fix: spurious errors/warnings from a pc13v HA deploy (bug-1872..1877)

- bug-1872 (worker): "Failed to find any disk statistics in
  /proc/diskstats" ERROR every 15 s on an NVMe-only host. The whole-disk
  filter guessed from the name and skipped anything ending in a digit or
  containing 'p' -- every nvmeXnY, mmcblkN, even sdp -- so io was never
  reported. diskstats.h now counts a device only when
  /sys/block/<name>/device exists (real disks; not partitions, loop, dm,
  md, zram), and a host with no disk warns once.
- bug-1873 (worker): "Failed to get worker pid" WARN on job start. MainPID
  reads 0 until systemd has forked the new transient unit; xcecd.c already
  retries, so the miss is DEBUG and the final failure names the unit.
- bug-1874 (scheduler): deprecation WARN for the legacy xce_sched_fcfs on
  every start, though builtin_fcfs is the picker. Registration still wraps
  a job_elect_fn plugin but no longer warns; selecting one warns once.
- bug-1875 (apiserver): "Not running as root -- PAM authentication will not
  work" with the default provider config_file; now only for provider pam.
- bug-1876 (controller): standbys logged "cluster_init_phase2 ... failed
  (rc=-22)" WARN every 3 s while waiting for the primary's config push,
  a state the function itself calls normal. It returns -EAGAIN for that
  wait; callers log it at INFO, other failures still WARN.
- bug-1877 (controller): "WAL/snapshot stored unencrypted" warned without
  looking. persist_path_encrypted() checks fscrypt (statx) and dm-crypt
  (sysfs dm/uuid CRYPT-, through LVM slaves); the warning stays when the
  storage is not shown to be encrypted (e.g. a plain /tmp).

Tests: worker diskstats_test (2 of 4 RED on the old filter with pc13v's
/proc/diskstats), controller test_phase2_cold_boot and
test_persist_encryption, scheduler picker tests, apiserver
TestRootWarning. Full ASAN build: all 113 suites pass (controller 319/0,
harness 141/0).

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

src/worker/include/diskstats.h

@@ -0,0 +1,64 @@
+#pragma once
+/*
+ * diskstats.h -- sum the sector counters of the physical disks listed in
+ * /proc/diskstats (node_information.c's io metric).
+ */
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+
+/* A whole physical disk has /sys/block/<name>/device (a link to its
+ * hardware). Partitions are not in /sys/block, and loop, ram, zram, dm-
+ * and md devices have no `device` -- counting dm/md would also count the
+ * same I/O twice, once more through their member disks. */
+static inline int diskstats_is_physical(const char* sysblock, const char* name)
+{
+    char        path[512];
+    struct stat st;
+
+    if (strchr(name, '/') != NULL || name[0] == '.') {
+        return 0;
+    }
+    snprintf(path, sizeof(path), "%s/%s/device", sysblock, name);
+    return stat(path, &st) == 0;
+}
+
+/* Sum sectors read/written over the physical disks in `fp` (a
+ * /proc/diskstats stream). `sysblock` is the /sys/block directory.
+ * Returns the number of disks counted.
+ *
+ * bug-1872: this used to guess from the name (skip names ending in a digit
+ * or containing 'p'), which dropped every NVMe disk (nvme0n1), mmc disks
+ * (mmcblk0) and even sdp. */
+static inline int diskstats_sum_physical(FILE* fp, const char* sysblock,
+                                         unsigned long long* sectors_read,
+                                         unsigned long long* sectors_written)
+{
+    char line[512];
+    int  ndisks = 0;
+
+    *sectors_read    = 0;
+    *sectors_written = 0;
+
+    while (fgets(line, sizeof(line), fp)) {
+        int                major, minor;
+        char               name[64];
+        unsigned long long rc, rm, rd, rt, wc, wm, wr, wt, inprog, iot, wiot;
+
+        if (sscanf(line,
+                   "%d %d %63s %llu %llu %llu %llu %llu %llu %llu %llu %llu "
+                   "%llu %llu",
+                   &major, &minor, name, &rc, &rm, &rd, &rt, &wc, &wm, &wr, &wt,
+                   &inprog, &iot, &wiot)
+            < 14) {
+            continue;
+        }
+        if (!diskstats_is_physical(sysblock, name)) {
+            continue;
+        }
+        *sectors_read += rd;
+        *sectors_written += wr;
+        ndisks++;
+    }
+    return ndisks;
+}