feat: add --peers to controller for HA peer list and priority election

- myconf_t gains peers_cfg (xce_cluster_config_t) populated from --peers
- controller/main.c: parse --peers host:port,... via argp; ca_cert_path
  auto-derived from workdir/certs/xce.crt (no --ca-cert flag needed)
- cluster_init: derive my_priority from position in peers list (index 0 =
  primary); fall back to 0 when --peers not given (single-node mode)

docs/superpowers/plans/2026-05-07-persistence-ha-overview.md

@@ -0,0 +1,39 @@
+# XCE Persistence & HA — Implementation Overview
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Make the XCE controller survive restarts and primary failures with no job/worker/queue state loss.
+
+**Architecture:** WAL + periodic checkpoint (dual-zarray COW) for single-controller persistence; LSF-style priority election + fan-out TCP replication for HA. libxce smart discovery handles client auto-reconnect after failover.
+
+**Tech Stack:** C (controller/lib), Cap'n Proto (serialization), Nix flakes + meson + ninja (build), Go (API server discovery bridge)
+
+---
+
+## Phase Map
+
+Each phase is an independently shippable increment. Create the next phase plan only after the current phase passes its gate tests.
+
+| Phase | Plan file | Goal | Gate |
+|-------|-----------|------|------|
+| **P0** | `2026-05-07-p0-single-controller-persistence.md` | Controller survives restart | `P0-G` smoke tests green |
+| **P1** | _create after P0 ships_ | Standby takes over when primary fails | Election + promotion tests green |
+| **P2** | _create after P1 ships_ | Primary replicates to standbys in real time | Replication round-trip + catch-up tests green |
+| **P2.5** | _create alongside P2_ | Workers/schedulers auto-reconnect after failover | Discovery + reconnect tests green |
+| **P3** | _create after P2 ships_ | End-to-end failover + hardening + metrics | Full failover test + benchmark passing |
+| **P4** | _create after P3 ships_ | Docs, runbook, stale-ref cleanup | Runbook review complete |
+
+## Out of Scope (all phases)
+
+- Admin CLI for manual failover (`xce hostcontrol --failover`)
+- WAL compaction beyond checkpoint trimming
+- Multi-DC replication
+- Runtime config changes without restart
+- Snapshot compression
+- `config_version` hash in heartbeat (deferred to P3 tooling)
+- Degraded-mode restricted-state timeout (`repl_degraded_timeout_s`)
+- `MAX_HA_CANDIDATES > 4` / `MAX_STANDBYS > 3`
+
+## Design Document
+
+`src/docs/persistence-and-ha-design.md` — all implementation detail lives here. Read the relevant Part before starting each task.

src/controller/cluster.c

@@ -640,8 +640,28 @@ int cluster_init(cluster_t* c)
             .probe_connect_timeout_ms = HA_DEFAULT_PROBE_CONNECT_TIMEOUT_MS,
             .max_promotion_retries    = HA_DEFAULT_MAX_PROMOTION_RETRIES,
         };
-        /* my_priority: single-node P1 always uses 0 (highest priority) */
+
-        rc = ha_init(&c->ha, &ha_cfg, 0);
+        /* Derive priority from position in --peers list.
+         * Index 0 = highest priority (becomes primary on startup).
+         * If the controller's name is not found in the list, fall back to
+         * the last index (lowest priority = standby). */
+        int my_priority = 0;
+        const xce_cluster_config_t* pcfg = &c->myconf->peers_cfg;
+        if (pcfg->candidates_count > 0) {
+            my_priority = pcfg->candidates_count - 1; /* default: last = lowest */
+            for (int i = 0; i < pcfg->candidates_count; i++) {
+                if (strncmp(pcfg->candidates[i].hostname,
+                            c->myconf->name,
+                            XCE_MAXHOSTNAME_LEN - 1) == 0) {
+                    my_priority = i;
+                    break;
+                }
+            }
+            INFO("HA peers: %d candidates, my_priority=%d (name=%s)",
+                 pcfg->candidates_count, my_priority, c->myconf->name);
+        }
+
+        rc = ha_init(&c->ha, &ha_cfg, my_priority);
         if (rc != 0) {
             ERROR("ha_init failed: %d", rc);
             persist_fini(&c->persist);

src/controller/main.c

@@ -6,6 +6,7 @@
 
 #include "myconf.h"
 #include "utils.h"
+#include "xce/cluster.h"
 
 extern int myapp_run(myconf_t*);
 
@@ -15,11 +16,15 @@ const char* argp_program_version
     = MK_VERSION("xce v0.0.1-", STR(VERSION_COMMIT_ID));
 const char* argp_program_bug_address = BUG_EMAIL;
 
+/* Long-option key (above ASCII to avoid collisions with short opts) */
+#define OPT_PEERS 256
+
 struct arguments {
     char* myname;
     char* logfile;
     char* workdir;
     int   verbose;
+    char* peers_str;
 };
 
 static struct argp_option options[] = {
@@ -27,9 +32,44 @@ static struct argp_option options[] = {
     { "logfile", 'l', "FILE",  0, "The full path of log file" },
     { "verbose", 'v', 0,       0, "Produce verbose logs" },
     { "myname",  'n', "STR",   0, "The name of controller" },
+    { "peers",   OPT_PEERS, "PEERS", 0,
+      "HA peer list: comma-separated host:port pairs ordered by priority "
+      "(e.g. ctrl01:9990,ctrl02:9990). Index 0 = highest priority (primary)." },
     { 0 }
 };
 
+/* parse_peers — split "host:port,host:port,..." into cfg->candidates[].
+ * Accepts optional "name=host:port" prefix (name is ignored for controller).
+ * Returns 0 on success, -1 on empty input or parse error. */
+static int parse_peers(const char* peers_str, xce_cluster_config_t* cfg)
+{
+    cfg->candidates_count = 0;
+    if (!peers_str || peers_str[0] == '\0')
+        return -1;
+
+    char buf[2048];
+    strncpy(buf, peers_str, sizeof(buf) - 1);
+    buf[sizeof(buf) - 1] = '\0';
+
+    char* saveptr;
+    char* tok = strtok_r(buf, ",", &saveptr);
+    while (tok && cfg->candidates_count < MAX_HA_CANDIDATES) {
+        char* eq    = strchr(tok, '=');
+        char* addr  = eq ? eq + 1 : tok;
+        char* colon = strrchr(addr, ':');
+        if (!colon)
+            return -1;
+        *colon = '\0';
+        strncpy(cfg->candidates[cfg->candidates_count].hostname, addr,
+                XCE_MAXHOSTNAME_LEN - 1);
+        cfg->candidates[cfg->candidates_count].hostname[XCE_MAXHOSTNAME_LEN - 1] = '\0';
+        cfg->candidates[cfg->candidates_count].port = atoi(colon + 1);
+        cfg->candidates_count++;
+        tok = strtok_r(NULL, ",", &saveptr);
+    }
+    return cfg->candidates_count > 0 ? 0 : -1;
+}
+
 static error_t parse_opt(int key, char* arg, struct argp_state* state)
 {
     struct arguments* arguments = state->input;
@@ -47,6 +87,9 @@ static error_t parse_opt(int key, char* arg, struct argp_state* state)
     case 'n':
         arguments->myname = arg;
         break;
+    case OPT_PEERS:
+        arguments->peers_str = arg;
+        break;
     default:
         return ARGP_ERR_UNKNOWN;
     }
@@ -111,6 +154,27 @@ int main(int argc, char* argv[])
     myconf.keyfile        = key_file;
     myconf.workdir        = arguments.workdir;
     myconf.name           = arguments.myname;
+    memset(&myconf.peers_cfg, 0, sizeof(myconf.peers_cfg));
+
+    if (arguments.peers_str) {
+        if (parse_peers(arguments.peers_str, &myconf.peers_cfg) != 0) {
+            fprintf(stderr,
+                    "xce_controller: --peers parse error: expected "
+                    "host:port,... got: %s\n",
+                    arguments.peers_str);
+            return 1;
+        }
+        /* CA cert derived from workdir — same infrastructure as certfile/keyfile */
+        snprintf(myconf.peers_cfg.ca_cert_path,
+                 sizeof(myconf.peers_cfg.ca_cert_path),
+                 "%s/certs/xce.crt", arguments.workdir);
+        strncpy(myconf.peers_cfg.identity, arguments.myname,
+                sizeof(myconf.peers_cfg.identity) - 1);
+        INFO("HA mode: %d controller candidates, identity=%s",
+             myconf.peers_cfg.candidates_count, myconf.peers_cfg.identity);
+    } else {
+        INFO("No --peers flag; running as single-node primary");
+    }
 
     myapp_run(&myconf);
 

src/include/myconf.h

@@ -7,6 +7,7 @@
 #include <tlog.h>
 
 #include "clusterconfig.h"
+#include "xce/cluster.h"
 
 struct logging {
     char* logdir;
@@ -20,6 +21,7 @@ typedef struct {
     char*                keyfile;
     char*                workdir;    /* working directory for WAL/snapshot storage */
     char*                name;       /* controller name (hostname by default) */
+    xce_cluster_config_t peers_cfg;  /* HA peer list parsed from --peers; count==0 = single-node */
 } myconf_t;
 
 extern cluster_config_t* get_default_conf(void*);