diff --git a/.doc/system-design/module-boundaries.yaml b/.doc/system-design/module-boundaries.yaml
index c3711a3d..1c86a2c7 100644
--- a/.doc/system-design/module-boundaries.yaml
+++ b/.doc/system-design/module-boundaries.yaml
@@ -259,6 +259,7 @@ imports:
     - workflowdef
     - workflowscope
     - workspace
+    - supplementimpact
   squad:
     - agent
     - config
diff --git a/internal/supplementimpact/http_adapter.go b/internal/supplementimpact/http_adapter.go
index b34e7d38..39138b55 100644
--- a/internal/supplementimpact/http_adapter.go
+++ b/internal/supplementimpact/http_adapter.go
@@ -3,6 +3,7 @@ package supplementimpact
 import (
 	"context"
 	"fmt"
+	"time"
 )
 
 // HTTPBatchView is the JSON shape expected by server supplement-impact handlers.
@@ -18,7 +19,7 @@ type HTTPBatchView struct {
 	DecisionNonce   string          `json:"decision_nonce"`
 	DecisionDigest  string          `json:"decision_digest,omitempty"`
 	Revision        int64           `json:"revision"`
-	ExpiresAt       interface{}     `json:"expires_at"`
+	ExpiresAt       time.Time       `json:"expires_at"`
 	Items           []HTTPItemView  `json:"items,omitempty"`
 }