fix(apiserver): send exdata, exec cwd and exec home with submitted jobs (bug-1936)

Cause: modelJobToSubmit() filled only cmdline, execuser, launch_type and
pre/post-exec of job_startinfo_t, so the extended data the submit handler
builds (env, *_limit incl. -W run limit, file transfers, interactive mode),
the cwd and the exec home never reached the controller or the worker.

Fix: map the start info in a pure submitStartInfo() (exdata from
ExtendData, execcwd from ExecCWD or CWD, exechome from ExecHome) that
modelJobToSubmit copies into the C struct; decode exdata back in
cJobToModel/cJobArrayToModels so the store keeps ExtendData and CWD.
Reject extend_data the worker's parse_exdata() cannot take (not a JSON
object, over EXDATA_LENGTH-1 bytes) and drop an empty transfer list
instead of sending a null.

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

src/frontend/apiserver/backend/convert_pure.go

@@ -236,6 +236,55 @@ type rawStartInfo struct {
 	execHome   string
 	execCWD    string
 	execUser   string
+	exdata     string
+}
+
+// submitStartInfo maps a Go JobInfo to the job_startinfo_t fields a
+// submission carries to the controller (and from there, unchanged, to the
+// worker's startjob request). modelJobToSubmit (convert.go) is the CGO
+// adapter that copies the result into the C struct.
+//
+// bug-1936: exdata (env, limits, transfers, interactive mode, built by the
+// submit handler into ExtendData), the exec cwd and the exec home were
+// never set, so none of them reached the worker.
+func submitStartInfo(job *models.JobInfo) rawStartInfo {
+	execCWD := job.ExecCWD
+	if execCWD == "" {
+		execCWD = job.CWD
+	}
+	return rawStartInfo{
+		cmdline:    job.Command,
+		launchType: job.LaunchType,
+		preExec:    job.PreExecCmd,
+		postExec:   job.PostExecCmd,
+		execHome:   job.ExecHome,
+		execCWD:    execCWD,
+		execUser:   resolveExecUser(job.ExecUser, job.SubmitUser),
+		exdata:     job.ExtendData.String,
+	}
+}
+
+// maxExdataLen is the longest exdata the worker can take: xcecd hands it to
+// xcecd_worker in job_assignment_t.exdata[EXDATA_LENGTH] (16 KiB,
+// src/worker/include/uv_ipc.h), NUL included.
+const maxExdataLen = 16*1024 - 1
+
+// ValidateExdata checks a job's extended data before it is submitted: the
+// worker's parse_exdata() fails the job at launch on anything but a JSON
+// object, and a longer string than maxExdataLen would be cut short on its
+// way to the job process.
+func ValidateExdata(exdata string) error {
+	if exdata == "" {
+		return nil
+	}
+	if len(exdata) > maxExdataLen {
+		return fmt.Errorf("extended job data is %d bytes, more than the limit of %d", len(exdata), maxExdataLen)
+	}
+	var obj map[string]interface{}
+	if err := json.Unmarshal([]byte(exdata), &obj); err != nil {
+		return errors.New("extended job data must be a JSON object")
+	}
+	return nil
 }
 
 // rawSubmitData mirrors the C job_submit_data_t fields used by the Go model.
@@ -358,7 +407,9 @@ func rawJobToModel(r rawJobData) *models.JobInfo {
 			info.PostExecCmd = si.postExec
 			info.ExecHome = si.execHome
 			info.ExecCWD = si.execCWD
+			info.CWD = si.execCWD // the submit cwd is sent as the exec cwd (bug-1936)
 			info.ExecUser = si.execUser
+			info.ExtendData = models.Jsonb{String: si.exdata}
 		}
 	}
 	info.SubmitTime = r.subTime