fix: handle zero values in cron schedule type assertions (#1147)

Fixes #1126

Go type assertions return true for zero values, which caused recurring
cron jobs (every_seconds/cron_expr) to silently become one-time 'at' tasks
when LLMs filled unused optional parameters with default values (0).

Changes:
- Add validity checks after type assertions: atSeconds > 0, everySeconds > 0, cronExpr != ""
- This ensures zero values are treated as 'not set' rather than valid schedule values
- Recurring tasks like "remind me every 2 hours" now correctly create recurring jobs

pkg/tools/cron.go

@@ -141,6 +141,12 @@ func (t *CronTool) addJob(ctx context.Context, args map[string]any) *ToolResult
 	everySeconds, hasEvery := args["every_seconds"].(float64)
 	cronExpr, hasCron := args["cron_expr"].(string)
 
+	// Fix: type assertions return true for zero values, need additional validity checks
+	// This prevents LLMs that fill unused optional parameters with defaults (0) from triggering wrong type
+	hasAt = hasAt && atSeconds > 0
+	hasEvery = hasEvery && everySeconds > 0
+	hasCron = hasCron && cronExpr != ""
+
 	// Priority: at_seconds > every_seconds > cron_expr
 	if hasAt {
 		atMS := time.Now().UnixMilli() + int64(atSeconds)*1000