ci: create the GitHub release from the CHANGELOG section on tag push

.github/workflows/release.yml

@@ -0,0 +1,34 @@
+# A tag with no release reads as abandonment on the repo page: on 2026-09-01
+# four versions shipped to PyPI while "Latest" still said v0.3.1. The notes
+# already live in CHANGELOG.md, so the release is derived from it -- title
+# from the heading, body from the section -- and nothing is written twice.
+# A tag whose section is missing fails loudly instead of publishing an empty
+# release.
+name: release
+on:
+  push:
+    tags: ["v*"]
+permissions:
+  contents: write
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: release from the CHANGELOG section
+        env:
+          GH_TOKEN: ${{ github.token }}
+          TAG: ${{ github.ref_name }}
+        run: |
+          # heading: "## v0.7.0 — subtitle (2026-09-01)"; body: until the next "## "
+          awk -v tag="$TAG" '
+            /^## / { if (on) exit; on = ($2 == tag) ; if (on) { print > "/tmp/heading"; next } }
+            on { print }
+          ' CHANGELOG.md > /tmp/notes.md
+          if [ ! -s /tmp/heading ]; then
+            echo "::error::CHANGELOG.md has no '## $TAG' section; add it, then re-push the tag"
+            exit 1
+          fi
+          TITLE=$(sed -E 's/^## //; s/ \([0-9]{4}-[0-9]{2}-[0-9]{2}\)$//' /tmp/heading)
+          echo "title: $TITLE"
+          gh release create "$TAG" --verify-tag --title "$TITLE" --notes-file /tmp/notes.md