fix: xcecli jobs list -l — hide spurious start line and show pending reason

Three fixes:

1. ExecHosts.UnmarshalJSON: JSON null (sent when no allocation exists)
   was treated as a non-"-" string because json.Unmarshal(null, &str)
   returns nil with str="". This created a phantom HostSlot{NumSlots:1,
   HostName:""} producing "<1*>" for every PEND job. Now null and ""
   are both treated as empty hosts.

2. page_print_jobs.go: added !startTime.IsZero() guard so a zero
   timestamp ("0001-01-01T00:00:00Z") never produces a start line
   even if the status check is bypassed.

3. Added PENDING_REASON field to JobFieldsMap so it is requested from
   the API when -l is passed, and rendered in printJobsVerboseOutput
   for PEND/PSUSP jobs before the start-time section.

src/frontend/xcecli/common/output/page_print_jobs.go

@@ -322,9 +322,20 @@ func printJobsVerboseOutput(jobs *models.JobsResponse, filter []string) {
 		}
 		PrintWrappedLine(w, submitLine, 80, 18)
 
-		// (3) print the start time info
+		// (3) print the pending reason for jobs waiting to be dispatched
+		if job.JobStatus == "PEND" || job.JobStatus == "PSUSP" {
+			if job.PendingReason != "" {
+				fmt.Fprintf(w, " PENDING REASONS:\n")
+				fmt.Fprintf(w, " %s\n", job.PendingReason)
+			}
+		}
+
+		// (4) print the start time info — skip for jobs that haven't started yet
 		startLine := ""
-		if startTime, err := parseJobTime(job.StartTime); err == nil {
+		if job.JobStatus == "PEND" || job.JobStatus == "PSUSP" {
+			goto printEndLine
+		}
+		if startTime, err := parseJobTime(job.StartTime); err == nil && !startTime.IsZero() {
 			month := startTime.Format("Jan")
 			day := startTime.Format("02")
 			exec_hostname := ""
@@ -380,6 +391,7 @@ func printJobsVerboseOutput(jobs *models.JobsResponse, filter []string) {
 		}
 		PrintWrappedLine(w, startLine, 80, 18)
 
+	printEndLine:
 		// (4) print end line
 		endLine := ""
 		if job.JobStatus == "DONE" || job.JobStatus == "EXIT" {

src/frontend/xcecli/models/jobs.go

@@ -32,6 +32,7 @@ const (
 	HEADER_JOB_LAUNCH_TYPE     = "LAUNCH_TYPE"
 	HEADER_JOB_NUM_PROCESSORS  = "NUM_PROCESSORS"
 	HEADER_JOB_INTERACTIVE_URL = "INTERACTIVE_URL"
+	HEADER_JOB_PENDING_REASON  = "PENDING_REASON"
 
 	// second line
 	HEADER_JOB_R15S = "r15s"
@@ -210,6 +211,7 @@ var JobFieldsMap = map[string]string{
 	HEADER_JOB_LAUNCH_TYPE:     "launch_type",
 	HEADER_JOB_NUM_PROCESSORS:  "num_processors",
 	HEADER_JOB_INTERACTIVE_URL: "interactive_job_url",
+	HEADER_JOB_PENDING_REASON:  "pending_reason",
 	//job_filter.HEADER_JOB_PRIORITY:     "job_priority",
 }
 
@@ -258,16 +260,23 @@ func (e ExecHosts) String() string {
 
 // UnmarshalJSON customizes the JSON parsing method, compatible with both string "-" and structure formats
 func (e *ExecHosts) UnmarshalJSON(data []byte) error {
+	// JSON null means no allocation — treat as empty
+	if string(data) == "null" {
+		e.HostSlots = []HostSlot{}
+		e.NumHosts = 0
+		return nil
+	}
+
 	// First try to parse as a string
 	var str string
 	if err := json.Unmarshal(data, &str); err == nil {
-		// If the string is "-", return an empty ExecHosts
-		if str == "-" {
+		// Empty string or "-" both mean no hosts
+		if str == "" || str == "-" {
 			e.HostSlots = []HostSlot{}
 			e.NumHosts = 0
 			return nil
 		}
-		// If it's any other string, treat it as a single hostname
+		// Any other non-empty string is a single hostname
 		e.HostSlots = []HostSlot{{HostName: str, NumSlots: 1}}
 		e.NumHosts = 1
 		return nil