feat(ha-term-safety): add WAL_CONFIG_MARKER entry type + reference payload codec (task 4.1)

src/controller/config_repl.c

@@ -37,6 +37,57 @@
 #include "xce/cluster_def.h"
 #include "wal_types.h"         /* wal_entry_hdr_t, WAL_* constants */
 
+/* ── WAL_CONFIG_MARKER codec (ha-term-safety task 4.1) ───────────────
+ * Fixed, padding-independent serialization of a config-change marker:
+ * 8-byte big-endian version_tag followed by the raw 32-byte SHA-256. NO
+ * configuration bytes are ever encoded (R7.2/R7.4) — the bytes travel
+ * out-of-band on the config-push transport. The explicit byte layout (rather
+ * than a struct memcpy) keeps the form stable across compiler padding and host
+ * endianness, since this payload replicates to standbys via AppendEntries. */
+
+int config_marker_encode(uint64_t version_tag, const uint8_t sha256[32],
+                         uint8_t *buf, size_t bufsz, size_t *out_len)
+{
+    if (!sha256 || !buf || !out_len)
+        return -EINVAL;
+    if (bufsz < WAL_CONFIG_MARKER_PAYLOAD_LEN)
+        return -ENOSPC;
+
+    /* version_tag: 8 bytes, big-endian (matches config_repl wire convention). */
+    buf[0] = (uint8_t)(version_tag >> 56);
+    buf[1] = (uint8_t)(version_tag >> 48);
+    buf[2] = (uint8_t)(version_tag >> 40);
+    buf[3] = (uint8_t)(version_tag >> 32);
+    buf[4] = (uint8_t)(version_tag >> 24);
+    buf[5] = (uint8_t)(version_tag >> 16);
+    buf[6] = (uint8_t)(version_tag >> 8);
+    buf[7] = (uint8_t)(version_tag);
+
+    /* sha256: raw 32 bytes — the configuration *reference*, never the bytes. */
+    memcpy(buf + 8, sha256, 32);
+
+    *out_len = WAL_CONFIG_MARKER_PAYLOAD_LEN;
+    return 0;
+}
+
+int config_marker_decode(const uint8_t *buf, size_t len,
+                         uint64_t *version_tag, uint8_t sha256_out[32])
+{
+    if (!buf || len < WAL_CONFIG_MARKER_PAYLOAD_LEN)
+        return -EINVAL;
+
+    if (version_tag) {
+        *version_tag = ((uint64_t)buf[0] << 56) | ((uint64_t)buf[1] << 48) |
+                       ((uint64_t)buf[2] << 40) | ((uint64_t)buf[3] << 32) |
+                       ((uint64_t)buf[4] << 24) | ((uint64_t)buf[5] << 16) |
+                       ((uint64_t)buf[6] << 8)  | ((uint64_t)buf[7]);
+    }
+    if (sha256_out)
+        memcpy(sha256_out, buf + 8, 32);
+
+    return 0;
+}
+
 /* SSL context for xce_probe_config_tag.
  * Stored as void* to avoid SSL_CTX type at this point in the translation unit. */
 static void *s_probe_ssl_ctx = NULL;