diff --git a/include/amduat/asl/asl_store_index_fs.h b/include/amduat/asl/asl_store_index_fs.h
index 1b19028..d00c20a 100644
--- a/include/amduat/asl/asl_store_index_fs.h
+++ b/include/amduat/asl/asl_store_index_fs.h
@@ -43,6 +43,10 @@ typedef struct {
   uint64_t last_ingest_time_ns;
   amduat_asl_snapshot_id_t next_snapshot_id;
   bool snapshot_state_initialized;
+  bool log_tail_initialized;
+  uint64_t log_tail_logseq;
+  uint8_t log_tail_hash[32];
+  bool skip_exists_precheck;
   void *open_segments;
   pthread_mutex_t write_mutex;
   uint32_t write_depth;
diff --git a/src/adapters/asl_store_index_fs/asl_store_index_fs.c b/src/adapters/asl_store_index_fs/asl_store_index_fs.c
index bcf2114..7a969df 100644
--- a/src/adapters/asl_store_index_fs/asl_store_index_fs.c
+++ b/src/adapters/asl_store_index_fs/asl_store_index_fs.c
@@ -138,6 +138,19 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_impl(
     amduat_reference_t *out_ref,
     amduat_asl_index_state_t *out_state);
 
+static bool amduat_asl_store_index_fs_env_truthy(const char *value) {
+  if (value == NULL || value[0] == '\0') {
+    return false;
+  }
+  if (strcmp(value, "1") == 0 || strcmp(value, "true") == 0 ||
+      strcmp(value, "TRUE") == 0 || strcmp(value, "yes") == 0 ||
+      strcmp(value, "YES") == 0 || strcmp(value, "on") == 0 ||
+      strcmp(value, "ON") == 0) {
+    return true;
+  }
+  return false;
+}
+
 static int amduat_asl_store_index_fs_lockfile_acquire(
     amduat_asl_store_index_fs_t *fs) {
   char lock_path[AMDUAT_ASL_STORE_INDEX_FS_ROOT_MAX + 32];
@@ -194,6 +207,8 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_begin_write(
       return AMDUAT_ASL_STORE_ERR_IO;
     }
     fs->write_lock_fd = lock_fd;
+    /* Another store instance may have appended while we were unlocked. */
+    fs->log_tail_initialized = false;
   }
   fs->write_depth += 1u;
   return AMDUAT_ASL_STORE_OK;
@@ -1193,28 +1208,6 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_load_log(
   return AMDUAT_ASL_STORE_OK;
 }
 
-static amduat_asl_store_error_t amduat_asl_store_index_fs_write_log(
-    const char *log_path,
-    const char *log_dir,
-    amduat_asl_log_record_t *records,
-    size_t record_count) {
-  amduat_octets_t log_bytes;
-  amduat_asl_store_index_fs_write_status_t status;
-
-  if (!amduat_enc_asl_log_encode_v1(records, record_count, &log_bytes)) {
-    return AMDUAT_ASL_STORE_ERR_IO;
-  }
-
-  status = amduat_asl_store_index_fs_write_replace(log_dir, log_path,
-                                                   log_bytes.data,
-                                                   log_bytes.len);
-  amduat_octets_free(&log_bytes);
-  if (status == AMDUAT_ASL_STORE_INDEX_FS_WRITE_OK) {
-    return AMDUAT_ASL_STORE_OK;
-  }
-  return AMDUAT_ASL_STORE_ERR_IO;
-}
-
 static bool amduat_asl_store_index_fs_encode_artifact_ref(
     amduat_reference_t ref,
     uint8_t *out,
@@ -1250,6 +1243,240 @@ static bool amduat_asl_store_index_fs_encode_artifact_ref(
   return true;
 }
 
+static amduat_asl_store_error_t amduat_asl_store_index_fs_load_log_tail(
+    const char *log_path,
+    uint64_t *out_last_logseq,
+    uint8_t out_last_hash[AMDUAT_ASL_STORE_INDEX_FS_LOG_HASH_LEN]) {
+  int fd;
+  uint8_t *header_bytes = NULL;
+  size_t header_size = 0u;
+  uint64_t last_logseq = 0u;
+  uint8_t prev_hash[AMDUAT_ASL_STORE_INDEX_FS_LOG_HASH_LEN];
+  bool seen_record = false;
+
+  if (log_path == NULL || out_last_logseq == NULL || out_last_hash == NULL) {
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+
+  memset(prev_hash, 0, sizeof(prev_hash));
+  fd = open(log_path, O_RDONLY);
+  if (fd < 0) {
+    if (errno == ENOENT || errno == ENOTDIR) {
+      *out_last_logseq = 0u;
+      memcpy(out_last_hash, prev_hash, sizeof(prev_hash));
+      return AMDUAT_ASL_STORE_OK;
+    }
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+
+  if (!amduat_asl_store_index_fs_log_read_header_bytes(fd,
+                                                       &header_bytes,
+                                                       &header_size)) {
+    close(fd);
+    return AMDUAT_ASL_STORE_ERR_INTEGRITY;
+  }
+  free(header_bytes);
+  (void)header_size;
+
+  while (true) {
+    uint8_t record_header[16];
+    uint64_t logseq;
+    uint32_t record_type;
+    uint32_t payload_len;
+    uint8_t *payload = NULL;
+    uint8_t record_hash[AMDUAT_ASL_STORE_INDEX_FS_LOG_HASH_LEN];
+    uint8_t expected_hash[AMDUAT_ASL_STORE_INDEX_FS_LOG_HASH_LEN];
+    int rc;
+
+    rc = amduat_asl_store_index_fs_log_read_exact_eof(fd,
+                                                      record_header,
+                                                      sizeof(record_header));
+    if (rc == 0) {
+      break;
+    }
+    if (rc < 0) {
+      close(fd);
+      return AMDUAT_ASL_STORE_ERR_INTEGRITY;
+    }
+
+    logseq = amduat_asl_store_index_fs_load_u64_le(record_header);
+    if (seen_record && logseq <= last_logseq) {
+      close(fd);
+      return AMDUAT_ASL_STORE_ERR_INTEGRITY;
+    }
+    record_type =
+        amduat_asl_store_index_fs_log_load_u32_le(record_header + 8u);
+    payload_len =
+        amduat_asl_store_index_fs_log_load_u32_le(record_header + 12u);
+
+    if (payload_len != 0u) {
+      payload = (uint8_t *)malloc(payload_len);
+      if (payload == NULL) {
+        close(fd);
+        return AMDUAT_ASL_STORE_ERR_IO;
+      }
+      if (!amduat_asl_store_index_fs_log_read_exact(fd,
+                                                    payload,
+                                                    payload_len)) {
+        free(payload);
+        close(fd);
+        return AMDUAT_ASL_STORE_ERR_INTEGRITY;
+      }
+    }
+
+    if (!amduat_asl_store_index_fs_log_read_exact(fd,
+                                                  record_hash,
+                                                  sizeof(record_hash))) {
+      free(payload);
+      close(fd);
+      return AMDUAT_ASL_STORE_ERR_INTEGRITY;
+    }
+
+    if (!amduat_asl_store_index_fs_log_hash_record(prev_hash,
+                                                   logseq,
+                                                   record_type,
+                                                   payload_len,
+                                                   payload,
+                                                   expected_hash) ||
+        memcmp(expected_hash, record_hash, sizeof(record_hash)) != 0) {
+      free(payload);
+      close(fd);
+      return AMDUAT_ASL_STORE_ERR_INTEGRITY;
+    }
+
+    memcpy(prev_hash, record_hash, sizeof(prev_hash));
+    last_logseq = logseq;
+    seen_record = true;
+    free(payload);
+  }
+
+  close(fd);
+  *out_last_logseq = last_logseq;
+  memcpy(out_last_hash, prev_hash, sizeof(prev_hash));
+  return AMDUAT_ASL_STORE_OK;
+}
+
+static amduat_asl_store_error_t amduat_asl_store_index_fs_append_log_record_file(
+    const char *index_path,
+    const char *log_path,
+    uint64_t prev_logseq,
+    const uint8_t prev_hash[AMDUAT_ASL_STORE_INDEX_FS_LOG_HASH_LEN],
+    uint32_t record_type,
+    const uint8_t *payload,
+    size_t payload_len,
+    uint64_t *out_new_logseq,
+    uint8_t out_new_hash[AMDUAT_ASL_STORE_INDEX_FS_LOG_HASH_LEN]) {
+  int fd = -1;
+  struct stat st;
+  bool needs_header = false;
+  uint8_t *header_bytes = NULL;
+  size_t header_size = 0u;
+  uint8_t record_header[16];
+  uint8_t record_hash[AMDUAT_ASL_STORE_INDEX_FS_LOG_HASH_LEN];
+  uint64_t new_logseq;
+
+  if (index_path == NULL || log_path == NULL || prev_hash == NULL ||
+      out_new_logseq == NULL || out_new_hash == NULL) {
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+  if (payload_len != 0u && payload == NULL) {
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+  if (payload_len > UINT32_MAX || prev_logseq == UINT64_MAX) {
+    return AMDUAT_ASL_STORE_ERR_UNSUPPORTED;
+  }
+
+  new_logseq = prev_logseq + 1u;
+
+  fd = open(log_path, O_RDWR | O_CREAT, 0644);
+  if (fd < 0) {
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+  if (fstat(fd, &st) != 0) {
+    close(fd);
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+  needs_header = st.st_size == 0;
+  if (!needs_header) {
+    if (lseek(fd, 0, SEEK_SET) < 0) {
+      close(fd);
+      return AMDUAT_ASL_STORE_ERR_IO;
+    }
+    if (!amduat_asl_store_index_fs_log_read_header_bytes(fd,
+                                                         &header_bytes,
+                                                         &header_size)) {
+      close(fd);
+      return AMDUAT_ASL_STORE_ERR_INTEGRITY;
+    }
+    free(header_bytes);
+    (void)header_size;
+  }
+  if (lseek(fd, 0, SEEK_END) < 0) {
+    close(fd);
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+  if (needs_header) {
+    uint8_t header[AMDUAT_ASL_STORE_INDEX_FS_LOG_HEADER_LEN];
+    memcpy(header,
+           k_amduat_asl_store_index_fs_log_magic,
+           AMDUAT_ASL_STORE_INDEX_FS_LOG_MAGIC_LEN);
+    amduat_asl_store_index_fs_log_store_u32_le(
+        header + AMDUAT_ASL_STORE_INDEX_FS_LOG_MAGIC_LEN,
+        AMDUAT_ASL_STORE_INDEX_FS_LOG_VERSION);
+    amduat_asl_store_index_fs_log_store_u32_le(
+        header + AMDUAT_ASL_STORE_INDEX_FS_LOG_MAGIC_LEN + 4u,
+        AMDUAT_ASL_STORE_INDEX_FS_LOG_HEADER_LEN);
+    amduat_asl_store_index_fs_log_store_u64_le(
+        header + AMDUAT_ASL_STORE_INDEX_FS_LOG_MAGIC_LEN + 8u,
+        0u);
+    if (!amduat_asl_store_index_fs_log_write_exact(fd, header, sizeof(header))) {
+      close(fd);
+      return AMDUAT_ASL_STORE_ERR_IO;
+    }
+  }
+
+  if (!amduat_asl_store_index_fs_log_hash_record(prev_hash,
+                                                 new_logseq,
+                                                 record_type,
+                                                 (uint32_t)payload_len,
+                                                 payload,
+                                                 record_hash)) {
+    close(fd);
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+
+  amduat_asl_store_index_fs_log_store_u64_le(record_header, new_logseq);
+  amduat_asl_store_index_fs_log_store_u32_le(record_header + 8u, record_type);
+  amduat_asl_store_index_fs_log_store_u32_le(record_header + 12u,
+                                             (uint32_t)payload_len);
+  if (!amduat_asl_store_index_fs_log_write_exact(fd,
+                                                 record_header,
+                                                 sizeof(record_header)) ||
+      (payload_len != 0u &&
+       !amduat_asl_store_index_fs_log_write_exact(fd, payload, payload_len)) ||
+      !amduat_asl_store_index_fs_log_write_exact(fd,
+                                                 record_hash,
+                                                 sizeof(record_hash))) {
+    close(fd);
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+
+  if (fsync(fd) != 0) {
+    close(fd);
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+  if (close(fd) != 0) {
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+  if (!amduat_asl_store_index_fs_fsync_directory(index_path)) {
+    return AMDUAT_ASL_STORE_ERR_IO;
+  }
+
+  *out_new_logseq = new_logseq;
+  memcpy(out_new_hash, record_hash, sizeof(record_hash));
+  return AMDUAT_ASL_STORE_OK;
+}
+
 static amduat_asl_store_error_t amduat_asl_store_index_fs_append_log_record_unlocked(
     amduat_asl_store_index_fs_t *fs,
     uint32_t record_type,
@@ -1258,11 +1485,8 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_append_log_record_unlo
     amduat_asl_index_state_t *out_state) {
   char *index_path = NULL;
   char *log_path = NULL;
-  amduat_asl_log_record_t *log_records = NULL;
-  size_t log_count = 0u;
-  amduat_asl_log_record_t *next = NULL;
-  uint64_t new_logseq;
-  uint8_t *payload_copy = NULL;
+  uint64_t new_logseq = 0u;
+  uint8_t new_hash[AMDUAT_ASL_STORE_INDEX_FS_LOG_HASH_LEN];
   amduat_asl_store_error_t err;
 
   if (fs == NULL) {
@@ -1287,74 +1511,38 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_append_log_record_unlo
     return AMDUAT_ASL_STORE_ERR_IO;
   }
 
-  err = amduat_asl_store_index_fs_load_log(log_path, &log_records, &log_count);
-  if (err != AMDUAT_ASL_STORE_OK) {
-    amduat_asl_store_index_fs_log_free(log_records, log_count);
-    free(log_path);
-    free(index_path);
-    return err;
-  }
-  if (log_count != 0u && log_records == NULL) {
-    free(log_path);
-    free(index_path);
-    return AMDUAT_ASL_STORE_ERR_IO;
-  }
-
-  if (log_count == 0u) {
-    log_records = (amduat_asl_log_record_t *)calloc(1u,
-                                                    sizeof(*log_records));
-    if (log_records == NULL) {
+  if (!fs->log_tail_initialized) {
+    err = amduat_asl_store_index_fs_load_log_tail(log_path,
+                                                  &fs->log_tail_logseq,
+                                                  fs->log_tail_hash);
+    if (err != AMDUAT_ASL_STORE_OK) {
       free(log_path);
       free(index_path);
-      return AMDUAT_ASL_STORE_ERR_IO;
+      return err;
     }
-    new_logseq = 1u;
-  } else {
-    if (log_records[log_count - 1u].logseq == UINT64_MAX) {
-      amduat_asl_store_index_fs_log_free(log_records, log_count);
-      free(log_path);
-      free(index_path);
-      return AMDUAT_ASL_STORE_ERR_IO;
-    }
-    new_logseq = log_records[log_count - 1u].logseq + 1u;
-    next = (amduat_asl_log_record_t *)realloc(
-        log_records, (log_count + 1u) * sizeof(*log_records));
-    if (next == NULL) {
-      amduat_asl_store_index_fs_log_free(log_records, log_count);
-      free(log_path);
-      free(index_path);
-      return AMDUAT_ASL_STORE_ERR_IO;
-    }
-    log_records = next;
+    fs->log_tail_initialized = true;
   }
 
-  if (payload_len != 0u) {
-    payload_copy = (uint8_t *)malloc(payload_len);
-    if (payload_copy == NULL) {
-      amduat_asl_store_index_fs_log_free(log_records, log_count);
-      free(log_path);
-      free(index_path);
-      return AMDUAT_ASL_STORE_ERR_IO;
-    }
-    memcpy(payload_copy, payload, payload_len);
-  }
-
-  log_records[log_count].logseq = new_logseq;
-  log_records[log_count].record_type = record_type;
-  log_records[log_count].payload = amduat_octets(payload_copy, payload_len);
-  memset(log_records[log_count].record_hash, 0,
-         sizeof(log_records[log_count].record_hash));
-  log_count += 1u;
-
-  err = amduat_asl_store_index_fs_write_log(log_path, index_path,
-                                            log_records, log_count);
-  amduat_asl_store_index_fs_log_free(log_records, log_count);
+  err = amduat_asl_store_index_fs_append_log_record_file(
+      index_path,
+      log_path,
+      fs->log_tail_logseq,
+      fs->log_tail_hash,
+      record_type,
+      payload,
+      payload_len,
+      &new_logseq,
+      new_hash);
   free(log_path);
   free(index_path);
   if (err != AMDUAT_ASL_STORE_OK) {
     return err;
   }
 
+  fs->log_tail_logseq = new_logseq;
+  memcpy(fs->log_tail_hash, new_hash, sizeof(new_hash));
+  fs->log_tail_initialized = true;
+
   if (out_state != NULL &&
       !amduat_asl_store_index_fs_current_state_impl(fs, out_state)) {
     return AMDUAT_ASL_STORE_ERR_IO;
@@ -4114,6 +4302,7 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_unlocked_i
   amduat_reference_t derived_ref;
   amduat_octets_t artifact_bytes;
   amduat_asl_index_state_t current_state;
+  bool has_current_state = false;
   amduat_artifact_t existing_artifact;
   amduat_asl_store_error_t err;
   char *index_path;
@@ -4121,7 +4310,6 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_unlocked_i
   char *blocks_path;
   char *segment_path;
   char *block_path;
-  char *log_path;
   uint16_t shard_id;
   uint64_t segment_id;
   uint64_t local_segment_id;
@@ -4130,11 +4318,8 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_unlocked_i
   amduat_asl_extent_record_t extent;
   amduat_octets_t segment_bytes;
   uint8_t segment_hash[AMDUAT_ASL_STORE_INDEX_FS_SEGMENT_HASH_LEN];
-  amduat_asl_log_record_t *log_records;
-  size_t log_count;
   uint8_t *seal_payload;
   size_t seal_len;
-  uint64_t new_logseq;
   amduat_asl_store_index_fs_write_status_t write_status;
   size_t artifact_len;
 
@@ -4163,29 +4348,32 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_unlocked_i
                                                    fs->shard_count);
   }
 
-  if (!amduat_asl_store_index_fs_current_state_impl(ctx, &current_state)) {
-    amduat_reference_free(&derived_ref);
-    amduat_octets_free(&artifact_bytes);
-    return AMDUAT_ASL_STORE_ERR_IO;
-  }
+  if (!fs->skip_exists_precheck) {
+    if (!amduat_asl_store_index_fs_current_state_impl(ctx, &current_state)) {
+      amduat_reference_free(&derived_ref);
+      amduat_octets_free(&artifact_bytes);
+      return AMDUAT_ASL_STORE_ERR_IO;
+    }
+    has_current_state = true;
 
-  existing_artifact = amduat_artifact(amduat_octets(NULL, 0u));
-  err = amduat_asl_store_index_fs_get_indexed_impl(ctx, derived_ref,
-                                                   current_state,
-                                                   &existing_artifact);
-  if (err == AMDUAT_ASL_STORE_OK) {
-    amduat_artifact_free(&existing_artifact);
-    *out_ref = derived_ref;
-    amduat_asl_store_index_fs_fill_index_state(out_state,
-                                               current_state.snapshot_id,
-                                               current_state.log_position);
-    amduat_octets_free(&artifact_bytes);
-    return AMDUAT_ASL_STORE_OK;
-  }
-  if (err != AMDUAT_ASL_STORE_ERR_NOT_FOUND) {
-    amduat_reference_free(&derived_ref);
-    amduat_octets_free(&artifact_bytes);
-    return err;
+    existing_artifact = amduat_artifact(amduat_octets(NULL, 0u));
+    err = amduat_asl_store_index_fs_get_indexed_impl(ctx, derived_ref,
+                                                     current_state,
+                                                     &existing_artifact);
+    if (err == AMDUAT_ASL_STORE_OK) {
+      amduat_artifact_free(&existing_artifact);
+      *out_ref = derived_ref;
+      amduat_asl_store_index_fs_fill_index_state(out_state,
+                                                 current_state.snapshot_id,
+                                                 current_state.log_position);
+      amduat_octets_free(&artifact_bytes);
+      return AMDUAT_ASL_STORE_OK;
+    }
+    if (err != AMDUAT_ASL_STORE_ERR_NOT_FOUND) {
+      amduat_reference_free(&derived_ref);
+      amduat_octets_free(&artifact_bytes);
+      return err;
+    }
   }
 
   if (fs->segment_policy.small_artifact_threshold != 0u &&
@@ -4205,6 +4393,12 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_unlocked_i
         amduat_asl_store_index_fs_open_segment_contains(open_segment,
                                                         derived_ref)) {
       *out_ref = derived_ref;
+      if (!has_current_state &&
+          !amduat_asl_store_index_fs_current_state_impl(ctx, &current_state)) {
+        amduat_octets_free(&artifact_bytes);
+        return AMDUAT_ASL_STORE_ERR_IO;
+      }
+      has_current_state = true;
       amduat_asl_store_index_fs_fill_index_state(out_state,
                                                  current_state.snapshot_id,
                                                  current_state.log_position);
@@ -4254,6 +4448,13 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_unlocked_i
         return err;
       }
     } else {
+      if (!has_current_state &&
+          !amduat_asl_store_index_fs_current_state_impl(ctx, &current_state)) {
+        amduat_reference_free(&derived_ref);
+        amduat_octets_free(&artifact_bytes);
+        return AMDUAT_ASL_STORE_ERR_IO;
+      }
+      has_current_state = true;
       amduat_asl_store_index_fs_fill_index_state(out_state,
                                                  current_state.snapshot_id,
                                                  current_state.log_position);
@@ -4470,75 +4671,11 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_unlocked_i
     return AMDUAT_ASL_STORE_ERR_IO;
   }
 
-  if (!amduat_asl_store_index_fs_layout_build_log_path(fs->root_path,
-                                                       &log_path)) {
-    amduat_reference_free(&derived_ref);
-    amduat_octets_free(&artifact_bytes);
-    free(index_path);
-    free(segments_path);
-    free(blocks_path);
-    return AMDUAT_ASL_STORE_ERR_IO;
-  }
-
-  log_records = NULL;
-  log_count = 0u;
-  err = amduat_asl_store_index_fs_load_log(log_path, &log_records, &log_count);
-  if (err != AMDUAT_ASL_STORE_OK) {
-    amduat_reference_free(&derived_ref);
-    amduat_octets_free(&artifact_bytes);
-    amduat_asl_store_index_fs_log_free(log_records, log_count);
-    free(log_path);
-    free(index_path);
-    free(segments_path);
-    free(blocks_path);
-    return err;
-  }
-
-  if (log_count != 0u && log_records == NULL) {
-    amduat_reference_free(&derived_ref);
-    amduat_octets_free(&artifact_bytes);
-    free(log_path);
-    free(index_path);
-    free(segments_path);
-    free(blocks_path);
-    return AMDUAT_ASL_STORE_ERR_IO;
-  }
-
-  if (log_count == 0u) {
-    log_records = (amduat_asl_log_record_t *)calloc(1u,
-                                                    sizeof(*log_records));
-    if (log_records == NULL) {
-      amduat_reference_free(&derived_ref);
-      amduat_octets_free(&artifact_bytes);
-      free(log_path);
-      free(index_path);
-      free(segments_path);
-      free(blocks_path);
-      return AMDUAT_ASL_STORE_ERR_IO;
-    }
-  } else {
-    amduat_asl_log_record_t *next = (amduat_asl_log_record_t *)realloc(
-        log_records, (log_count + 1u) * sizeof(*log_records));
-    if (next == NULL) {
-      amduat_reference_free(&derived_ref);
-      amduat_octets_free(&artifact_bytes);
-      amduat_enc_asl_log_free(log_records, log_count);
-      free(log_path);
-      free(index_path);
-      free(segments_path);
-      free(blocks_path);
-      return AMDUAT_ASL_STORE_ERR_IO;
-    }
-    log_records = next;
-  }
-
   seal_len = 8u + AMDUAT_ASL_STORE_INDEX_FS_SEGMENT_HASH_LEN;
   seal_payload = (uint8_t *)malloc(seal_len);
   if (seal_payload == NULL) {
     amduat_reference_free(&derived_ref);
     amduat_octets_free(&artifact_bytes);
-    amduat_asl_store_index_fs_log_free(log_records, log_count);
-    free(log_path);
     free(index_path);
     free(segments_path);
     free(blocks_path);
@@ -4554,34 +4691,13 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_unlocked_i
   seal_payload[6] = (uint8_t)((segment_id >> 48) & 0xffu);
   seal_payload[7] = (uint8_t)((segment_id >> 56) & 0xffu);
   memcpy(seal_payload + 8, segment_hash, sizeof(segment_hash));
-
-  if (log_count == 0u) {
-    new_logseq = 1u;
-  } else {
-    if (log_records[log_count - 1u].logseq == UINT64_MAX) {
-      amduat_reference_free(&derived_ref);
-      amduat_octets_free(&artifact_bytes);
-      amduat_asl_store_index_fs_log_free(log_records, log_count);
-      free(log_path);
-      free(index_path);
-      free(segments_path);
-      free(blocks_path);
-      free(seal_payload);
-      return AMDUAT_ASL_STORE_ERR_IO;
-    }
-    new_logseq = log_records[log_count - 1u].logseq + 1u;
-  }
-  log_records[log_count].logseq = new_logseq;
-  log_records[log_count].record_type = AMDUAT_ASL_LOG_RECORD_SEGMENT_SEAL;
-  log_records[log_count].payload = amduat_octets(seal_payload, seal_len);
-  memset(log_records[log_count].record_hash, 0,
-         sizeof(log_records[log_count].record_hash));
-  log_count += 1u;
-
-  err = amduat_asl_store_index_fs_write_log(log_path, index_path,
-                                            log_records, log_count);
-  amduat_asl_store_index_fs_log_free(log_records, log_count);
-  free(log_path);
+  err = amduat_asl_store_index_fs_append_log_record_unlocked(
+      fs,
+      AMDUAT_ASL_LOG_RECORD_SEGMENT_SEAL,
+      seal_payload,
+      seal_len,
+      NULL);
+  free(seal_payload);
   free(index_path);
   free(segments_path);
   free(blocks_path);
@@ -4596,7 +4712,7 @@ static amduat_asl_store_error_t amduat_asl_store_index_fs_put_indexed_unlocked_i
   *out_ref = derived_ref;
   amduat_asl_store_index_fs_fill_index_state(out_state,
                                              current_state.snapshot_id,
-                                             new_logseq);
+                                             fs->log_tail_logseq);
   amduat_asl_store_index_fs_update_ingest_state(fs, artifact_len);
   amduat_asl_store_index_fs_maybe_snapshot_size(fs);
   return AMDUAT_ASL_STORE_OK;
@@ -4800,6 +4916,7 @@ amduat_asl_store_error_t amduat_asl_store_index_fs_snapshot_create(
     free(manifest_path);
     return err;
   }
+  fs->log_tail_initialized = false;
 
   {
     amduat_asl_snapshot_manifest_t verify_manifest;
@@ -5224,6 +5341,11 @@ bool amduat_asl_store_index_fs_init(amduat_asl_store_index_fs_t *fs,
   fs->last_ingest_time_ns = 0u;
   fs->next_snapshot_id = 0u;
   fs->snapshot_state_initialized = false;
+  fs->log_tail_initialized = false;
+  fs->log_tail_logseq = 0u;
+  memset(fs->log_tail_hash, 0, sizeof(fs->log_tail_hash));
+  fs->skip_exists_precheck = amduat_asl_store_index_fs_env_truthy(
+      getenv("AMDUAT_ASL_INDEX_FS_SKIP_EXISTS_PRECHECK"));
   fs->open_segments = NULL;
   fs->write_depth = 0u;
   fs->write_lock_fd = -1;