diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4cec919..970bee0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,6 +5,10 @@ on:
     branches: [master]
   pull_request:
   workflow_dispatch:
+  # Lets the release workflow run this exact gate (lint + test matrix +
+  # package) before publishing, instead of duplicating it. workflow_call adds
+  # no automatic runs of its own.
+  workflow_call:
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
@@ -27,13 +31,13 @@ jobs:
     name: Lint and type-check
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
         with:
           # Don't leave GITHUB_TOKEN in .git/config for later steps to reach.
           persist-credentials: false
 
       - name: Install uv
-        uses: astral-sh/setup-uv@v5
+        uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5
         with:
           enable-cache: true
 
@@ -69,13 +73,13 @@ jobs:
       matrix:
         python-version: ["3.11", "3.12", "3.13"]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
         with:
           # Don't leave GITHUB_TOKEN in .git/config for later steps to reach.
           persist-credentials: false
 
       - name: Install uv
-        uses: astral-sh/setup-uv@v5
+        uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5
         with:
           enable-cache: true
           python-version: ${{ matrix.python-version }}
@@ -93,13 +97,13 @@ jobs:
     name: Build and verify distributions
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
         with:
           # Don't leave GITHUB_TOKEN in .git/config for later steps to reach.
           persist-credentials: false
 
       - name: Install uv
-        uses: astral-sh/setup-uv@v5
+        uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5
         with:
           enable-cache: true
 
@@ -116,7 +120,7 @@ jobs:
       - name: Verify distribution contents
         run: uv run --no-project python scripts/check_dist.py
 
-      - uses: actions/upload-artifact@v4
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
         with:
           name: distributions
           path: dist/
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
new file mode 100644
index 0000000..205edf8
--- /dev/null
+++ b/.github/workflows/release.yml
@@ -0,0 +1,114 @@
+name: Release
+
+# Publishes to PyPI via Trusted Publishing (OIDC)
+# Two paths:
+#
+#   * Push a tag `vX.Y.Z`           -> validate, build, verify, publish to PyPI.
+#   * Run manually (workflow_dispatch) -> validate, build, verify, publish to
+#     TestPyPI, for a dry run of the whole pipeline against a throwaway index.
+#
+# A pending publisher must be registered on the target index (PyPI and/or
+# TestPyPI) pointing at this repo + release.yml + the matching environment.
+# That is a one-time web step and cannot be done here.
+#
+# Third-party actions are pinned to full commit SHAs (version in a comment).
+# This job graph carries `id-token: write`, so a moving tag on a compromised
+# action could exfiltrate the OIDC token or tamper with the artifact.
+
+on:
+  push:
+    tags:
+      - "v*"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  # Run the full PR gate -- lint, type-check, the 3-version test matrix, and
+  # the packaging check -- before anything is published. Publishing is
+  # irreversible per version, and a tag can point at any commit, including one
+  # that never went through CI. Reused from ci.yml rather than duplicated, so
+  # the release gate cannot drift from the everyday one.
+  checks:
+    uses: ./.github/workflows/ci.yml
+    permissions:
+      contents: read
+
+  build:
+    name: Build and verify distributions
+    needs: checks
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
+        with:
+          persist-credentials: false
+
+      - name: Install uv
+        # No build cache: this build becomes an unremovable public artifact, so
+        # it is produced from a clean environment rather than a restored cache.
+        uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5
+
+      # Guard against the one mistake tags make: a vX.Y.Z tag whose number does
+      # not match pyproject. PyPI would publish whatever pyproject says, under a
+      # version the tag does not describe -- and it could never be corrected.
+      - name: Tag matches package version
+        if: startsWith(github.ref, 'refs/tags/v')
+        run: |
+          tag="${GITHUB_REF_NAME#v}"
+          pkg="$(python -c "import tomllib; print(tomllib.load(open('pyproject.toml','rb'))['project']['version'])")"
+          echo "tag=$tag  pyproject=$pkg"
+          if [ "$tag" != "$pkg" ]; then
+            echo "::error::tag v$tag does not match pyproject version $pkg"
+            exit 1
+          fi
+
+      - name: Build sdist and wheel
+        run: uv build
+
+      # Same guard CI runs on every PR: required data ships, no test fixtures
+      # or signing material leak. Doubly worth it here -- this build is the one
+      # that becomes an unremovable public artifact.
+      - name: Verify distribution contents
+        run: uv run --no-project python scripts/check_dist.py
+
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
+        with:
+          name: release-dist
+          path: dist/
+
+  publish-testpypi:
+    name: Publish to TestPyPI (dry run)
+    if: github.event_name == 'workflow_dispatch'
+    needs: build
+    runs-on: ubuntu-latest
+    environment: testpypi
+    permissions:
+      id-token: write # OIDC token for Trusted Publishing; no stored secret.
+    steps:
+      - uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
+        with:
+          name: release-dist
+          path: dist/
+
+      - name: Publish
+        uses: pypa/gh-action-pypi-publish@ba38be9e461d3875417946c167d0b5f3d385a247 # release/v1
+        with:
+          repository-url: https://test.pypi.org/legacy/
+
+  publish-pypi:
+    name: Publish to PyPI
+    if: startsWith(github.ref, 'refs/tags/v')
+    needs: build
+    runs-on: ubuntu-latest
+    environment: pypi
+    permissions:
+      id-token: write
+    steps:
+      - uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
+        with:
+          name: release-dist
+          path: dist/
+
+      - name: Publish
+        uses: pypa/gh-action-pypi-publish@ba38be9e461d3875417946c167d0b5f3d385a247 # release/v1