fix(ha-repl-hardening): wire snapshot production path (task 3.5b)

- SEND_SNAPSHOT uses checkpoint_lsn (not committed_lsn) for file lookup
- ha_send_snapshot_to_standby stats file for actual total_size
- ha_compute_oldest_wal_lsn scans WAL dir for min segment LSN
- Removed hardcoded 131072 and oldest_wal_lsn=0 placeholders

src/controller/config_repl.c

@@ -1740,16 +1740,21 @@ int (*xce_snapshot_chunk_hook)(endpoint_t *ep, xce_request_t *req) = NULL;
 #define SNAPSHOT_CHUNK_SIZE 65536
 
 int ha_send_snapshot_to_standby(endpoint_t *ep, const char *snap_dir,
-                                 uint64_t checkpoint_lsn, uint64_t total_size)
+                                 uint64_t checkpoint_lsn)
 {
     if (!snap_dir)
         return -EINVAL;
 
-    /* Find the snapshot file by naming convention */
     char snap_path[4096];
     snprintf(snap_path, sizeof(snap_path),
              "%s/snap-%016" PRIx64 ".capnp", snap_dir, checkpoint_lsn);
 
+    /* Stat the snapshot file to get total_size */
+    struct stat st;
+    if (stat(snap_path, &st) != 0)
+        return -errno;
+    uint64_t total_size = (uint64_t)st.st_size;
+
     FILE *f = fopen(snap_path, "rb");
     if (!f)
         return -errno;
@@ -1813,3 +1818,22 @@ int ha_send_snapshot_to_standby(endpoint_t *ep, const char *snap_dir,
     fclose(f);
     return rc;
 }
+
+uint64_t ha_compute_oldest_wal_lsn(const char *wal_path)
+{
+    DIR *d = opendir(wal_path);
+    if (!d)
+        return 0;
+
+    uint64_t oldest = UINT64_MAX;
+    struct dirent *ent;
+    while ((ent = readdir(d)) != NULL) {
+        uint64_t seg_lsn = 0;
+        if (sscanf(ent->d_name, "seg-%" SCNx64 ".wal", &seg_lsn) != 1)
+            continue;
+        if (seg_lsn < oldest)
+            oldest = seg_lsn;
+    }
+    closedir(d);
+    return (oldest == UINT64_MAX) ? 0 : oldest;
+}

src/controller/config_repl.h

@@ -158,7 +158,9 @@ int ha_stream_wal_to_standby(endpoint_t *ep, const char *wal_path,
 #define SNAPSHOT_CHUNK_SIZE 65536
 
 int ha_send_snapshot_to_standby(endpoint_t *ep, const char *snap_dir,
-                                 uint64_t checkpoint_lsn, uint64_t total_size);
+                                 uint64_t checkpoint_lsn);
+
+uint64_t ha_compute_oldest_wal_lsn(const char *wal_path);
 
 /*
  * handle_ctrlhello: primary-side handler for OP_hello from a joining standby.

src/controller/ha.c

@@ -1075,18 +1075,14 @@ int ha_dispatch_repl_action_for_standby(ha_state_t *ha,
         break;
 
     case HA_REPL_SEND_SNAPSHOT:
-        /* Task 3.5: snapshot transfer.
-         * Creates a checkpoint in the delaymgr thread (not here — vtask
-         * must not block), then sends the snapshot in 64KB chunks. */
         INFO("HA repl: standby[%d] lsn=%" PRIu64
              " < oldest_wal_lsn=%" PRIu64 " → requesting snapshot transfer",
              peer_idx, standby_lsn, oldest_wal_lsn);
         if (c && c->persist.snap_path[0]) {
             extern int ha_send_snapshot_to_standby(endpoint_t *, const char *,
-                                                    uint64_t, uint64_t);
+                                                    uint64_t);
             ha_send_snapshot_to_standby(ep, c->persist.snap_path,
-                                        c->persist.committed_lsn,
-                                        /*total_size placeholder*/ 131072);
+                                        c->persist.checkpoint_lsn);
         }
         break;
 
@@ -2249,12 +2245,15 @@ static int repl_ack_decode_and_dispatch(endpoint_t *ep, vote_ep_ctx_t *vctx)
                                      sr.config_tag, sr.applied_lsn,
                                      committed_tag, committed_lsn);
 
-            /* Task 3.3: run the unified decision loop for this standby.
-             * oldest_wal_lsn=0 until snapshot transfer is wired (Task 3.5). */
+            /* Derive oldest_wal_lsn from the WAL directory.
+             * The oldest retained segment's start LSN is the boundary —
+             * standbys below it need a snapshot (Task 3.5b). */
             uint64_t oldest_wal_lsn = 0;
 #ifndef XCE_TESTING
-            if (c)
-                oldest_wal_lsn = 0; /* Task 3.5: wire persist->oldest_wal_lsn */
+            if (c && c->persist.wal_path[0]) {
+                extern uint64_t ha_compute_oldest_wal_lsn(const char *wal_path);
+                oldest_wal_lsn = ha_compute_oldest_wal_lsn(c->persist.wal_path);
+            }
 #endif
             ha_dispatch_repl_action_for_standby(ha, c, ep, peer_idx,
                                                 committed_tag, committed_lsn,

src/controller/testsuite/test_config_repl.c

@@ -1548,8 +1548,8 @@ static void test_snapshot_transfer_two_chunks(void)
     xce_snapshot_chunk_hook = snaptest_hook;
     snaptest_reset();
 
-    extern int ha_send_snapshot_to_standby(endpoint_t *, const char *, uint64_t, uint64_t);
-    int rc = ha_send_snapshot_to_standby(NULL, tmpdir, lsn, 131072);
+    extern int ha_send_snapshot_to_standby(endpoint_t *, const char *, uint64_t);
+    int rc = ha_send_snapshot_to_standby(NULL, tmpdir, lsn);
     TEST_ASSERT_EQUAL_INT(0, rc);
 
     TEST_ASSERT_EQUAL_INT(2, g_snaptest_chunk_count);
@@ -1591,8 +1591,8 @@ static void test_snapshot_transfer_small_less_than_one_chunk(void)
     xce_snapshot_chunk_hook = snaptest_hook;
     snaptest_reset();
 
-    extern int ha_send_snapshot_to_standby(endpoint_t *, const char *, uint64_t, uint64_t);
-    int rc = ha_send_snapshot_to_standby(NULL, tmpdir, lsn, 64);
+    extern int ha_send_snapshot_to_standby(endpoint_t *, const char *, uint64_t);
+    int rc = ha_send_snapshot_to_standby(NULL, tmpdir, lsn);
     TEST_ASSERT_EQUAL_INT(0, rc);
 
     TEST_ASSERT_EQUAL_INT(1, g_snaptest_chunk_count);