fix: improve state detection accuracy and notification UX

- Hook reads JSON from stdin (not env vars) matching Claude Code protocol
- end_turn = Idle (not NeedsInput); real questions come from hooks
- Permission prompt (stale tool_use) never becomes Idle
- Notifications auto-expire after 10s (--expire-time)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

state.go

@@ -20,34 +20,35 @@ func DetectState(messages []JSONLMessage, now time.Time) SessionState {
 
 	last := messages[len(messages)-1]
 
-	// Check idle threshold first
+	age := time.Duration(0)
 	if ts, err := time.Parse(time.RFC3339, last.Timestamp); err == nil {
-		if now.Sub(ts) > IdleThreshold {
-			return Idle
-		}
+		age = now.Sub(ts)
 	}
 
 	if last.Type == "assistant" && last.Message != nil {
 		switch last.Message.StopReason {
 		case "end_turn":
-			return NeedsInput
+			return Idle
 		case "tool_use":
 			for _, block := range last.Message.Content {
 				if block.Type == "tool_use" && block.Name == "AskUserQuestion" {
 					return NeedsInput
 				}
 			}
-			// If tool_use is stale (no new JSONL activity), Claude is likely
-			// waiting for a permission prompt approval.
-			if ts, err := time.Parse(time.RFC3339, last.Timestamp); err == nil {
-				if now.Sub(ts) > PermissionStallThreshold {
-					return NeedsInput
-				}
+			// Stale tool_use = permission prompt waiting for approval.
+			// Never becomes Idle: a pending permission is always NeedsInput.
+			if age > PermissionStallThreshold {
+				return NeedsInput
 			}
 			return Working
 		}
 	}
 
+	// Non-assistant messages (progress, user): idle if old enough
+	if age > IdleThreshold {
+		return Idle
+	}
+
 	if last.Type == "progress" {
 		return Working
 	}