diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 547b007..e7555f2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -127,6 +127,33 @@ jobs:
           echo "wanted=${expected} actual=${actual}"
           case "${actual}" in "v${expected}"*) ;; *) echo "::error::node mismatch"; exit 1 ;; esac
 
+      # `registry-url` is what kept every release workflow off this action: measured 2026-09-05,
+      # seven of the nine `release.yml` in this ecosystem pass it, and the action did not accept
+      # it — so adopting the shared setup meant losing npm authentication. It is a passthrough to
+      # `actions/setup-node`, and a passthrough nobody exercises is a passthrough that can be
+      # silently dropped in a refactor.
+      - name: Run the action again, asking for a registry
+        uses: ./actions/setup
+        with:
+          node-version: ${{ matrix.node }}
+          working-directory: fixtures/pnpm-repo
+          # No install: the toolchain and the .npmrc are the whole subject here.
+          install: 'false'
+          registry-url: 'https://registry.npmjs.org'
+      - name: setup-node wrote an npmrc binding the token
+        shell: bash
+        # Asserting the FILE rather than `npm config get registry`, because the latter reads the
+        # effective config and would go green on a registry that came from somewhere else — the
+        # claim under test is that this action caused it.
+        run: |
+          set -euo pipefail
+          : "${NPM_CONFIG_USERCONFIG:?setup-node did not point NPM_CONFIG_USERCONFIG anywhere}"
+          echo "userconfig: ${NPM_CONFIG_USERCONFIG}"
+          test -f "${NPM_CONFIG_USERCONFIG}"
+          grep -q 'registry.npmjs.org' "${NPM_CONFIG_USERCONFIG}"
+          grep -q '_authToken' "${NPM_CONFIG_USERCONFIG}"
+          echo "npmrc names the registry and binds _authToken"
+
   npm-oidc-action:
     name: npm-oidc action
     runs-on: ubuntu-latest
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 35e91c3..57dafad 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,22 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- **`actions/setup` accepts `registry-url`, which is what kept every release workflow off it
+  (#54).** Measured 2026-09-05 across the ten consumers: **22 workflows set up Node and pnpm by
+  hand, and exactly one file used this action.** The largest group of duplicates is the nine
+  `release.yml`, and **seven of them pass `registry-url`** — so adopting the shared setup meant
+  losing npm authentication. One missing passthrough was holding the whole adoption.
+
+  Everything else was already equivalent, including the part most likely to be lost in a rewrite:
+  the action's `cache-dependency-path` already lists `package.json` beside `pnpm-lock.yaml`, which
+  is the fix for a pnpm major bump restoring a store the new pnpm reads as inconsistent
+  (`ERR_PNPM_MISSING_PACKAGE_INDEX_FILE`).
+
+  Exercised rather than asserted: the action's own CI job now runs it with a registry and checks
+  that `setup-node` wrote an `.npmrc` naming the registry and binding `_authToken`. The assertion
+  reads the FILE rather than `npm config get registry`, because the latter would go green on a
+  registry that came from somewhere else.
+
 - **`promotion-gate.yml` is now a reusable workflow, so the gate that protects `develop` has one
   home instead of ten (#51).** Measured 2026-09-05 across the ten consumers of this repository:
   nine held **byte-identical** copies of a 74-line gate (identical after stripping comments and
diff --git a/actions/setup/action.yml b/actions/setup/action.yml
index 777451e..1837b8c 100644
--- a/actions/setup/action.yml
+++ b/actions/setup/action.yml
@@ -35,6 +35,19 @@ inputs:
       has to say so here — otherwise the install runs against nothing and reports success.
     required: false
     default: '.'
+  registry-url:
+    description: >-
+      Passed straight to `actions/setup-node`, which writes an `.npmrc` binding
+      `_authToken` to `NODE_AUTH_TOKEN`. A publishing job needs it; nothing else does, so it is
+      empty by default and `setup-node` then writes no `.npmrc` at all.
+
+      This input exists because its absence was what kept every release workflow off this action.
+      Measured 2026-09-05 across the ten consumers: 22 workflows set up Node and pnpm by hand and
+      exactly one file used this action. Of the nine `release.yml`, SEVEN pass `registry-url` —
+      so for the largest group of duplicates, adopting the shared setup meant losing npm
+      authentication. One missing passthrough was holding the whole adoption.
+    required: false
+    default: ''
 
 outputs:
   package-manager-version:
@@ -62,6 +75,8 @@ runs:
       with:
         node-version: ${{ inputs.node-version }}
         node-version-file: ${{ inputs.node-version == '' && format('{0}/.nvmrc', inputs.working-directory) || '' }}
+        # Empty writes no `.npmrc`, which is what every non-publishing job wants.
+        registry-url: ${{ inputs.registry-url }}
         cache: pnpm
         # The cache key must change when the package manager does. setup-node keys the pnpm store on
         # the lockfile alone, so a pnpm 9 -> 10 bump leaves the key identical and the job restores a