sweep: dedup session->Turn conversion, fix drifted line reference (V-581)

chatHistory (voice.go) and rememberTurn (clarify.go) both built the same
dialogue.Turn{Intent, Slots, Text} projection of a *dialogue.Session
inline; factor it into sessionAsTurn and use it in both. Also name the
history-depth cap (previously a bare "3") as maxCarriedHistory, and fix
chatHistory's doc comment, which cited "lines 373-395" for the dialogue
merge in runTurn -- that block has since moved to lines 385-394. Point
at the step-6 comment instead of a line range so the reference survives
future edits. No behavior change; bookkeeping only, not the clarify/
reminder slot-decision logic.

cmd/mavend/clarify.go

@@ -527,20 +527,22 @@ func (h *reactiveHandler) finishClarified(ctx context.Context, dec router.Decisi
 	return reply
 }
 
+// maxCarriedHistory — how many turns of PRIOR history (beyond the immediate
+// last turn) rememberTurn carries forward. The session ends up holding this
+// many plus the one just-finished turn, so callers describing the total
+// depth (chatHistory's doc comment, this one) say "up to 4".
+const maxCarriedHistory = 3
+
 // rememberTurn stores this turn as the dialogue session the next follow-up
 // inherits from, carrying up to 4 prior turns of history for anaphora. Capped so
 // one long conversation can't grow the session unboundedly.
 func (h *reactiveHandler) rememberTurn(ctx context.Context, prev *dialogue.Session, dec router.Decision, now time.Time) {
 	var history []dialogue.Turn
 	if prev != nil {
-		history = append(history, dialogue.Turn{
-			Intent: prev.Intent,
-			Slots:  prev.Slots,
-			Text:   prev.Slots.Text,
-		})
+		history = append(history, sessionAsTurn(prev))
 		maxHist := len(prev.History)
-		if maxHist > 3 {
-			maxHist = 3
+		if maxHist > maxCarriedHistory {
+			maxHist = maxCarriedHistory
 		}
 		history = append(history, prev.History[:maxHist]...)
 	}

cmd/mavend/voice.go

@@ -528,6 +528,17 @@ func (h *reactiveHandler) replySystem(ctx context.Context, dec router.Decision)
 	}
 }
 
+// sessionAsTurn projects a stored session onto the dialogue.Turn shape used in
+// history lists. Shared by chatHistory and rememberTurn (clarify.go) so the
+// same session is described the same way in both places.
+func sessionAsTurn(s *dialogue.Session) dialogue.Turn {
+	return dialogue.Turn{
+		Intent: s.Intent,
+		Slots:  s.Slots,
+		Text:   s.Slots.Text,
+	}
+}
+
 // chatHistory collects dialogue turns from the session store for the current
 // conversation. Returns prior user utterances (newest last) up to a depth of
 // 4 turns. Returns nil when there's no session or no history.
@@ -541,13 +552,9 @@ func (h *reactiveHandler) chatHistory(ctx context.Context) []dialogue.Turn {
 		return nil
 	}
 	// History already includes the immediate prior turn (set by the dialogue
-	// merge at lines 373-395), plus up to 3 more from deeper history.
+	// merge in runTurn's step 6, above), plus up to 3 more from deeper history.
 	out := make([]dialogue.Turn, 0, 1+len(prev.History))
-	out = append(out, dialogue.Turn{
-		Intent: prev.Intent,
-		Slots:  prev.Slots,
-		Text:   prev.Slots.Text,
-	})
+	out = append(out, sessionAsTurn(prev))
 	out = append(out, prev.History...)
 	return out
 }