perf: batch connection inserts in ingest_connections

Replace one INSERT per event (up to FETCH_LIMIT auto-committed
round trips per node per poll) with multi-row INSERTs in chunks of
200, wrapped in a single transaction per node. Same data, one
commit instead of hundreds, which was making fetch runs slower as
the table grew.

includes/functions.php

@@ -75,19 +75,16 @@ function fetch_node_api(array $node, string $path): mixed {
  * Ingest connection events from portspoof_py that are strictly newer than
  * $last_event_at (ISO 8601 string, or null to ingest everything).
  *
+ * New rows are written with multi-row INSERTs in chunks, inside a single
+ * transaction per call, to keep the number of round trips and commits low.
+ *
  * Returns ['inserted' => int, 'new_max_ts' => string|null]
  * where new_max_ts is the DATETIME(6) of the newest row inserted, or null if
  * nothing new was inserted.
  */
 function ingest_connections(int $node_id, array $events, ?string $last_event_at): array {
-    $inserted   = 0;
     $new_max_ts = null;
-
-    $s = db()->prepare(
-        'INSERT INTO connections
-         (node_id, occurred_at, src_ip, src_port, dst_port, banner_hex, banner_len)
-         VALUES (?, ?, ?, ?, ?, ?, ?)'
-    );
+    $rows       = [];
 
     foreach ($events as $ev) {
         $raw_ts = $ev['timestamp'] ?? null;
@@ -103,7 +100,7 @@ function ingest_connections(int $node_id, array $events, ?string $last_event_at)
             continue;
         }
 
-        $s->execute([
+        $rows[] = [
             $node_id,
             $ts,
             $ev['src_ip']   ?? '',
@@ -111,15 +108,40 @@ function ingest_connections(int $node_id, array $events, ?string $last_event_at)
             (int)($ev['dst_port']  ?? 0),
             $ev['banner_hex'] ?? null,
             (int)($ev['banner_len'] ?? 0),
-        ]);
-        $inserted++;
+        ];
 
         if ($new_max_ts === null || $ts > $new_max_ts) {
             $new_max_ts = $ts;
         }
     }
 
-    return ['inserted' => $inserted, 'new_max_ts' => $new_max_ts];
+    if ($rows === []) {
+        return ['inserted' => 0, 'new_max_ts' => null];
+    }
+
+    $pdo = db();
+    $pdo->beginTransaction();
+    try {
+        foreach (array_chunk($rows, 200) as $chunk) {
+            $values = implode(', ', array_fill(0, count($chunk), '(?, ?, ?, ?, ?, ?, ?)'));
+            $params = [];
+            foreach ($chunk as $r) {
+                $params = array_merge($params, $r);
+            }
+            $s = $pdo->prepare(
+                'INSERT INTO connections
+                 (node_id, occurred_at, src_ip, src_port, dst_port, banner_hex, banner_len)
+                 VALUES ' . $values
+            );
+            $s->execute($params);
+        }
+        $pdo->commit();
+    } catch (PDOException $e) {
+        $pdo->rollBack();
+        throw $e;
+    }
+
+    return ['inserted' => count($rows), 'new_max_ts' => $new_max_ts];
 }
 
 /**