fix(hitl): keep the diagnosis in the HITL ledger so edited messages retain evidence and rationale

버튼 처리·만료 후 메시지를 편집할 때 빈 진단으로 다시 그려 증거·근거 필드가 "-"로 지워지던
결함을 고친다. ai.hitl_messages에 diagnosis jsonb를 추가해 게시 시점의 진단을 저장하고
편집 시 그대로 재사용한다.

ai/internal/hitl/bot.go

@@ -131,7 +131,7 @@ func (b *Bot) Post(ctx context.Context, req PostRequest) error {
 	if err != nil {
 		return err
 	}
-	if err := b.store.InsertHitl(ctx, rag.HitlMessage{Token: req.Token, ChannelID: msg.ChannelID, MessageID: msg.ID, ActionID: req.ActionID, Target: req.Target, RunID: req.RunID, ScenarioID: req.ScenarioID, SessionID: req.SessionID, ExpiresAt: expires}); err != nil {
+	if err := b.store.InsertHitl(ctx, rag.HitlMessage{Token: req.Token, ChannelID: msg.ChannelID, MessageID: msg.ID, ActionID: req.ActionID, Target: req.Target, Diagnosis: req.Diagnosis, RunID: req.RunID, ScenarioID: req.ScenarioID, SessionID: req.SessionID, ExpiresAt: expires}); err != nil {
 		return err
 	}
 	b.arm(req.Token, time.Until(expires))
@@ -217,14 +217,9 @@ func (b *Bot) Decide(ctx context.Context, token, decision, by string) (string, e
 	return "", fmt.Errorf("unknown decision %s", decision)
 }
 
+// edit re-renders the original message with the stored diagnosis, the new status and disabled buttons.
 func (b *Bot) edit(m *rag.HitlMessage, status string, color int, result map[string]any) error {
-	ctx := context.Background()
-	d := map[string]any{}
-	if se, err := b.store.GetHitl(ctx, m.Token); err == nil {
-		m = se
-	}
-	em := embedFor(d, m.ActionID, m.Target, m.RunID, m.ScenarioID, status, color)
-	em.Fields = em.Fields[1:] // the diagnosis fields are already in the original message; keep the edit compact
+	em := embedFor(m.Diagnosis, m.ActionID, m.Target, m.RunID, m.ScenarioID, status, color)
 	if result != nil {
 		rb, _ := json.Marshal(result)
 		em.Fields = append(em.Fields, &discordgo.MessageEmbedField{Name: "Result", Value: "```json\n" + truncate(string(rb), 900) + "\n```"})