fix(apiserver): reject a malformed rusage[] at job submit (bug-1744)

Gitea #47: `xcecli jobs submit -R "rusage[mem=100000000a0]"` was accepted
with a normal "Job <...> is submitted" reply. The apiserver only
length-checked resreq; the real PEG grammar ran later, asynchronously, in
the scheduler's core_build_job(), which logged a server-side WARN and
dropped the job -- it then sat PEND forever with no sign of why.

- libxce: xce_check_rusage_syntax(resreq, &errmsg) runs parse_rusage() on
  every rusage[...] clause (extracted the way section.peg does: up to the
  first ']'), so primary, compound and alternative requests are all
  covered. No resource manager needed, so select[]/order[] resource names
  are still only checked by the scheduler (the documented scope).
- apiserver/backend: ValidateResreqSyntax() cgo wrapper (resreq_check.go);
  the !cgo stub returns nil (no job can be submitted without CGO anyway).
- controllers/jobs.go preCheckJobRequest(): calls it after the length
  check via a package var, so a malformed request is refused up front.

Tests: lib test_check_rusage_syntax (RED before: the reported input was
accepted) and backend TestValidateResreqSyntax (RED before) through the
real grammar; controllers TestPreCheckJobRequest_RejectsMalformedResreq
checks the call site with an injected validator (written with the call
site, so no separate RED). libxce, apiserver backend (cgo) and controllers
tests pass. apiserver/middleware TestLoadJobs fails here and on the
baseline alike: it needs a live apiserver on :8080.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/frontend/apiserver/controllers/jobs.go

@@ -1530,6 +1530,10 @@ func preCheckJobRestartRequest(req *models.JobRestartRequest) error {
 	return nil
 }
 
+// validateResreqSyntax is the resource-request syntax check used by
+// preCheckJobRequest; a variable so tests can substitute it (bug-1744).
+var validateResreqSyntax = backend.ValidateResreqSyntax
+
 func preCheckJobRequest(req *models.JobSubmitRequest) ([]int, error) {
 	logger.Debug("Enter preCheckJobRequest")
 	if req.QueueName == "" {
@@ -1603,6 +1607,11 @@ func preCheckJobRequest(req *models.JobSubmitRequest) ([]int, error) {
 		if len(req.Resreq) > 4094 {
 			return nil, errors.New("resreq length exceeds the limit of 4094 characters")
 		}
+		// bug-1744: reject a malformed rusage[] clause now, instead of
+		// accepting the job and letting the scheduler silently drop it.
+		if err := validateResreqSyntax(req.Resreq); err != nil {
+			return nil, err
+		}
 	}
 
 	if req.ShellLimit.CPULimit != 0 {

src/frontend/apiserver/controllers/jobs_test.go

@@ -1,6 +1,7 @@
 package controllers
 
 import (
+	"errors"
 	"apiserver/models"
 	"apiserver/store"
 	"apiserver/utils"
@@ -192,3 +193,32 @@ func TestFoundJob_MatchesRealArrayIdxType(t *testing.T) {
 		t.Fatalf("expected to find 1 job, got %d", len(found))
 	}
 }
+
+// TestPreCheckJobRequest_RejectsMalformedResreq (bug-1744): a resource request
+// the syntax check rejects must fail the submission instead of being accepted
+// and later silently dropped by the scheduler.
+func TestPreCheckJobRequest_RejectsMalformedResreq(t *testing.T) {
+	resetJobSubmitState()
+	store.Queues.Put("normal", models.QueueInfo{QueueName: "normal"})
+
+	var checked string
+	orig := validateResreqSyntax
+	validateResreqSyntax = func(s string) error {
+		checked = s
+		if strings.Contains(s, "100000000a0") {
+			return errors.New("invalid rusage in resource request")
+		}
+		return nil
+	}
+	defer func() { validateResreqSyntax = orig }()
+
+	req := &models.JobSubmitRequest{QueueName: "normal",
+		Resreq: "rusage[mem=100000000a0]"}
+	_, err := preCheckJobRequest(req)
+	if checked != "rusage[mem=100000000a0]" {
+		t.Fatalf("resreq was not syntax-checked (checked %q)", checked)
+	}
+	if err == nil || !strings.Contains(err.Error(), "invalid rusage") {
+		t.Fatalf("malformed resreq must be rejected, got err=%v", err)
+	}
+}