ci: publish the crate to crates.io on a v* tag

Trusted publishing is GitHub-Actions-only, so authentication goes
through a crates.io API token stored as the CARGO_REGISTRY_TOKEN
secret, scoped to the pkh crate. The job gates on the build job and
fails loudly when the tag does not match the version in Cargo.toml,
since cargo publish ships the declared version regardless of the
tag name.

.github/workflows/ci.yml

@@ -3,6 +3,7 @@ name: CI
 on:
   push:
     branches: [ "main", "ci-test" ]
+    tags: [ "v*" ]
   pull_request:
     branches: [ "main" ]
 
@@ -121,3 +122,41 @@ jobs:
           name: snap
           path: ./*.snap
           if-no-files-found: error
+
+  publish:
+    # Publishes the crate to crates.io on a v* tag. Trusted publishing
+    # (OIDC) is GitHub-Actions-only, so authentication goes through a
+    # crates.io API token stored as the CARGO_REGISTRY_TOKEN secret,
+    # scoped to the pkh crate.
+    if: startsWith(github.ref, 'refs/tags/v')
+    needs: build
+    runs-on: ubuntu-latest
+    container:
+      image: ubuntu:26.04
+      options: --privileged --cap-add SYS_ADMIN --security-opt apparmor:unconfined
+    steps:
+    - name: Set up container image
+      run: |
+        apt-get update
+        apt-get install -y nodejs sudo curl wget ca-certificates
+    - uses: actions/checkout@v6
+    - uses: dtolnay/rust-toolchain@stable
+    - name: Install build dependencies
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y pkg-config libssl-dev libgpg-error-dev libgpgme-dev
+    - name: Check the tag matches the crate version
+      # cargo publish ships whatever version Cargo.toml declares,
+      # regardless of the tag: a mismatch must fail loudly instead of
+      # publishing the wrong version under the release tag.
+      run: |
+        crate_version="$(awk -F'"' '/^version =/{print $2; exit}' Cargo.toml)"
+        tag_version="${GITHUB_REF_NAME#v}"
+        if [ "$crate_version" != "$tag_version" ]; then
+          echo "tag $GITHUB_REF_NAME does not match crate version $crate_version" >&2
+          exit 1
+        fi
+    - name: Publish
+      run: cargo publish
+      env:
+        CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }}