fix(ha-commit-engine): raise commit-barrier default 50->500ms + add --sync-timeout-ms

Live symptom: jobsub intermittently failed with 'Connection timed out' even
though the cluster had quorum. Root cause: the synchronous commit barrier waits
only DEFAULT_SYNC_TIMEOUT_MS=50ms for durable majority replication, and that was
not configurable. 50ms is too tight for durable sync majority replication —
especially since standbys now fdatasync each replicated entry before ACK — so a
multi-entry jobsub's later WAL entry intermittently misses the window:
  commit: WAIT deadline expired without commit (lsn=3 committed_lsn=2 timeout_ms=50)
-> persist hook returns -ETIMEDOUT -> handle_jobsubmit rejects -> client ETIMEDOUT.

Fix:
- Raise DEFAULT_SYNC_TIMEOUT_MS 50 -> 500 (config.h) — realistic for durable sync
  majority replication, still bounded for failure detection.
- Add a --sync-timeout-ms controller flag threaded arguments -> myconf ->
  persist pcfg (override applied before persist_init); 0 = use default, positive
  overrides — so operators can tune per environment.

TDD: literal-pinned persist_config_defaults().sync_timeout_ms == 500. All
timeout-sensitive tests already pass an explicit timeout_ms (none rely on the
default), so none are slowed; full controller suite green under ASAN. No
commit-engine/barrier/replication/wire change beyond the default value + plumbing.
bug-561.

src/controller/main.c

@@ -29,6 +29,7 @@ const char* argp_program_bug_address = BUG_EMAIL;
 #define OPT_CONF_STALE_TIMEOUT 258
 #define OPT_VCPUS              259
 #define OPT_CERTDIR            260
+#define OPT_SYNC_TIMEOUT       261
 
 struct arguments {
     char* myname;
@@ -40,6 +41,7 @@ struct arguments {
     long  conf_stale_timeout;
     int   vcpus;
     char* certdir;
+    uint32_t sync_timeout_ms;
 };
 
 static struct argp_option options[] = {
@@ -58,6 +60,8 @@ static struct argp_option options[] = {
       "Number of virtual CPUs for the task manager (must be >= 1)" },
     { "certdir",            OPT_CERTDIR,  "DIR", 0,
       "Directory containing xce.crt and xce.key (default: <workdir>/certs)" },
+    { "sync-timeout-ms",    OPT_SYNC_TIMEOUT, "MS", 0,
+      "Synchronous majority-replication commit barrier timeout in ms (0 = default)" },
     { 0 }
 };
 
@@ -100,6 +104,13 @@ static error_t parse_opt(int key, char* arg, struct argp_state* state)
     case OPT_CERTDIR:
         arguments->certdir = arg;
         break;
+    case OPT_SYNC_TIMEOUT: {
+        int v = atoi(arg);
+        if (v < 0)
+            argp_error(state, "--sync-timeout-ms must be >= 0 (got: %s)", arg);
+        arguments->sync_timeout_ms = (uint32_t)v;
+        break;
+    }
     default:
         return ARGP_ERR_UNKNOWN;
     }
@@ -151,6 +162,7 @@ int main(int argc, char* argv[])
     arguments.conf_keep_n        = 2;
     arguments.conf_stale_timeout = 86400;
     arguments.vcpus              = 0; /* 0 = not set; use cluster config default */
+    arguments.sync_timeout_ms    = 0; /* 0 = not set; use persist config default */
 
     argp_parse(&argp, argc, argv, 0, 0, &arguments);
 
@@ -199,6 +211,7 @@ int main(int argc, char* argv[])
     myconf.conf_keep_n       = arguments.conf_keep_n;
     myconf.conf_stale_timeout = (time_t)arguments.conf_stale_timeout;
     myconf.vcpus             = arguments.vcpus;
+    myconf.sync_timeout_ms   = arguments.sync_timeout_ms;
     memset(&myconf.peers_cfg, 0, sizeof(myconf.peers_cfg));
 
     if (arguments.peers_str) {