diff --git a/imports/startup/server/calcUnionAsync.js b/imports/startup/server/calcUnionAsync.js
index 0eaa57f..b5ad54a 100644
--- a/imports/startup/server/calcUnionAsync.js
+++ b/imports/startup/server/calcUnionAsync.js
@@ -1,18 +1,24 @@
 import path from 'path';
 import { Worker } from 'worker_threads';
 
-// Meteor only bundles the npm packages it sees imported/required somewhere in
-// its own compiled module graph. The actual usage of these three is inside
-// private/workers/unionWorker.js, a plain asset file Meteor's bundler never
-// traces (it's loaded at runtime via new Worker(), not import/require here).
-// Without this, `meteor build` drops them from programs/server/node_modules
-// and the worker fails at startup with "Cannot find module '@turf/circle'".
-import '@turf/circle';
-import '@turf/union';
-import '@turf/truncate';
-
 const WORKER_PATH = path.resolve(process.cwd(), 'assets/app/workers/unionWorker.js');
 
+// The app's own npm dependencies (installed by `meteor build`) live in
+// programs/server/npm/node_modules — a directory that's a SIBLING of
+// programs/server/assets, not an ancestor of it. Node's require() only walks
+// up parent directories looking for node_modules, so a plain
+// require('@turf/circle') from the worker script (a raw asset, not part of
+// Meteor's own module system that knows about this layout) can never find it
+// and fails with "Cannot find module '@turf/circle'". Resolving the absolute
+// path here, where Meteor's own module system already knows how to find it,
+// and handing it to the worker sidesteps that entirely.
+const NPM_MODULES = path.resolve(process.cwd(), 'programs/server/npm/node_modules');
+const turfPaths = {
+  circle: path.join(NPM_MODULES, '@turf/circle'),
+  union: path.join(NPM_MODULES, '@turf/union'),
+  truncate: path.join(NPM_MODULES, '@turf/truncate')
+};
+
 /**
  * Circle-union of already-validated, already-decorated subscriptions, run in a
  * worker thread so the main event loop (DDP/HTTP) stays free regardless of
@@ -21,7 +27,7 @@ const WORKER_PATH = path.resolve(process.cwd(), 'assets/app/workers/unionWorker.
  * are merged into it instead of a union computed from scratch.
  */
 const calcUnionAsync = (subs, baseUnion = null) => new Promise((resolve, reject) => {
-  const worker = new Worker(WORKER_PATH, { workerData: { subs, baseUnion } });
+  const worker = new Worker(WORKER_PATH, { workerData: { subs, baseUnion, turfPaths } });
   worker.once('message', (msg) => {
     worker.terminate();
     if (msg.error) {
diff --git a/private/workers/unionWorker.js b/private/workers/unionWorker.js
index f6fc9ec..34c8156 100644
--- a/private/workers/unionWorker.js
+++ b/private/workers/unionWorker.js
@@ -15,10 +15,20 @@
 // subs gets merged into (the incremental-add fast path) instead of starting
 // from scratch — for a single new subscription this is one tunion() call
 // instead of redoing the whole chain over every subscription again.
+// workerData.turfPaths gives absolute paths to @turf/circle, @turf/union and
+// @turf/truncate — this file lives under programs/server/assets/, while the
+// app's own npm deps live in the sibling programs/server/npm/node_modules,
+// which plain require('@turf/circle') can never find by walking up parent
+// directories. The caller resolves the paths (it's Meteor-compiled code that
+// knows how to find them) and hands them over instead.
 const { parentPort, workerData } = require('worker_threads');
-const tcircle = require('@turf/circle').default;
-const tunion = require('@turf/union').default;
-const ttrunc = require('@turf/truncate').default;
+
+// eslint-disable-next-line import/no-dynamic-require
+const tcircle = require(workerData.turfPaths.circle).default;
+// eslint-disable-next-line import/no-dynamic-require
+const tunion = require(workerData.turfPaths.union).default;
+// eslint-disable-next-line import/no-dynamic-require
+const ttrunc = require(workerData.turfPaths.truncate).default;
 
 const truncOptions = { precision: 6, coordinates: 2 };