Init commit of jobs output/error message peek project.

src/frontend/apiserver/backend/clib.go

@@ -416,3 +416,41 @@ func signalNumber(signame string, action int) int {
 	}
 	return 15 // SIGTERM as safe default
 }
+
+// FetchFile fetches up to maxBytes of a job output file from offset via the
+// controller→worker chain. The filepath must be the fully resolved absolute
+// path on the exec host.
+func FetchFile(jobid uint64, filepath string, offset uint64, maxBytes uint32) (*FetchFileResult, error) {
+cFilepath := C.CString(filepath)
+defer C.free(unsafe.Pointer(cFilepath))
+
+msg := C.xce_fetchfile_t{
+jobid:     C.uint64_t(jobid),
+filepath:  cFilepath,
+offset:    C.uint64_t(offset),
+max_bytes: C.uint32_t(maxBytes),
+}
+
+var reply *C.xce_fetchfile_reply_t
+rc := C.xcecli_fetchfile(gCtx.ctx, &msg, &reply)
+if rc < 0 {
+return nil, fmt.Errorf("xcecli_fetchfile failed: %d", int(rc))
+}
+if reply == nil {
+return nil, fmt.Errorf("xcecli_fetchfile returned nil reply")
+}
+defer C.free(unsafe.Pointer(reply))
+
+if reply.error != 0 {
+return nil, fmt.Errorf("fetchfile remote error: %d", int(reply.error))
+}
+
+result := &FetchFileResult{
+FileSize:  uint64(reply.file_size),
+BytesRead: uint32(reply.bytes_read),
+}
+if reply.bytes_read > 0 && reply.content != nil {
+result.Content = C.GoBytes(unsafe.Pointer(reply.content), C.int(reply.bytes_read))
+}
+return result, nil
+}

src/frontend/apiserver/backend/config.go

@@ -8,3 +8,10 @@ type BackendConfig struct {
 	From    string // identity sent to controller (default: "xce_apiserver")
 	Key     string // authentication key
 }
+
+// FetchFileResult holds the data returned by FetchFile.
+type FetchFileResult struct {
+	Content   []byte
+	FileSize  uint64
+	BytesRead uint32
+}

src/frontend/apiserver/backend/convert_pure.go

@@ -3,6 +3,7 @@ package backend
 import (
 	"apiserver/models"
 	"encoding/json"
+	"fmt"
 	"time"
 )
 
@@ -76,6 +77,33 @@ func IsArrayJob(id uint64) bool {
 	return extractIDTag(id) == tagJobArray
 }
 
+// FormatJobID formats a packed 64-bit job ID as a human-readable string,
+// matching the C fmt_jobid() output in src/lib/utils.c.
+//   - Regular job:  "{cluster}-{apiserver}-{timestamp}-{sequence}"
+//   - Array child:  "{cluster}-{apiserver}-{timestamp}-{base}[{idx}]"
+func FormatJobID(uniqueJobID int64) string {
+	id := uint64(uniqueJobID)
+	clusterID := extractBits(id, clusterIDShift, nClusterIDBits)
+	apiserverID := extractBits(id, apiserverIDShift, nApiserverIDBits)
+	timestamp := extractBits(id, timestampShift, nTimestampBits)
+
+	if extractIDTag(id) == tagJobArray {
+		arrayBase := extractBits(id, sequenceHighShift, nSequenceBits-nArrayIdxBits) << uint(sequenceHighShift)
+		arrayIdx := extractBits(id, 0, nArrayIdxBits)
+		return fmt.Sprintf("%d-%d-%d-%d[%d]",
+			clusterID, apiserverID, timestamp, arrayBase, arrayIdx)
+	}
+	sequence := extractBits(id, 0, nSequenceBits)
+	return fmt.Sprintf("%d-%d-%d-%d",
+		clusterID, apiserverID, timestamp, sequence)
+}
+
+// WorkerDefaultOutputPath returns the output file path the worker uses by default
+// for the given job ID and task index, matching uv_proc.c make_job_output_path().
+func WorkerDefaultOutputPath(uniqueJobID int64, taskIdx int) string {
+	return fmt.Sprintf("/tmp/job_%s_task%d.out", FormatJobID(uniqueJobID), taskIdx)
+}
+
 // rawStartInfo mirrors the C job_startinfo_t fields used by the Go model.
 type rawStartInfo struct {
 	cmdline    string

src/frontend/apiserver/backend/stub.go

@@ -41,3 +41,8 @@ func EvalSelectForHost(_, _ string) error { return errNoCGO }
 
 // Cleanup stub — real implementation in clib.go (requires CGO).
 func Cleanup() {}
+
+// FetchFile stub — real implementation in clib.go (requires CGO).
+func FetchFile(_ uint64, _ string, _ uint64, _ uint32) (*FetchFileResult, error) {
+	return nil, errNoCGO
+}