diff --git a/.github/actions/setup-js/action.yaml b/.github/actions/setup-js/action.yaml
index f48956aba..b257d37d6 100644
--- a/.github/actions/setup-js/action.yaml
+++ b/.github/actions/setup-js/action.yaml
@@ -1,7 +1,7 @@
 name: Set up JavaScript workspace
 description: >-
-  Install pnpm and an official Node.js 26 build, prove that it has native
-  Temporal, and install the locked dependencies of the workspace in `js/`.
+  Install pnpm and an official Node.js build, then install the locked
+  dependencies of the workspace in `js/`.
 
 inputs:
   node-version:
@@ -23,13 +23,9 @@ runs:
         node-version: ${{ inputs.node-version }}
         node-version-file: ${{ inputs.node-version == '' && 'js/.node-version' || '' }}
 
-    # Official Node.js 26 binaries enable Temporal; some builds from source do
-    # not, and River refuses to run without it.
-    - name: Require native Temporal
+    - name: Report Node.js version
       shell: bash
-      run: |
-        node --version
-        test "$(node -p 'typeof Temporal')" = object
+      run: node --version
 
     - run: pnpm install --frozen-lockfile
       shell: bash
diff --git a/.github/workflows/js.yaml b/.github/workflows/js.yaml
index af5306e28..dab55a710 100644
--- a/.github/workflows/js.yaml
+++ b/.github/workflows/js.yaml
@@ -30,9 +30,8 @@ concurrency:
 permissions:
   contents: read
 
-# The full runtime deliberately requires native Temporal from Node 26. Every
-# job installs the official build selected by js/.node-version (or the matrix)
-# and asserts `typeof Temporal` before doing anything else.
+# Node 24 exercises the Temporal polyfill; Node 26 exercises native Temporal.
+# Jobs use js/.node-version unless a matrix selects a different release.
 
 defaults:
   run:
@@ -90,10 +89,15 @@ jobs:
       - run: pnpm run license:check
 
   packages:
-    name: Package archives
+    name: Package archives (Node ${{ matrix.node-version || 'from .node-version' }})
     runs-on: ubuntu-latest
     timeout-minutes: 20
 
+    strategy:
+      fail-fast: false
+      matrix:
+        node-version: ["24", ""]
+
     # The packed `node:test` suite runs its Postgres tests against this
     # database, and RIVER_REQUIRE_POSTGRES makes them fail instead of skip
     # when DATABASE_URL is missing.
@@ -121,6 +125,8 @@ jobs:
           persist-credentials: false
 
       - uses: ./.github/actions/setup-js
+        with:
+          node-version: ${{ matrix.node-version }}
 
       - run: pnpm run build:all
 
@@ -172,8 +178,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        # The minimum supported release and the current Node 26 release.
-        node-version: ["26.0.0", ""]
+        # Current releases for both supported Node lines.
+        node-version: ["24", ""]
 
     steps:
       - uses: actions/checkout@v7
@@ -200,7 +206,7 @@ jobs:
       - run: pnpm run test
 
   test_integration:
-    name: Test (integration, Postgres ${{ matrix.postgres-version }})
+    name: Test (integration, Node ${{ matrix.node-version || 'from .node-version' }}, Postgres ${{ matrix.postgres-version }})
     runs-on: ubuntu-latest
     timeout-minutes: 20
 
@@ -208,6 +214,10 @@ jobs:
       fail-fast: false
       matrix:
         postgres-version: [14, 15, 16, 17, 18]
+        node-version: [""]
+        include:
+          - node-version: "24"
+            postgres-version: 18
 
     services:
       postgres:
@@ -232,6 +242,8 @@ jobs:
           persist-credentials: false
 
       - uses: ./.github/actions/setup-js
+        with:
+          node-version: ${{ matrix.node-version }}
 
       - run: pnpm run build:all
 
diff --git a/Makefile b/Makefile
index a3c116d43..4c9f13ab6 100644
--- a/Makefile
+++ b/Makefile
@@ -132,7 +132,7 @@ lint/java/tools: ## Lint Java's Go maintenance tools
 	golangci-lint run --fix ./java/bin/sync-migrations/*.go
 
 # JavaScript targets, like the Rust ones, are separate from `lint` and `test`
-# and need Node.js 26 and pnpm; they delegate to the workspace's own scripts.
+# and need Node.js 24 or newer and pnpm; they delegate to the workspace's own scripts.
 # Run `pnpm -C js install` first.
 .PHONY: build/js
 build/js: ## Build every JavaScript package
diff --git a/js/CHANGELOG.md b/js/CHANGELOG.md
index b747fd449..a94f7c92d 100644
--- a/js/CHANGELOG.md
+++ b/js/CHANGELOG.md
@@ -7,6 +7,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Support Node.js 24 across all packages. River automatically installs a `Temporal` polyfill when the runtime has no native implementation, preserving native `Temporal` on Node.js 26.
+
+### Fixed
+
+- Worker threads respect cancellation received while loading a handler module, before invoking its handler.
+
 ## [0.2.0] - 2026-10-07
 
 ### Added
diff --git a/js/README.md b/js/README.md
index 7d8f0773c..3e0f35037 100644
--- a/js/README.md
+++ b/js/README.md
@@ -7,21 +7,17 @@ the same jobs in the same database.
 
 ## Requirements
 
-- **Node.js 26 with native `Temporal`.** River uses `Temporal.Instant` for
+- **Node.js 24 or newer.** River uses `Temporal.Instant` for
   timestamps and `bigint` for IDs, so no value read from the database is lost.
-  Official Node.js 26 builds (nodejs.org, `actions/setup-node`, the official
-  Docker images) enable Temporal. Some distribution and Homebrew builds do
-  not; check with:
-
-  ```sh
-  node -p "typeof Temporal" # must print "object"
-  ```
-
+  Importing River automatically installs
+  [`@js-temporal/polyfill`](https://github.com/js-temporal/temporal-polyfill)
+  globally when `Temporal` is absent, including in worker threads. Node.js 26
+  uses its native implementation. No extra imports or runtime flags are needed.
 - **TypeScript 6.0 or newer**, if you use TypeScript. Install `@types/node`
-  26 or newer (and `@types/pg` with `@riverqueue/driver-pg`) and list `"node"`
+  24 or newer (and `@types/pg` with `@riverqueue/driver-pg`) and list `"node"`
   in `compilerOptions.types`. JavaScript users need neither.
 - **ESM.** The packages ship one ES module build. CommonJS code can
-  `require()` them on Node 26, which returns the same module instance as
+  `require()` them on Node 24 or newer, which returns the same module instance as
   `import`; TypeScript CommonJS projects need `module: "node20"` or
   `"nodenext"`.
 
diff --git a/js/cli/README.md b/js/cli/README.md
index 32542c34a..126aa4985 100644
--- a/js/cli/README.md
+++ b/js/cli/README.md
@@ -2,7 +2,7 @@
 
 The `riverqueue` command runs River's database migrations and a throughput
 benchmark, and upgrades code written for `riverqueue@0.1`. It requires
-Node.js 26 or newer and mirrors the commands of River's Go CLI.
+Node.js 24 or newer and mirrors the commands of River's Go CLI.
 
 ```sh
 npm install --save-dev @riverqueue/cli
@@ -142,9 +142,9 @@ process.exitCode = await run(process.argv.slice(2), {
 
 ## Requirements
 
-Node.js 26 or newer with native `Temporal`: `node -p "typeof Temporal"` must
-print `object`. Official Node.js binaries include it; some builds compiled from
-source, including some distribution and Homebrew packages, do not.
+Node.js 24 or newer. River automatically installs a global `Temporal`
+polyfill when the runtime has no native implementation; Node.js 26 uses
+native `Temporal`.
 
 The CLI installs its own matching `riverqueue` and database packages.
 
diff --git a/js/cli/package.json b/js/cli/package.json
index 2b61dd6de..96915fcfc 100644
--- a/js/cli/package.json
+++ b/js/cli/package.json
@@ -7,7 +7,7 @@
     "./dist/bin.js"
   ],
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "bin": {
     "riverqueue": "./dist/bin.js"
@@ -55,7 +55,7 @@
     "riverqueue": "workspace:0.2.0"
   },
   "peerDependencies": {
-    "@types/node": ">=26",
+    "@types/node": ">=24",
     "@types/pg": ">=8",
     "typescript": "^5.0.0 || ^6.0.0"
   },
diff --git a/js/docs/development.md b/js/docs/development.md
index d0b951162..eb9a28c44 100644
--- a/js/docs/development.md
+++ b/js/docs/development.md
@@ -7,15 +7,12 @@ Go and Rust implementations. Run the `pnpm` commands below from `js/`, or use
 River's top-level `make` targets (`make lint/js`, `make test/js`, and so on),
 which delegate to `pnpm -C js`.
 
-Use an official Node.js 26 build, which includes native Temporal. The
-workspace's `.node-version` selects Node 26 for version managers such as fnm,
-nvm (`nvm use $(cat .node-version)`), and `actions/setup-node`. Some Node.js
-builds compiled from source, including some distribution and Homebrew
-packages, lack Temporal, and most unit tests then fail with
-`ReferenceError: Temporal is not defined`. Check before installing, then use
-the pnpm version pinned by `packageManager` in `package.json`:
-
-    node -p "typeof Temporal"   # must print "object"
+Use Node.js 24 or newer. The workspace's `.node-version` selects Node 26 for
+version managers such as fnm, nvm (`nvm use $(cat .node-version)`), and
+`actions/setup-node`. River installs a global Temporal polyfill when the
+runtime has no native implementation; the tests use the same initialization.
+Use the pnpm version pinned by `packageManager` in `package.json`:
+
     pnpm install
 
 TypeScript 6.0 is the minimum compiler for the published declarations, which
@@ -190,13 +187,13 @@ to benchmark against a disposable database:
 
 River's `.github/workflows/js.yaml` runs on pull requests and pushes to
 `master` that change `js/`, River's migrations or SQL, or the workflow itself,
-and on `js/v*` release tags. Each job installs the official Node.js build from
-`js/.node-version` and fails unless `typeof Temporal` is `object`. The jobs
+and on `js/v*` release tags. Each job installs an official Node.js build from
+`js/.node-version` or its version matrix. The jobs
 cover build, both type-check lanes, generated migrations (compared with
 River's sources), API reports, TypeDoc, README snippets, the 0.1 fixture, lint,
-formatting, licenses, packed archives and examples, unit tests on Node 26.0.0
-and the current Node 26 release, and integration tests on Postgres 14
-through 18.
+formatting, licenses, packed archives and examples. Unit tests and packed
+packages run on supported Node.js versions. Package tests include CommonJS
+and TypeScript consumers. Integration tests cover supported Postgres versions.
 
 Unit tests compare unique keys, protocol values, notification dispatch,
 retry timing, cron schedules, and snooze counting with fixtures that
diff --git a/js/docs/migrating-from-0.1.md b/js/docs/migrating-from-0.1.md
index 3887c454a..f59a06241 100644
--- a/js/docs/migrating-from-0.1.md
+++ b/js/docs/migrating-from-0.1.md
@@ -7,9 +7,9 @@ that still needs attention.
 
 ## Runtime requirements
 
-The package needs Node.js 26 with native `Temporal` and ships as ESM; see
-[requirements](../README.md#requirements). There is no second CommonJS build
-and no `Temporal` polyfill.
+The package needs Node.js 24 or newer and ships as ESM; see
+[requirements](../README.md#requirements). River automatically installs a
+global `Temporal` polyfill when the runtime has no native implementation.
 
 ## Codemod
 
diff --git a/js/driver/pg/README.md b/js/driver/pg/README.md
index 792c66989..8f64ff791 100644
--- a/js/driver/pg/README.md
+++ b/js/driver/pg/README.md
@@ -1,6 +1,6 @@
 # `@riverqueue/driver-pg`
 
-This package is River's complete Postgres backend for Node.js 26 and newer.
+This package is River's complete Postgres backend for Node.js 24 and newer.
 It accepts a caller-owned `pg.Pool`, performs insertion and runtime operations,
 and implements notifications, leadership, maintenance, and queue control.
 
@@ -94,9 +94,9 @@ driver, migrator, and CLI. Never interpolate an untrusted schema name.
 
 ## Requirements
 
-Node.js 26 or newer with native `Temporal`: `node -p "typeof Temporal"` must
-print `object`. Official Node.js binaries include it; some builds compiled from
-source, including some distribution and Homebrew packages, do not.
+Node.js 24 or newer. River automatically installs a global `Temporal`
+polyfill when the runtime has no native implementation; Node.js 26 uses
+native `Temporal`.
 
 Install `riverqueue` at exactly this package's version. It is a peer dependency,
 so npm rejects a mismatched pair instead of loading two copies.
diff --git a/js/driver/pg/package.json b/js/driver/pg/package.json
index 5927888d9..542f2d529 100644
--- a/js/driver/pg/package.json
+++ b/js/driver/pg/package.json
@@ -14,7 +14,7 @@
     }
   },
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "files": [
     "dist",
diff --git a/js/driver/prisma/README.md b/js/driver/prisma/README.md
index 469f124b0..10beff902 100644
--- a/js/driver/prisma/README.md
+++ b/js/driver/prisma/README.md
@@ -78,9 +78,9 @@ JavaScript's safe range in arguments or metadata stay exact.
 
 ## Requirements
 
-Node.js 26 or newer with native `Temporal`: `node -p "typeof Temporal"` must
-print `object`. Official Node.js binaries include it; some builds compiled from
-source, including some distribution and Homebrew packages, do not.
+Node.js 24 or newer. River automatically installs a global `Temporal`
+polyfill when the runtime has no native implementation; Node.js 26 uses
+native `Temporal`.
 
 Install `riverqueue` at exactly this package's version. It is a peer dependency,
 so npm rejects a mismatched pair instead of loading two copies.
diff --git a/js/driver/prisma/package.json b/js/driver/prisma/package.json
index 5d1684ef0..ae88e4608 100644
--- a/js/driver/prisma/package.json
+++ b/js/driver/prisma/package.json
@@ -14,7 +14,7 @@
     }
   },
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "files": [
     "dist",
diff --git a/js/driver/sqlite/README.md b/js/driver/sqlite/README.md
index c6f781180..283b637f9 100644
--- a/js/driver/sqlite/README.md
+++ b/js/driver/sqlite/README.md
@@ -1,6 +1,6 @@
 # `@riverqueue/driver-sqlite`
 
-This package is River's preview SQLite backend for Node 26 and newer. It uses
+This package is River's preview SQLite backend for Node 24 and newer. It uses
 the built-in synchronous `node:sqlite` API.
 
 Apply River's generated canonical migrations explicitly before constructing a
@@ -241,9 +241,9 @@ listeners once per job.
 
 ## Requirements
 
-Node.js 26 or newer with native `Temporal`: `node -p "typeof Temporal"` must
-print `object`. Official Node.js binaries include it; some builds compiled from
-source, including some distribution and Homebrew packages, do not.
+Node.js 24 or newer. River automatically installs a global `Temporal`
+polyfill when the runtime has no native implementation; Node.js 26 uses
+native `Temporal`.
 
 Install `riverqueue` at exactly this package's version. It is a peer dependency,
 so npm rejects a mismatched pair instead of loading two copies.
diff --git a/js/driver/sqlite/package.json b/js/driver/sqlite/package.json
index 1a88031b5..3f291ca68 100644
--- a/js/driver/sqlite/package.json
+++ b/js/driver/sqlite/package.json
@@ -5,7 +5,7 @@
   "type": "module",
   "sideEffects": false,
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "main": "./dist/index.js",
   "types": "./dist/index.d.ts",
@@ -45,7 +45,7 @@
     "provenance": true
   },
   "peerDependencies": {
-    "@types/node": ">=26",
+    "@types/node": ">=24",
     "riverqueue": "workspace:0.2.0"
   },
   "peerDependenciesMeta": {
diff --git a/js/etc/riverqueue.api.md b/js/etc/riverqueue.api.md
index d4f3b693e..92e2cf195 100644
--- a/js/etc/riverqueue.api.md
+++ b/js/etc/riverqueue.api.md
@@ -12,9 +12,9 @@ declarations, and file layout are omitted.
 /**
  * Verify the runtime features River relies on before database work begins.
  *
- * Official Node.js 26 builds expose Temporal by default. This explicit check
- * gives custom builds and unsupported runtimes a useful failure instead of a
- * later `ReferenceError` or a lossy timestamp fallback.
+ * River provides a Temporal polyfill when the runtime has no native
+ * implementation. This check gives unsupported runtimes a useful failure
+ * instead of a later `ReferenceError` or a lossy timestamp fallback.
  */
 export declare function assertRuntimeSupport(): void;
 ```
diff --git a/js/examples/graceful-shutdown/package.json b/js/examples/graceful-shutdown/package.json
index 3767ce26c..0baf4fe17 100644
--- a/js/examples/graceful-shutdown/package.json
+++ b/js/examples/graceful-shutdown/package.json
@@ -4,7 +4,7 @@
   "private": true,
   "type": "module",
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "scripts": {
     "build": "tsc",
diff --git a/js/examples/hooks-metrics/package.json b/js/examples/hooks-metrics/package.json
index 3b0602ab0..74f67ada6 100644
--- a/js/examples/hooks-metrics/package.json
+++ b/js/examples/hooks-metrics/package.json
@@ -4,7 +4,7 @@
   "private": true,
   "type": "module",
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "scripts": {
     "build": "tsc",
diff --git a/js/examples/mixed-language/package.json b/js/examples/mixed-language/package.json
index c24c1826e..9b2dbac67 100644
--- a/js/examples/mixed-language/package.json
+++ b/js/examples/mixed-language/package.json
@@ -4,7 +4,7 @@
   "private": true,
   "type": "module",
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "scripts": {
     "build": "tsc",
diff --git a/js/examples/node-postgres/package.json b/js/examples/node-postgres/package.json
index 2434a10e0..546f67cbc 100644
--- a/js/examples/node-postgres/package.json
+++ b/js/examples/node-postgres/package.json
@@ -4,7 +4,7 @@
   "private": true,
   "type": "module",
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "scripts": {
     "build": "tsc",
diff --git a/js/examples/pg-worker/package.json b/js/examples/pg-worker/package.json
index ff2fca531..6545b2cae 100644
--- a/js/examples/pg-worker/package.json
+++ b/js/examples/pg-worker/package.json
@@ -4,7 +4,7 @@
   "private": true,
   "type": "module",
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "scripts": {
     "build": "tsc",
diff --git a/js/examples/prisma/package.json b/js/examples/prisma/package.json
index 35af42adc..af67caa8c 100644
--- a/js/examples/prisma/package.json
+++ b/js/examples/prisma/package.json
@@ -4,7 +4,7 @@
   "private": true,
   "type": "module",
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "scripts": {
     "generate": "prisma generate",
diff --git a/js/examples/sqlite-worker/README.md b/js/examples/sqlite-worker/README.md
index 92cff0030..192d4f773 100644
--- a/js/examples/sqlite-worker/README.md
+++ b/js/examples/sqlite-worker/README.md
@@ -2,7 +2,7 @@
 
 This example applies River's SQLite migrations to an in-memory database,
 inserts a typed job, works it in-process, observes its committed completion,
-and shuts down cleanly. It needs only Node.js 26 and the workspace packages.
+and shuts down cleanly. It needs only Node.js 24 and the workspace packages.
 
 From the repository root:
 
diff --git a/js/examples/sqlite-worker/package.json b/js/examples/sqlite-worker/package.json
index 8b4c5c860..b83c615a6 100644
--- a/js/examples/sqlite-worker/package.json
+++ b/js/examples/sqlite-worker/package.json
@@ -4,7 +4,7 @@
   "private": true,
   "type": "module",
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "scripts": {
     "build": "tsc",
diff --git a/js/examples/worker-thread-cpu/package.json b/js/examples/worker-thread-cpu/package.json
index 28125e35c..bf4f3ac0e 100644
--- a/js/examples/worker-thread-cpu/package.json
+++ b/js/examples/worker-thread-cpu/package.json
@@ -4,7 +4,7 @@
   "private": true,
   "type": "module",
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "scripts": {
     "build": "tsc",
diff --git a/js/migrate/README.md b/js/migrate/README.md
index 25a3ae3f0..81b0bd015 100644
--- a/js/migrate/README.md
+++ b/js/migrate/README.md
@@ -1,7 +1,7 @@
 # `@riverqueue/migrate`
 
 River's Postgres and SQLite migrations, with a runner that applies them.
-Requires Node.js 26 or newer.
+Requires Node.js 24 or newer.
 
 River never migrates on its own: clients don't touch the schema when they are
 constructed or started. Run migrations as a deployment step, either with this
@@ -119,9 +119,9 @@ checked for drift, so don't edit it by hand.
 
 ## Requirements
 
-Node.js 26 or newer with native `Temporal`: `node -p "typeof Temporal"` must
-print `object`. Official Node.js binaries include it; some builds compiled from
-source, including some distribution and Homebrew packages, do not.
+Node.js 24 or newer. River automatically installs a global `Temporal`
+polyfill when the runtime has no native implementation; Node.js 26 uses
+native `Temporal`.
 
 Install `riverqueue` at exactly this package's version. It is a peer dependency,
 so npm rejects a mismatched pair instead of loading two copies.
diff --git a/js/migrate/package.json b/js/migrate/package.json
index 3bf4090a5..c8294eef9 100644
--- a/js/migrate/package.json
+++ b/js/migrate/package.json
@@ -5,7 +5,7 @@
   "type": "module",
   "sideEffects": false,
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "main": "./dist/index.js",
   "types": "./dist/index.d.ts",
@@ -45,7 +45,7 @@
     "provenance": true
   },
   "peerDependencies": {
-    "@types/node": ">=26",
+    "@types/node": ">=24",
     "riverqueue": "workspace:0.2.0"
   },
   "peerDependenciesMeta": {
diff --git a/js/package.json b/js/package.json
index 1b8ef963a..a617dfbff 100644
--- a/js/package.json
+++ b/js/package.json
@@ -3,7 +3,14 @@
   "version": "0.2.0",
   "description": "TypeScript implementation of River, a fast and reliable background job system.",
   "type": "module",
-  "sideEffects": false,
+  "sideEffects": [
+    "./dist/index.js",
+    "./dist/unstable-driver.js",
+    "./dist/internal/temporal.js",
+    "./src/index.ts",
+    "./src/unstable-driver.ts",
+    "./src/internal/temporal.ts"
+  ],
   "main": "./dist/index.js",
   "types": "./dist/index.d.ts",
   "exports": {
@@ -19,7 +26,7 @@
     }
   },
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "files": [
     "dist",
@@ -72,8 +79,11 @@
     "access": "public",
     "provenance": true
   },
+  "dependencies": {
+    "@js-temporal/polyfill": "^0.5.1"
+  },
   "peerDependencies": {
-    "@types/node": ">=26"
+    "@types/node": ">=24"
   },
   "peerDependenciesMeta": {
     "@types/node": {
diff --git a/js/pnpm-lock.yaml b/js/pnpm-lock.yaml
index fa5c8f39c..742e4fed1 100644
--- a/js/pnpm-lock.yaml
+++ b/js/pnpm-lock.yaml
@@ -14,6 +14,10 @@ overrides:
 importers:
 
   .:
+    dependencies:
+      '@js-temporal/polyfill':
+        specifier: ^0.5.1
+        version: 0.5.1
     devDependencies:
       '@arethetypeswrong/cli':
         specifier: ^0.18.5
@@ -546,6 +550,10 @@ packages:
   '@jridgewell/trace-mapping@0.3.31':
     resolution: {integrity: sha512-zzNR+SdQSDJzc8joaeP8QQoCQr8NuYx2dIIytl1QeBEZHJ9uW6hebsrYgbz8hJwUQao3TWCMtmfV8Nu1twOLAw==}
 
+  '@js-temporal/polyfill@0.5.1':
+    resolution: {integrity: sha512-hloP58zRVCRSpgDxmqCWJNlizAlUgJFqG2ypq79DCvyv9tHjRYMDOcPFjzfl/A1/YxDvRCZz8wvZvmapQnKwFQ==}
+    engines: {node: '>=12'}
+
   '@loaderkit/resolve@1.0.6':
     resolution: {integrity: sha512-G8FdIoF5CypfwmD9rl8BXod5HDn8JqB0CCNBXDTaRZ+yRYhARrrSToX1zg1zy9jX3zLqigsELwhT4gNtkdQAUg==}
 
@@ -1939,6 +1947,9 @@ packages:
   js-tokens@10.0.0:
     resolution: {integrity: sha512-lM/UBzQmfJRo9ABXbPWemivdCW8V2G8FHaHdypQaIy523snUjog0W71ayWXTjiR+ixeMyVHN2XcpnTd/liPg/Q==}
 
+  jsbi@4.3.2:
+    resolution: {integrity: sha512-9fqMSQbhJykSeii05nxKl4m6Eqn2P6rOlYiS+C5Dr/HPIU/7yZxu5qzbs40tgaFORiw2Amd0mirjxatXYMkIew==}
+
   json-buffer@3.0.1:
     resolution: {integrity: sha512-4bV5BfR2mqfQTJm+V5tPPdf+ZpuhiIvTuAB5g8kcrXOZpTT/QwwVRWBywX1ozr6lEuPdbHxwaJlm9G6mI2sfSQ==}
 
@@ -3114,6 +3125,10 @@ snapshots:
       '@jridgewell/resolve-uri': 3.1.2
       '@jridgewell/sourcemap-codec': 1.5.5
 
+  '@js-temporal/polyfill@0.5.1':
+    dependencies:
+      jsbi: 4.3.2
+
   '@loaderkit/resolve@1.0.6':
     dependencies:
       '@braidai/lang': 1.1.2
@@ -4491,6 +4506,8 @@ snapshots:
 
   js-tokens@10.0.0: {}
 
+  jsbi@4.3.2: {}
+
   json-buffer@3.0.1: {}
 
   json-parse-even-better-errors@5.0.0: {}
diff --git a/js/scripts/check-packages.mjs b/js/scripts/check-packages.mjs
index f2ff305b2..d97cbf098 100644
--- a/js/scripts/check-packages.mjs
+++ b/js/scripts/check-packages.mjs
@@ -17,6 +17,8 @@ import process from "node:process";
 import { fileURLToPath } from "node:url";
 import { promisify } from "node:util";
 
+import { build as buildWithVite } from "vite";
+
 import {
   assertNoDeniedContent,
   assertPortableArchivePath,
@@ -165,7 +167,7 @@ async function inspectArchive(packageSpec, archivePath) {
     `${packageSpec.name} packages the canonical MPL-2.0 text`
   );
   assert.equal(packageJson.license, "MPL-2.0");
-  assert.equal(packageJson.engines?.node, ">=26");
+  assert.equal(packageJson.engines?.node, ">=24");
   assert.equal(packageJson.publishConfig?.access, "public");
   assert.equal(packageJson.publishConfig?.provenance, true);
   assert.equal(packageJson.authors, undefined, "`authors` is not an npm field");
@@ -415,6 +417,32 @@ if (typeof parsed !== "object" || parsed === null || Array.isArray(parsed) ||
   );
   await run(process.execPath, [join(consumerDirectory, "import.mjs")]);
 
+  // A bundler must retain Temporal initialization even when most exports
+  // are unused. Exercise the published sideEffects metadata on Node 24 too.
+  await writeFile(
+    join(consumerDirectory, "bundle-entry.mjs"),
+    `import { cron } from "riverqueue";
+const start = Temporal.Instant.from("2026-10-11T12:34:56Z");
+if (cron("@every 1s").next(start).toString() !== "2026-10-11T12:34:57Z") {
+  throw new Error("bundled River did not initialize Temporal");
+}
+`
+  );
+  await buildWithVite({
+    build: {
+      outDir: "bundled",
+      ssr: join(consumerDirectory, "bundle-entry.mjs"),
+      target: "node24",
+    },
+    configFile: false,
+    logLevel: "error",
+    root: consumerDirectory,
+    ssr: { noExternal: ["riverqueue", "@js-temporal/polyfill", "jsbi"] },
+  });
+  await run(process.execPath, [
+    join(consumerDirectory, "bundled", "bundle-entry.js"),
+  ]);
+
   await writeFile(
     join(consumerDirectory, "require.cjs"),
     `
@@ -703,7 +731,8 @@ void [workers, exactNumber, uniqueStates, insertion, pgInsertion, sqliteInsertio
   await npmInstall(consumerDirectory, [
     "--save-dev",
     ...["@types/node", "@types/pg"].map(
-      (name) => `${name}@${rootPackageJson.devDependencies[name]}`
+      (name) =>
+        `${name}@${name === "@types/node" ? "^24" : rootPackageJson.devDependencies[name]}`
     ),
   ]);
   for (const compilerPackage of ["typescript", "typescript-next"]) {
@@ -721,7 +750,7 @@ void [workers, exactNumber, uniqueStates, insertion, pgInsertion, sqliteInsertio
   await verifyCommonJsTypeScriptConsumer(consumerDirectory);
 }
 
-// The packages are ESM-only. Node 26 loads them from CommonJS through
+// The packages are ESM-only. Node 24 and newer load them from CommonJS through
 // `require(esm)`, and TypeScript models that only for `module: node20` and
 // `nodenext`; `node16` and `node18` report TS1479, which is what Are The Types
 // Wrong's `cjs-resolves-to-esm` rule flags. Compile a CommonJS consumer in the
diff --git a/js/scripts/packed-tests/packages.test.mjs b/js/scripts/packed-tests/packages.test.mjs
index 594a79a3d..c6489d870 100644
--- a/js/scripts/packed-tests/packages.test.mjs
+++ b/js/scripts/packed-tests/packages.test.mjs
@@ -29,6 +29,32 @@ const SATELLITES = [
 ];
 
 describe("packed package graph", () => {
+  it("initializes Temporal from every entry point and preserves native constructors", async () => {
+    for (const name of [
+      "riverqueue",
+      "riverqueue/unstable-driver",
+      ...SATELLITES,
+    ]) {
+      await execFileAsync(
+        process.execPath,
+        [
+          "--input-type=module",
+          "-e",
+          `import assert from "node:assert/strict";
+const original = globalThis.Temporal;
+await import(${JSON.stringify(name)});
+assert.equal(typeof Temporal, "object");
+if (original) assert.equal(Temporal, original);
+const instant = Temporal.Instant.from("2026-10-11T12:34:56.123456789Z");
+assert.equal(instant.toString(), "2026-10-11T12:34:56.123456789Z");
+assert.equal(Temporal.Duration.from({ seconds: 2 }).total("milliseconds"), 2000);
+`,
+        ],
+        { cwd: consumerDirectory }
+      );
+    }
+  });
+
   it("resolves exactly one riverqueue from every satellite package", () => {
     const root = require.resolve("riverqueue");
     for (const name of SATELLITES) {
diff --git a/js/scripts/vitest-setup.mjs b/js/scripts/vitest-setup.mjs
index 44af8d667..72fdfb91d 100644
--- a/js/scripts/vitest-setup.mjs
+++ b/js/scripts/vitest-setup.mjs
@@ -13,6 +13,10 @@ import {
 import fc from "fast-check";
 import { afterAll, afterEach, beforeAll } from "vitest";
 
+// Tests also import internal modules directly, bypassing the public entries
+// that initialize Temporal for applications.
+import "../src/internal/temporal.ts";
+
 // Property tests are deterministic by default. Set FAST_CHECK_SEED to an
 // integer to replay a reported failure or explore another region of the
 // input space; FAST_CHECK_SEED=random picks a fresh seed per run. fast-check
diff --git a/js/src/cron.property.test.ts b/js/src/cron.property.test.ts
index 3c978059e..dc913db52 100644
--- a/js/src/cron.property.test.ts
+++ b/js/src/cron.property.test.ts
@@ -108,7 +108,8 @@ const instant = fc
   .bigInt({ max: 2_208_988_800_000_000_000n, min: 946_684_800_000_000_000n })
   .map((nanoseconds) => Temporal.Instant.fromEpochNanoseconds(nanoseconds));
 
-describe("cron properties", () => {
+// The Temporal polyfill on Node 24 needs more time for 300 cases on CI runners.
+describe("cron properties", { timeout: 30_000 }, () => {
   it("returns strictly increasing whole-second occurrences", () => {
     fc.assert(
       fc.property(
diff --git a/js/src/index.ts b/js/src/index.ts
index ed04a2d6d..39e6bcdbf 100644
--- a/js/src/index.ts
+++ b/js/src/index.ts
@@ -2,6 +2,8 @@
 // The public declarations use the global `Temporal` types. The preserved
 // reference loads them for TypeScript consumers without a `lib` setting.
 
+import "./internal/temporal.js";
+
 export { Client } from "./client.js";
 export type {
   CheckedInsertManyItems,
diff --git a/js/src/internal/temporal.ts b/js/src/internal/temporal.ts
new file mode 100644
index 000000000..b0b5f0c58
--- /dev/null
+++ b/js/src/internal/temporal.ts
@@ -0,0 +1,13 @@
+// Node 24 needs a polyfill; Node 26 keeps its native implementation. Install
+// it before evaluating River modules so applications can use the same global
+// Temporal constructors as River, including inside worker threads.
+import { Temporal } from "@js-temporal/polyfill";
+
+const nativeTemporal: unknown = Reflect.get(globalThis, "Temporal");
+if (nativeTemporal === undefined) {
+  Object.defineProperty(globalThis, "Temporal", {
+    configurable: true,
+    value: Temporal,
+    writable: true,
+  });
+}
diff --git a/js/src/runtime-support.test.ts b/js/src/runtime-support.test.ts
index 68dd37241..09761d9e9 100644
--- a/js/src/runtime-support.test.ts
+++ b/js/src/runtime-support.test.ts
@@ -8,19 +8,30 @@ describe("assertRuntimeSupport", () => {
     vi.unstubAllGlobals();
   });
 
-  it("accepts the supported Node runtime and native Temporal implementation", () => {
+  it("accepts the supported Node runtime and Temporal implementation", () => {
     expect(() => assertRuntimeSupport()).not.toThrow();
     expect(
       Temporal.Instant.from("2026-08-30T18:00:00.123456Z").toString()
     ).toBe("2026-08-30T18:00:00.123456Z");
   });
 
-  it("points runtimes without native Temporal at the requirements", () => {
+  it("points runtimes without Temporal at the requirements", () => {
     vi.stubGlobal("Temporal", undefined);
 
     expect(() => assertRuntimeSupport()).toThrow(ConfigurationError);
     expect(() => assertRuntimeSupport()).toThrow(
-      /native Temporal API.*typeof Temporal.*river\/tree\/master\/js#requirements/u
+      /Temporal API.*river\/tree\/master\/js#requirements/u
+    );
+  });
+
+  it("rejects Node versions older than 24", () => {
+    vi.stubGlobal("process", {
+      ...process,
+      versions: { ...process.versions, node: "22.0.0" },
+    });
+
+    expect(() => assertRuntimeSupport()).toThrow(
+      /requires Node.js 24 or newer; found 22.0.0/u
     );
   });
 });
diff --git a/js/src/runtime-support.ts b/js/src/runtime-support.ts
index eb63b0230..eaeea853e 100644
--- a/js/src/runtime-support.ts
+++ b/js/src/runtime-support.ts
@@ -1,3 +1,5 @@
+import "./internal/temporal.js";
+
 import { ConfigurationError } from "./errors.js";
 
 const REQUIREMENTS_URL =
@@ -6,15 +8,15 @@ const REQUIREMENTS_URL =
 /**
  * Verify the runtime features River relies on before database work begins.
  *
- * Official Node.js 26 builds expose Temporal by default. This explicit check
- * gives custom builds and unsupported runtimes a useful failure instead of a
- * later `ReferenceError` or a lossy timestamp fallback.
+ * River provides a Temporal polyfill when the runtime has no native
+ * implementation. This check gives unsupported runtimes a useful failure
+ * instead of a later `ReferenceError` or a lossy timestamp fallback.
  */
 export function assertRuntimeSupport(): void {
   const major = Number.parseInt(process.versions.node.split(".")[0] ?? "", 10);
-  if (!Number.isSafeInteger(major) || major < 26) {
+  if (!Number.isSafeInteger(major) || major < 24) {
     throw new ConfigurationError(
-      `River requires Node.js 26 or newer; found ${process.versions.node} ` +
+      `River requires Node.js 24 or newer; found ${process.versions.node} ` +
         `(see ${REQUIREMENTS_URL})`
     );
   }
@@ -35,9 +37,8 @@ export function assertRuntimeSupport(): void {
     typeof temporal.Now?.instant !== "function"
   ) {
     throw new ConfigurationError(
-      "River requires a Node.js build with the native Temporal API enabled; " +
-        "official Node.js 26 binaries include it, but some builds compiled " +
-        'from source do not. `node -p "typeof Temporal"` must print "object" ' +
+      "River requires the Temporal API; keep the native implementation " +
+        "or the polyfill installed by River available on globalThis " +
         `(see ${REQUIREMENTS_URL})`
     );
   }
diff --git a/js/src/unstable-driver.ts b/js/src/unstable-driver.ts
index efb3133f6..d6176552a 100644
--- a/js/src/unstable-driver.ts
+++ b/js/src/unstable-driver.ts
@@ -2,6 +2,8 @@
 // The public declarations use the global `Temporal` types. The preserved
 // reference loads them for TypeScript consumers without a `lib` setting.
 
+import "./internal/temporal.js";
+
 /**
  * Explicitly unstable semantic SPI for first-party River backend packages.
  *
diff --git a/js/test/README.md b/js/test/README.md
index aa5d35b63..49bcf6c5d 100644
--- a/js/test/README.md
+++ b/js/test/README.md
@@ -94,9 +94,9 @@ external service and exercises the complete runtime.
 
 ## Requirements
 
-Node.js 26 or newer with native `Temporal`: `node -p "typeof Temporal"` must
-print `object`. Official Node.js binaries include it; some builds compiled from
-source, including some distribution and Homebrew packages, do not.
+Node.js 24 or newer. River automatically installs a global `Temporal`
+polyfill when the runtime has no native implementation; Node.js 26 uses
+native `Temporal`.
 
 Install `riverqueue` at exactly this package's version. It is a peer dependency,
 so npm rejects a mismatched pair instead of loading two copies.
diff --git a/js/test/package.json b/js/test/package.json
index 9c8c95649..bf2ab4ebe 100644
--- a/js/test/package.json
+++ b/js/test/package.json
@@ -14,7 +14,7 @@
     }
   },
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "files": [
     "dist",
diff --git a/js/worker-threads/README.md b/js/worker-threads/README.md
index 5ba56e997..3303b37d5 100644
--- a/js/worker-threads/README.md
+++ b/js/worker-threads/README.md
@@ -158,7 +158,7 @@ so an executor that is never closed does not prevent exit.
 
 ## TypeScript sources in development
 
-Node 26 strips TypeScript types natively, and River's threads load a module's
+Node 24 and newer strip TypeScript types natively, and River's threads load a module's
 TypeScript source when the `.js` file that a handler URL or one of its relative
 imports names does not exist but a `.ts` file beside it does. Keep referencing
 handler modules by their compiled `.js` name, as above; the same URL then
@@ -184,9 +184,9 @@ run trusted handler modules.
 
 ## Requirements
 
-Node.js 26 or newer with native `Temporal`: `node -p "typeof Temporal"` must
-print `object`. Official Node.js binaries include it; some builds compiled from
-source, including some distribution and Homebrew packages, do not.
+Node.js 24 or newer. River automatically installs a global `Temporal`
+polyfill when the runtime has no native implementation; Node.js 26 uses
+native `Temporal`.
 
 Install `riverqueue` at exactly this package's version. It is a peer dependency,
 so npm rejects a mismatched pair instead of loading two copies.
diff --git a/js/worker-threads/package.json b/js/worker-threads/package.json
index a86c99865..8e3fb62d9 100644
--- a/js/worker-threads/package.json
+++ b/js/worker-threads/package.json
@@ -16,7 +16,7 @@
     }
   },
   "engines": {
-    "node": ">=26"
+    "node": ">=24"
   },
   "files": [
     "dist",
@@ -47,7 +47,7 @@
     "provenance": true
   },
   "peerDependencies": {
-    "@types/node": ">=26",
+    "@types/node": ">=24",
     "riverqueue": "workspace:0.2.0"
   },
   "peerDependenciesMeta": {
diff --git a/js/worker-threads/src/client.test.ts b/js/worker-threads/src/client.test.ts
index 8fc91ec09..a281ccca3 100644
--- a/js/worker-threads/src/client.test.ts
+++ b/js/worker-threads/src/client.test.ts
@@ -4,6 +4,7 @@ import { SqliteDriver } from "@riverqueue/driver-sqlite";
 import { createMigrator } from "@riverqueue/migrate";
 import {
   Client,
+  consoleLogger,
   exactJsonNumber,
   isExactJsonNumber,
   LifecycleError,
@@ -38,6 +39,7 @@ describe("WorkerThreads with River clients", () => {
   interface TestClient {
     readonly client: Client;
     readonly driver: SqliteDriver;
+    readonly started: Promise<void>;
   }
 
   const setup = async (
@@ -56,8 +58,15 @@ describe("WorkerThreads with River clients", () => {
       testJob,
       executor.handler(testJob, { exportName, module: handlers })
     );
+    const started = Promise.withResolvers<undefined>();
     const client = new Client(driver, {
       ...(jobStuckThreshold === undefined ? {} : { jobStuckThreshold }),
+      logger: {
+        ...consoleLogger,
+        info: (_attributes, message) => {
+          if (message === "started") started.resolve(undefined);
+        },
+      },
       queues: {
         default: {
           fetchCooldown: { milliseconds: 1 },
@@ -67,7 +76,7 @@ describe("WorkerThreads with River clients", () => {
       },
       workers,
     });
-    return { client, driver };
+    return { client, driver, started: started.promise };
   };
 
   it("closes an executor at the end of an await using scope", async () => {
@@ -97,11 +106,11 @@ describe("WorkerThreads with River clients", () => {
 
   it("cancels a cooperative handler and reuses its thread", async () => {
     await using executor = new WorkerThreads({ maxThreads: 1 });
-    const { client, driver } = await setup(executor, "cooperate");
+    const { client, driver, started } = await setup(executor, "cooperate");
     const run = await client.start();
 
     const inserted = await client.insert(testJob, {});
-    await waitFor(() => executor.diagnostics().activeThreads === 1);
+    await started;
     await client.jobs.cancel(inserted.job.id);
 
     await expect(
@@ -118,13 +127,13 @@ describe("WorkerThreads with River clients", () => {
 
   it("persists an ignored cancellation only after terminating its thread", async () => {
     await using executor = new WorkerThreads({ maxThreads: 1 });
-    const { client, driver } = await setup(executor, "spin", {
+    const { client, driver, started } = await setup(executor, "spin", {
       milliseconds: 10,
     });
     const run = await client.start();
 
     const inserted = await client.insert(testJob, {});
-    await waitFor(() => executor.diagnostics().activeThreads === 1);
+    await started;
     await client.jobs.cancel(inserted.job.id);
 
     await expect(
@@ -141,13 +150,13 @@ describe("WorkerThreads with River clients", () => {
 
   it("fails an attempt whose thread ignored a stop's abort, after the stuck threshold", async () => {
     await using executor = new WorkerThreads({ maxThreads: 1 });
-    const { client, driver } = await setup(executor, "spin", {
+    const { client, driver, started } = await setup(executor, "spin", {
       milliseconds: 200,
     });
     const run = await client.start();
 
     const spinning = await client.insert(testJob, {});
-    await waitFor(() => executor.diagnostics().activeThreads === 1);
+    await started;
     // The client works two jobs, so this one waits for the busy thread.
     const waiting = await client.insert(testJob, {});
     await waitFor(() => executor.diagnostics().pendingTasks === 1);
@@ -176,11 +185,11 @@ describe("WorkerThreads with River clients", () => {
 
   it("interrupts a handler that stops because of a stop's abort without using its attempt", async () => {
     await using executor = new WorkerThreads({ maxThreads: 1 });
-    const { client, driver } = await setup(executor, "cooperate");
+    const { client, driver, started } = await setup(executor, "cooperate");
     const run = await client.start();
 
     const inserted = await client.insert(testJob, {});
-    await waitFor(() => executor.diagnostics().activeThreads === 1);
+    await started;
     await run.stop({ mode: "cancel" });
 
     await expect(client.jobs.get(inserted.job.id)).resolves.toMatchObject({
diff --git a/js/worker-threads/src/index.test.ts b/js/worker-threads/src/index.test.ts
index 76f70317b..bf12cb0ca 100644
--- a/js/worker-threads/src/index.test.ts
+++ b/js/worker-threads/src/index.test.ts
@@ -67,6 +67,27 @@ describe("WorkerThreads", () => {
     expect(executor.diagnostics()).toMatchObject({ totalThreads: 0 });
   });
 
+  it("does not invoke a handler aborted while its module loads", async () => {
+    await using executor = new WorkerThreads({ maxThreads: 1 });
+    const loading = signals();
+    const target = executor.handler(testJob, {
+      exportName: "complete",
+      module: new URL("./testdata/loading.js", import.meta.url),
+    });
+    const handle = executor.start(context({}, loading), target.handler);
+    const rejected = expect(handle.result).rejects.toMatchObject({
+      message: "cancelled while loading",
+    });
+
+    await loading.next();
+    await expect(
+      handle.abort(new Error("cancelled while loading"), {
+        gracePeriod: gracePeriod(1_000),
+      })
+    ).resolves.toEqual({ terminated: false });
+    await rejected;
+  });
+
   it("reports an attempt as started only once a thread takes it", async () => {
     const executor = new WorkerThreads({ maxThreads: 1 });
     const started = signals();
@@ -867,10 +888,10 @@ describe("WorkerThreads", () => {
     });
   });
 
-  it("revives execution timestamps with the worker realm's native Temporal", async () => {
+  it("revives execution timestamps with the worker realm's Temporal", async () => {
     const executor = new WorkerThreads({ maxThreads: 1 });
     const target = executor.handler(testJob, {
-      exportName: "confirmNativeTemporal",
+      exportName: "confirmTemporal",
       module: handlers,
     });
 
diff --git a/js/worker-threads/src/testdata/handlers.ts b/js/worker-threads/src/testdata/handlers.ts
index c69f81e2d..360339881 100644
--- a/js/worker-threads/src/testdata/handlers.ts
+++ b/js/worker-threads/src/testdata/handlers.ts
@@ -27,9 +27,9 @@ export const allocateForever: TestHandler = ({ logger }) => {
 export const complete: TestHandler = ({ job }) =>
   completeOutcome({ output: { value: job.args.value ?? null } });
 
-export const confirmNativeTemporal: TestHandler = ({ execution }) => {
+export const confirmTemporal: TestHandler = ({ execution }) => {
   if (!(execution.startedAt instanceof Temporal.Instant)) {
-    throw new TypeError("startedAt is not a native Temporal.Instant");
+    throw new TypeError("startedAt is not a Temporal.Instant from this realm");
   }
   return completeOutcome({
     output: { startedAt: execution.startedAt.toString() },
diff --git a/js/worker-threads/src/testdata/loading.ts b/js/worker-threads/src/testdata/loading.ts
new file mode 100644
index 000000000..cf8da4a64
--- /dev/null
+++ b/js/worker-threads/src/testdata/loading.ts
@@ -0,0 +1,17 @@
+import { parentPort } from "node:worker_threads";
+
+// The test starts this module as task 1 in a fresh pool. Report that its
+// import is pending and finish importing only once the abort message arrives.
+await new Promise<void>((resolve) => {
+  parentPort?.once("message", () => resolve());
+  parentPort?.postMessage({
+    level: "info",
+    message: "started",
+    taskId: 1,
+    type: "log",
+  });
+});
+
+export function complete(): never {
+  throw new Error("aborted handler was invoked");
+}
diff --git a/js/worker-threads/src/thread.ts b/js/worker-threads/src/thread.ts
index c730d6adf..a8492bb09 100644
--- a/js/worker-threads/src/thread.ts
+++ b/js/worker-threads/src/thread.ts
@@ -98,6 +98,9 @@ async function run(message: RunMessage, signal: AbortSignal): Promise<void> {
   try {
     const context = workContext(message, signal);
     const module = (await import(message.moduleUrl)) as Record<string, unknown>;
+    // Cancellation can arrive while the handler module is still loading.
+    // Do not invoke a handler after its signal has already been aborted.
+    signal.throwIfAborted();
     const handler = module[message.exportName];
     if (typeof handler !== "function") {
       throw new TypeError(