test(e2e): entrypoint ERR trap and richer CI failure logs

CI showed exit=1 in ~3s with empty docker logs after /data/opendkim was
created. Log each entrypoint step and trap ERR with LINENO; also read the
container LogPath and docker logs by container id when compose logs are empty.

Co-Authored-By: Composer <noreply@cursor.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

test/e2e/hostname_gate_test.go

@@ -128,6 +128,21 @@ func runEntrypointBackground(t *testing.T, hostnameEnv string) (output string, s
 	inspect, _ := exec.Command("docker", "inspect", name, "--format",
 		"status={{.State.Status}} exit={{.State.ExitCode}} err={{.State.Error}} oom={{.State.OOMKilled}} started={{.State.StartedAt}} finished={{.State.FinishedAt}}").CombinedOutput()
 	logs, logErr := exec.Command("docker", "logs", name).CombinedOutput()
+	// Exited containers sometimes yield empty `docker logs` in CI; also read
+	// the JSON-file log path docker recorded on the container.
+	logPathOut, _ := exec.Command("docker", "inspect", name, "--format", "{{.LogPath}}").CombinedOutput()
+	logPath := strings.TrimSpace(string(logPathOut))
+	logFileHead := ""
+	if logPath != "" {
+		if b, e := os.ReadFile(logPath); e == nil {
+			logFileHead = truncateForDebug(string(b), 4000)
+			if strings.TrimSpace(string(logs)) == "" && len(b) > 0 {
+				logs = b
+			}
+		} else {
+			logFileHead = "read LogPath: " + e.Error()
+		}
+	}
 	dataMode, _ := exec.Command("docker", "exec", name, "stat", "-c", "%a %U:%G", "/data").CombinedOutput()
 	opendkimStat, _ := exec.Command("docker", "exec", name, "stat", "-c", "%a %U:%G", "/data/opendkim").CombinedOutput()
 	keyTableStat, _ := exec.Command("docker", "exec", name, "stat", "-c", "%a %U:%G", "/data/opendkim/KeyTable").CombinedOutput()
@@ -147,16 +162,18 @@ func runEntrypointBackground(t *testing.T, hostnameEnv string) (output string, s
 		hostDataListing = strings.Join(parts, ",")
 	}
 	agentDebugLog("H1", "hostname_gate_test.go:post-wait", "data permissions", map[string]any{
-		"dataMode":      strings.TrimSpace(string(dataMode)),
-		"opendkimStat":  strings.TrimSpace(string(opendkimStat)),
-		"keyTableStat":  strings.TrimSpace(string(keyTableStat)),
+		"dataMode":        strings.TrimSpace(string(dataMode)),
+		"opendkimStat":    strings.TrimSpace(string(opendkimStat)),
+		"keyTableStat":    strings.TrimSpace(string(keyTableStat)),
 		"hostDataListing": hostDataListing,
 	})
 	agentDebugLog("H2", "hostname_gate_test.go:post-wait", "container inspect", map[string]any{
-		"inspect": strings.TrimSpace(string(inspect)),
-		"waitErr": fmt.Sprintf("%v", err),
-		"logErr":  fmt.Sprintf("%v", logErr),
-		"logLen":  len(logs),
+		"inspect":    strings.TrimSpace(string(inspect)),
+		"waitErr":    fmt.Sprintf("%v", err),
+		"logErr":     fmt.Sprintf("%v", logErr),
+		"logLen":     len(logs),
+		"logPath":    logPath,
+		"logFileHead": logFileHead,
 	})
 	agentDebugLog("H3", "hostname_gate_test.go:post-wait", "supervisor and logs", map[string]any{
 		"supervisorctl": strings.TrimSpace(string(supStatus)),
@@ -167,8 +184,11 @@ func runEntrypointBackground(t *testing.T, hostnameEnv string) (output string, s
 	diag := string(logs)
 	if strings.TrimSpace(diag) == "" {
 		diag = "(empty docker logs)\ninspect: " + strings.TrimSpace(string(inspect)) +
+			"\nlogPath: " + logPath +
+			"\nlogFileHead: " + logFileHead +
 			"\nsupervisorctl: " + strings.TrimSpace(string(supStatus)) +
-			"\n/data mode: " + strings.TrimSpace(string(dataMode))
+			"\n/data mode: " + strings.TrimSpace(string(dataMode)) +
+			"\nhost /data: " + hostDataListing
 	}
 	return diag, err == nil
 }