diff --git a/.github/actions/npm-publish-hardened/README.md b/.github/actions/npm-publish-hardened/README.md
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+# npm-publish-hardened
+
+Composite action that publishes a single npm package using **OIDC
+trusted publishing** with **SLSA v1 provenance**. Refuses to fall
+back to `NPM_TOKEN` auth and is idempotent over the package version.
+
+## What it does
+
+1. Hard-fails if `NPM_TOKEN` or `NODE_AUTH_TOKEN` is in the
+   environment. Trusted publishing is via OIDC token exchange; if a
+   legacy token is present the publish would silently use it instead
+   and defeat the purpose.
+2. Verifies the npm CLI is v11.5.1+ (the cutoff for trusted
+   publishing support).
+3. Skips publish if the exact `name@version` from `package.json` is
+   already on the registry (re-runs of the same release are no-ops).
+4. Runs `npm publish --provenance --access public --tag <tag>`. npm
+   detects the GitHub Actions OIDC env vars
+   (`ACTIONS_ID_TOKEN_REQUEST_URL` and `_TOKEN`) and exchanges them
+   for a one-shot registry token automatically.
+5. Retries with exponential-ish backoff if publish reports failure
+   but the version becomes visible (registry eventual consistency).
+
+## Caller requirements
+
+```yaml
+permissions:
+  id-token: write     # required for the OIDC exchange
+  contents: read      # if the caller checks out the repo
+  attestations: write # if the caller wants provenance attestations
+                      # uploaded to GitHub as well
+```
+
+The calling job must have set up Node + npm 11.5.1+ before calling
+the action. The standard pattern:
+
+```yaml
+- uses: actions/setup-node@<sha>  # v6
+  with:
+    node-version: "22"
+    registry-url: https://registry.npmjs.org
+- run: npm install --global npm@11
+```
+
+## One-time per-package configuration on npmjs.com
+
+Trusted publishing also needs the npm side to know which repository
+and workflow are allowed to publish:
+
+1. Sign in to npmjs.com as a maintainer of the package.
+2. Package settings → **Publishing access** → **Add trusted
+   publisher**.
+3. Select GitHub Actions. Fill in:
+   - Organization: `stella`
+   - Repository: e.g. `anonymize`
+   - Workflow filename: `release.yml`
+   - Environment: leave empty unless the caller uses a deployment
+     environment (recommended for added gating)
+4. Save.
+
+Until that record exists for a package, the action will fail at
+publish time with a 401.
+
+## Usage
+
+```yaml
+- uses: stella/.github/.github/actions/npm-publish-hardened@<sha>
+  with:
+    package-dir: packages/anonymize
+    # tag: latest    # default
+```
+
+## Inputs
+
+| Name          | Required | Default  | Description                                                          |
+| ------------- | -------- | -------- | -------------------------------------------------------------------- |
+| `package-dir` | yes      | —        | Working directory containing the package's `package.json`            |
+| `tag`         | no       | `latest` | npm dist-tag for the publish                                         |
+
+## Why a composite action and not a reusable workflow
+
+The publish step is what's actually shared across publishing repos.
+Build/test scaffolding diverges (napi-rs cross-compilation,
+TypeScript bundling, etc.) and a full reusable workflow would need
+30+ inputs to handle every shape. Composite keeps the scope tight to
+the part that's identical across all callers.
diff --git a/.github/actions/npm-publish-hardened/action.yml b/.github/actions/npm-publish-hardened/action.yml
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+name: Hardened npm publish (OIDC + idempotent)
+description: >
+  Publish a single npm package via OIDC trusted publishing with SLSA
+  provenance attestation. Idempotent — skips if the exact version is
+  already on the registry. Refuses to fall back to NPM_TOKEN auth.
+
+  Caller workflow must declare `permissions: id-token: write` on the
+  calling job, and have set up npm CLI v11.5.1+ (which detects the
+  GitHub Actions OIDC env vars and performs the token exchange
+  automatically).
+
+  One-time per-package configuration is required on the npm side:
+  npmjs.com → package settings → Publishing → add a trusted publisher
+  pointing at this GitHub repository and workflow path. Without this,
+  the action will fail at publish time with a 401.
+
+inputs:
+  package-dir:
+    description: Working directory containing the package's package.json
+    required: true
+  tag:
+    description: npm dist-tag for the publish (e.g. latest, next, rc)
+    required: false
+    default: latest
+
+runs:
+  using: composite
+  steps:
+    - name: Publish
+      shell: bash
+      working-directory: ${{ inputs.package-dir }}
+      env:
+        DIST_TAG: ${{ inputs.tag }}
+      run: ${{ github.action_path }}/publish.sh
diff --git a/.github/actions/npm-publish-hardened/publish.sh b/.github/actions/npm-publish-hardened/publish.sh
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+#!/usr/bin/env bash
+# Hardened npm publish via OIDC trusted publishing.
+# See action.yml for the contract.
+
+set -euo pipefail
+
+# Defence in depth: trusted publishing performs auth via the OIDC token
+# exchange. If a legacy token is in env, the publish below would silently
+# fall back to bearer auth and the whole point of this action is lost.
+if [[ -n "${NPM_TOKEN:-}" || -n "${NODE_AUTH_TOKEN:-}" ]]; then
+  printf '::error::NPM_TOKEN/NODE_AUTH_TOKEN must not be set when using %s\n' \
+    "the hardened publish action — trusted publishing only." >&2
+  exit 2
+fi
+
+# npm 11.5.1 introduced trusted publishing support. Older clients silently
+# skip the OIDC exchange and try anonymous publish → 401.
+NPM_VERSION=$(npm --version)
+IFS='.' read -r NPM_MAJOR NPM_MINOR NPM_PATCH <<<"${NPM_VERSION}"
+# Strip any pre-release suffix from the patch component (e.g. "1-beta.0").
+NPM_PATCH=${NPM_PATCH%%-*}
+NPM_MAJOR=${NPM_MAJOR:-0}
+NPM_MINOR=${NPM_MINOR:-0}
+NPM_PATCH=${NPM_PATCH:-0}
+if (( NPM_MAJOR < 11 )) \
+   || (( NPM_MAJOR == 11 && NPM_MINOR < 5 )) \
+   || (( NPM_MAJOR == 11 && NPM_MINOR == 5 && NPM_PATCH < 1 )); then
+  printf '::error::npm %s is too old; trusted publishing requires 11.5.1+.\n' \
+    "${NPM_VERSION}" >&2
+  exit 2
+fi
+
+PACKAGE_NAME=$(node -p "require('./package.json').name")
+PACKAGE_VERSION=$(node -p "require('./package.json').version")
+
+# Idempotency: skip if exact version is already published. `npm view`
+# exits non-zero when the version doesn't exist, so the && guard handles
+# both "not published" and any view-time errors uniformly.
+already_published() {
+  local seen
+  seen=$(npm view "${PACKAGE_NAME}@${PACKAGE_VERSION}" version 2>/dev/null) || return 1
+  [[ "${seen}" == "${PACKAGE_VERSION}" ]]
+}
+
+if already_published; then
+  printf '::notice::%s@%s already published; skipping.\n' \
+    "${PACKAGE_NAME}" "${PACKAGE_VERSION}"
+  exit 0
+fi
+
+# Publish. npm 11.5+ auto-detects ACTIONS_ID_TOKEN_REQUEST_URL and
+# ACTIONS_ID_TOKEN_REQUEST_TOKEN (set by GitHub Actions when the calling
+# job has `id-token: write`) and exchanges the OIDC token for a one-shot
+# registry token. --provenance generates the SLSA v1 attestation.
+PUBLISH_LOG="${RUNNER_TEMP:-/tmp}/npm-publish-${PACKAGE_NAME//\//-}.log"
+if npm publish --provenance --access public --tag "${DIST_TAG}" 2>"${PUBLISH_LOG}"; then
+  exit 0
+fi
+
+cat "${PUBLISH_LOG}" >&2
+
+# Eventual-consistency retry: npm publish occasionally reports failure
+# while the artifact has actually been accepted, but registry visibility
+# lags behind by a few seconds. Poll for the new version before giving up.
+for attempt in 1 2 3 4 5; do
+  sleep "${attempt}"
+  if already_published; then
+    printf '::notice::%s@%s became visible after publish failure; treating as success.\n' \
+      "${PACKAGE_NAME}" "${PACKAGE_VERSION}"
+    exit 0
+  fi
+done
+
+exit 1