diff --git a/apps/webapp/app/entry.server.tsx b/apps/webapp/app/entry.server.tsx
index db72b0364c..60c234402d 100644
--- a/apps/webapp/app/entry.server.tsx
+++ b/apps/webapp/app/entry.server.tsx
@@ -30,8 +30,17 @@ import {
 // on webapp startup. The singleton's initializer wires start (gated on
 // `clickhouseFactory.isReady()`) and SIGTERM/SIGINT shutdown — mirrors
 // runsReplicationInstance.
+//
+// IMPORTANT: do NOT replace this with `void sessionsReplicationInstance;`.
+// `apps/webapp/package.json` declares `"sideEffects": false`, so esbuild
+// treats `void <identifier>;` as a pure expression statement and tree-shakes
+// the entire import — the singleton's initializer never fires and the
+// sessions→ClickHouse logical replication slot stops being consumed. Assigning
+// to globalThis is an unambiguous side effect the bundler must preserve. See
+// TRI-9864 for the incident write-up.
 import { sessionsReplicationInstance } from "./services/sessionsReplicationInstance.server";
-void sessionsReplicationInstance;
+(globalThis as Record<string, unknown>).__sessionsReplicationInstance =
+  sessionsReplicationInstance;
 
 const ABORT_DELAY = 30000;
 
diff --git a/apps/webapp/app/v3/services/adminWorker.server.ts b/apps/webapp/app/v3/services/adminWorker.server.ts
index 2e4d1b066c..cf3dbd57c6 100644
--- a/apps/webapp/app/v3/services/adminWorker.server.ts
+++ b/apps/webapp/app/v3/services/adminWorker.server.ts
@@ -6,10 +6,16 @@ import { logger } from "~/services/logger.server";
 import { runsReplicationInstance } from "~/services/runsReplicationInstance.server";
 // Reference-hold the sessions-replication singleton so module evaluation runs
 // its initializer (creates the ClickHouse client, subscribes to the logical
-// replication slot, wires signal handlers) when the webapp boots. A bare
-// side-effect import gets tree-shaken by the bundler.
+// replication slot, wires signal handlers) when the webapp boots.
+//
+// IMPORTANT: do NOT replace with `void sessionsReplicationInstance;`. With
+// `"sideEffects": false` in apps/webapp/package.json, esbuild treats `void X;`
+// as a pure expression statement and eliminates the import — the singleton
+// initializer never fires. Assignment to globalThis is an observable side
+// effect the bundler must preserve. See TRI-9864.
 import { sessionsReplicationInstance } from "~/services/sessionsReplicationInstance.server";
-void sessionsReplicationInstance;
+(globalThis as Record<string, unknown>).__sessionsReplicationInstance =
+  sessionsReplicationInstance;
 import { singleton } from "~/utils/singleton";
 import { tracer } from "../tracer.server";
 import { $replica } from "~/db.server";