fix(replication): correct Postgres epoch constant in replication client

The keepalive decode and standby status ack used 946080000000 as the
Postgres-to-Unix epoch offset (ms). That value is 1999-12-25, seven days
short of the real Postgres epoch (2000-01-01 = 946684800000). Replace both
literals with a shared POSTGRES_EPOCH_MS constant matching pgoutput.ts.

The affected timestamps are observability-only: the decoded keepalive
timestamp is unused by consumers, and the encoded standby-reply timestamp
only surfaces as pg_stat_replication.reply_time. WAL feedback is driven by
the LSN bytes, so slot advancement is unaffected.

Author: matt-aitken

internal-packages/replication/src/client.ts

@@ -9,6 +9,14 @@ import { LogicalReplicationClientError } from "./errors.js";
 import { PgoutputMessage, PgoutputParser, getPgoutputStartReplicationSQL } from "./pgoutput.js";
 import { startSpan, trace, Tracer } from "@internal/tracing";
 
+/**
+ * Milliseconds between the Unix epoch (1970-01-01) and the Postgres epoch
+ * (2000-01-01), used to convert between Postgres replication timestamps and
+ * `Date.now()`. Mirrors `(POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * USECS_PER_DAY`
+ * in pgoutput.ts (946684800000000 micros).
+ */
+const POSTGRES_EPOCH_MS = 946684800000;
+
 export interface LogicalReplicationClientOptions {
   /**
    * The pg client config.
@@ -363,7 +371,7 @@ export class LogicalReplicationClient {
         } else if (buffer[0] === 0x6b) {
           // Primary keepalive message
           const timestamp = Math.floor(
-            buffer.readUInt32BE(9) * 4294967.296 + buffer.readUInt32BE(13) / 1000 + 946080000000
+            buffer.readUInt32BE(9) * 4294967.296 + buffer.readUInt32BE(13) / 1000 + POSTGRES_EPOCH_MS
           );
           const shouldRespond = !!buffer.readInt8(17);
           this.events.emit("heartbeat", { lsn, timestamp, shouldRespond });
@@ -658,7 +666,7 @@ export class LogicalReplicationClient {
       const slice = lsn.split("/");
       let [upperWAL, lowerWAL]: [number, number] = [parseInt(slice[0], 16), parseInt(slice[1], 16)];
       // Timestamp as microseconds since midnight 2000-01-01
-      const now = Date.now() - 946080000000;
+      const now = Date.now() - POSTGRES_EPOCH_MS;
       const upperTimestamp = Math.floor(now / 4294967.296);
       const lowerTimestamp = Math.floor(now - upperTimestamp * 4294967.296);
       if (lowerWAL === 4294967295) {