChatPubsubEvent(child, codersdk.ChatWatchEventKindCreated, nil)
	return child, nil
}

func (p *Server) sendSubagentMessage(
	ctx context.Context,
	parentChatID uuid.UUID,
	targetChatID uuid.UUID,
	message string,
	busyBehavior SendMessageBusyBehavior,
) (database.Chat, error) {
	message = strings.TrimSpace(message)
	if message == "" {
		return database.Chat{}, xerrors.New("message is required")
	}

	isDescendant, err := isSubagentDescendant(ctx, p.db, parentChatID, targetChatID)
	if err != nil {
		return database.Chat{}, err
	}
	if !isDescendant {
		return database.Chat{}, ErrSubagentNotDescendant
	}

	// Look up the target chat to get the owner for CreatedBy.
	targetChat, err := p.db.GetChatByID(ctx, targetChatID)
	if err != nil {
		return database.Chat{}, xerrors.Errorf("get target chat: %w", err)
	}

	sendResult, err := p.SendMessage(ctx, SendMessageOptions{
		ChatID:       targetChatID,
		CreatedBy:    targetChat.OwnerID,
		Content:      []codersdk.ChatMessagePart{codersdk.ChatMessageText(message)},
		BusyBehavior: busyBehavior,
	})
	if err != nil {
		return database.Chat{}, err
	}

	return sendResult.Chat, nil
}

func (p *Server) awaitSubagentCompletion(
	ctx context.Context,
	parentChatID uuid.UUID,
	targetChatID uuid.UUID,
	timeout time.Duration,
) (database.Chat, string, error) {
	isDescendant, err := isSubagentDescendant(ctx, p.db, parentChatID, targetChatID)
	if err != nil {
		return database.Chat{}, "", err
	}
	if !isDescendant {
		return database.Chat{}, "", ErrSubagentNotDescendant
	}

	// Check immediately before entering the poll loop.
	targetChat, report, done, checkErr := p.checkSubagentCompletion(ctx, targetChatID)
	if checkErr != nil {
		return database.Chat{}, "", checkErr
	}
	if done {
		return handleSubagentDone(targetChat, report)
	}

	if timeout <= 0 {
		timeout = defaultSubagentWaitTimeout
	}
	timer := p.clock.NewTimer(timeout, "chatd", "subagent_await")
	defer timer.Stop()

	// Subscribe for fast status notifications and use a less
	// aggressive fallback poll. If subscription fails, fall back to
	// the original 200ms polling.
	pollInterval := subagentAwaitFallbackPoll
	ch := make(chan struct{}, 1)
	notifyCh := (<-chan struct{})(ch)
	cancel, subErr := p.pubsub.SubscribeWithErr(
		coderdpubsub.ChatStateUpdateChannel(targetChatID),
		func(_ context.Context, _ []byte, _ error) {
			// Non-blocking send so we never stall the
			// pubsub dispatch goroutine.
			select {
			case ch <- struct{}{}:
			default:
			}
		},
	)
	if subErr == nil {
		defer cancel()
	} else {
		// Subscription failed; fall back to fast polling.
		pollInterval = subagentAwaitPollInterval
		notifyCh = nil
	}

	ticker := p.clock.NewTicker(pollInterval, "chatd", "subagent_poll")
	defer ticker.Stop()

	for {
		select {
		case <-notifyCh:
		case <-ticker.C:
		case <-timer.C:
			return database.Chat{}, "", ErrSubagentWaitTimeout
		case <-ctx.Done():
			return database.Chat{}, "", ctx.Err()
		}

		targetChat, report, done, checkErr = p.checkSubagentCompletion(ctx, targetChatID)
		if checkErr != nil {
			return database.Chat{}, "", checkErr
		}
		if done {
			return handleSubagentDone(targetChat, report)
		}
	}
}

// handleSubagentDone translates a completed subagent check into the
// appropriate return value. An error-status chat is returned as a typed
// subagentStatusError that carries the chat and report so the
// wait_agent handler can surface a structured, recoverable-aware payload.
func handleSubagentDone(
	chat database.Chat,
	report string,
) (database.Chat, string, error) {
	if chat.Status == database.ChatStatusError {
		reason := strings.TrimSpace(report)
		if reason == "" {
			reason = "agent reached error status"
		}
		return database.Chat{}, "", &subagentStatusError{
			chat:   chat,
			report: report,
			reason: reason,
		}
	}
	return chat, report, nil
}

// subagentGenericErrorMessage matches the normalized fallback that
// chaterror and db2sdk emit for unclassifiable failures. It carries no
// actionable information, so a provider detail replaces it entirely.
const subagentGenericErrorMessage = "The chat request failed unexpectedly."

// subagentLastError decodes a chat's last_error payload and builds the
// message surfaced to the parent model, preferring the actionable
// provider detail. The content mirrors what the chat UI renders from
// the same payload. An unrecognized payload yields an empty message so
// the caller falls back to its own status reason instead of exposing
// raw stored bytes.
func subagentLastError(raw pqtype.NullRawMessage) (*codersdk.ChatError, string) {
	if !raw.Valid {
		return nil, ""
	}
	var payload codersdk.ChatError
	if err := json.Unmarshal(raw.RawMessage, &payload); err != nil {
		return nil, ""
	}
	switch {
	case payload.Message == "" && payload.Detail == "":
		return nil, ""
	case payload.Detail == "":
		return &payload, payload.Message
	case payload.Message == "" || payload.Message == subagentGenericErrorMessage:
		return &payload, payload.Detail
	default:
		return &payload, payload.Message + " (" + payload.Detail + ")"
	}
}

// waitAgentSuccessResponse stops and stores the recording (if active) and
// builds the normal completion payload for a wait_agent call.
func (p *Server) waitAgentSuccessResponse(
	ctx context.Context,
	recordingID string,
	agentConn workspacesdk.AgentConn,
	parent database.Chat,
	targetChat database.Chat,
	report string,
) fantasy.ToolResponse {
	var recResult recordingResult
	if recordingID != "" && agentConn != nil {
		// Use a fresh context for cleanup so a canceled
		// parent context does not prevent recording storage.
		stopCtx, stopCancel := context.WithTimeout(context.WithoutCancel(ctx), subagentRecordingStopTimeout)
		defer stopCancel()
		recResult = p.stopAndStoreRecording(stopCtx, agentConn,
			recordingID, parent.ID, parent.OwnerID, parent.WorkspaceID)
	}
	resp := withSubagentType(map[string]any{
		"chat_id": targetChat.ID.String(),
		"title":   targetChat.Title,
		"report":  report,
		"status":  string(targetChat.Status),
	}, targetChat)
	if recResult.recordingFileID != "" {
		resp["recording_file_id"] = recResult.recordingFileID
	}
	if recResult.thumbnailFileID != "" {
		resp["thumbnail_file_id"] = recResult.thumbnailFileID
	}
	return toolJSONResponse(resp)
}

func (p *Server) interruptSubagent(
	ctx context.Context,
	parentChatID uuid.UUID,
	targetChatID uuid.UUID,
) (database.Chat, bool, error) {
	isDescendant, err := isSubagentDescendant(ctx, p.db, parentChatID, targetChatID)
	if err != nil {
		return database.Chat{}, false, err
	}
	if !isDescendant {
		return database.Chat{}, false, ErrSubagentNotDescendant
	}

	targetChat, err := p.db.GetChatByID(ctx, targetChatID)
	if err != nil {
		return database.Chat{}, false, xerrors.Errorf("get target chat: %w", err)
	}

	if targetChat.Status == database.ChatStatusWaiting {
		return targetChat, false, nil
	}

	updatedChat, err := p.InterruptChat(ctx, targetChat)
	if err != nil {
		// Idle / archived chats no longer satisfy the
		// chatstate.Interrupt precondition. Surface the error
		// so the caller can decide whether the parent expected
		// the subagent to already be waiting.
		return database.Chat{}, false, xerrors.Errorf("interrupt subagent chat: %w", err)
	}
	// chatstate.Interrupt lands active runs in `interrupting`
	// and requires-action chats in `running`. Workers finalize
	// the transition; accept either non-active status as long as
	// the transition committed.
	return updatedChat, true, nil
}

func (p *Server) checkSubagentCompletion(
	ctx context.Context,
	chatID uuid.UUID,
) (database.Chat, string, bool, error) {
	chat, err := p.db.GetChatByID(ctx, chatID)
	if err != nil {
		return database.Chat{}, "", false, xerrors.Errorf("get chat: %w", err)
	}

	// interrupting is transient: the worker transitions it to
	// waiting (no queued messages) or running (queued messages).
	// Treat it as not-done so the agent settles before
	// classification, avoiding stale partial output.
	if chat.Status == database.ChatStatusRunning ||
		chat.Status == database.ChatStatusInterrupting {
		return chat, "", false, nil
	}

	report, err := latestSubagentAssistantMessage(ctx, p.db, chatID)
	if err != nil {
		return database.Chat{}, "", false, err
	}

	return chat, report, true, nil
}

func latestSubagentAssistantMessage(
	ctx context.Context,
	store database.Store,
	chatID uuid.UUID,
) (string, error) {
	messages, err := store.GetChatMessagesByChatID(ctx, database.GetChatMessagesByChatIDParams{
		ChatID:  chatID,
		AfterID: 0,
	})
	if err != nil {
		return "", xerrors.Errorf("get chat messages: %w", err)
	}

	for i := len(messages) - 1; i >= 0; i-- {
		message := messages[i]
		if message.Role != database.ChatMessageRoleAssistant ||
			message.Visibility == database.ChatMessageVisibilityModel {
			continue
		}

		content, parseErr := chatprompt.ParseContent(message)
		if parseErr != nil {
			continue
		}
		text := strings.TrimSpace(contentBlocksToText(content))
		if text == "" {
			continue
		}
		return text, nil
	}

	return "", nil
}

// isSubagentDescendant reports whether targetChatID is a descendant
// of ancestorChatID by walking up the parent chain from the target.
// This is O(depth) DB queries instead of O(nodes) BFS.
func isSubagentDescendant(
	ctx context.Context,
	store database.Store,
	ancestorChatID uuid.UUID,
	targetChatID uuid.UUID,
) (bool, error) {
	if ancestorChatID == targetChatID {
		return false, nil
	}

	currentID := targetChatID
	visited := map[uuid.UUID]struct{}{} // cycle protection
	for {
		if _, seen := visited[currentID]; seen {
			return false, nil
		}
		visited[currentID] = struct{}{}

		chat, err := store.GetChatByID(ctx, currentID)
		if err != nil {
			if xerrors.Is(err, sql.ErrNoRows) {
				return false, nil // chain broken; not a confirmed descendant
			}
			return false, xerrors.Errorf("get chat %s: %w", currentID, err)
		}
		if !chat.ParentChatID.Valid {
			return false, nil // reached root without finding ancestor
		}
		if chat.ParentChatID.UUID == ancestorChatID {
			return true, nil
		}
		currentID = chat.ParentChatID.UUID
	}
}

func subagentFallbackChatTitle(message string) string {
	const maxWords = 6
	const maxRunes = 80

	words := strings.Fields(message)
	if len(words) == 0 {
		return chatprompt.DefaultChatTitle
	}

	truncated := false
	if len(words) > maxWords {
		words = words[:maxWords]
		truncated = true
	}

	title := strings.Join(words, " ")
	if truncated {
		title += "..."
	}

	return subagentTruncateRunes(title, maxRunes)
}

func subagentTruncateRunes(value string, maxRunes int) string {
	if maxRunes <= 0 {
		return ""
	}

	runes := []rune(value)
	if len(runes) <= maxRunes {
		return value
	}

	return string(runes[:maxRunes])
}

func toolJSONResponse(result map[string]any) fantasy.ToolResponse {
	data, err := json.Marshal(result)
	if err != nil {
		return fantasy.NewTextResponse("{}")
	}
	return fantasy.NewTextResponse(string(data))
}

func toolJSONErrorResponse(result map[string]any) fantasy.ToolResponse {
	resp := toolJSONResponse(result)
	resp.IsError = true
	return resp
}