fix: handle agent not found (#951)

Co-authored-by: Copilot <[email protected]>

Author: mattjohnsonpint

CHANGELOG.md

@@ -11,6 +11,7 @@ NOTE: all releases may include dependency updates, not specifically mentioned
 ## 2025-07-14 - Runtime v0.18.6
 
 - feat: restore agents on demand [#949](https://github.com/hypermodeinc/modus/pull/949)
+- fix: handle agent not found [#951](https://github.com/hypermodeinc/modus/pull/951)
 
 ## 2025-07-12 - Runtime v0.18.5
 

runtime/actors/agents.go

@@ -224,12 +224,11 @@ func SendAgentMessage(ctx context.Context, agentId string, msgName string, data
 
 		if errors.Is(err, goakt.ErrActorNotFound) {
 			state, err := db.GetAgentState(ctx, agentId)
-			if err != nil {
+			if errors.Is(err, db.ErrAgentNotFound) {
+				return newAgentMessageErrorResponse(fmt.Sprintf("agent %s not found", agentId)), nil
+			} else if err != nil {
 				return nil, fmt.Errorf("error getting agent state for %s: %w", agentId, err)
 			}
-			if state == nil {
-				return newAgentMessageErrorResponse("agent not found"), nil
-			}
 
 			switch AgentStatus(state.Status) {
 			case AgentStatusStopping, AgentStatusTerminated:

runtime/db/agentstate.go

@@ -7,16 +7,20 @@ package db
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"time"
 
 	"github.com/hypermodeinc/modus/runtime/sentryutils"
 	"github.com/hypermodeinc/modus/runtime/utils"
 
 	"github.com/hypermodeinc/modusgraph"
+	mg_utils "github.com/hypermodeinc/modusgraph/api/apiutils"
 	"github.com/jackc/pgx/v5"
 )
 
+var ErrAgentNotFound = errors.New("agent not found")
+
 type AgentState struct {
 	Gid       uint64 `json:"gid,omitempty"`
 	Id        string `json:"id" db:"constraint=unique"`
@@ -93,6 +97,10 @@ func getAgentStateFromModusDB(ctx context.Context, id string) (*AgentState, erro
 		Key:   "id",
 		Value: id,
 	})
+	if errors.Is(err, mg_utils.ErrNoObjFound) {
+		return nil, ErrAgentNotFound
+	}
+
 	if err != nil {
 		return nil, fmt.Errorf("failed to query agent state: %w", err)
 	}
@@ -174,6 +182,9 @@ func getAgentStateFromPostgresDB(ctx context.Context, id string) (*AgentState, e
 	err := WithTx(ctx, func(tx pgx.Tx) error {
 		row := tx.QueryRow(ctx, query, id)
 		if err := row.Scan(&a.Id, &a.Name, &a.Status, &a.Data, &ts); err != nil {
+			if errors.Is(err, pgx.ErrNoRows) {
+				return ErrAgentNotFound
+			}
 			return fmt.Errorf("failed to get agent state: %w", err)
 		}
 		a.UpdatedAt = ts.UTC().Format(utils.TimeFormat)