diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index c5ddfcb3..7b1ccff7 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -261,7 +261,78 @@ jobs:
           path: dist
           merge-multiple: true
 
+      - name: Validate wheels
+        run: |
+          pip install twine
+          for whl in dist/*.whl; do
+            unzip -qt "$whl"
+          done
+          twine check --strict dist/*
+
+      - name: Check PyPI for existing version
+        id: pypi-check
+        run: |
+          version="${GITHUB_REF_NAME}"
+          python3 - "$version" <<'PYCHECK'
+          import hashlib, json, os, sys, urllib.request
+          from pathlib import Path
+
+          version = sys.argv[1]
+          dist = Path("dist")
+          url = f"https://pypi.org/pypi/taskito/{version}/json"
+          req = urllib.request.Request(url, headers={"User-Agent": "taskito-release/1.0"})
+
+          try:
+              resp = urllib.request.urlopen(req, timeout=30)
+              remote = {f["filename"]: f["digests"]["sha256"] for f in json.loads(resp.read())["urls"]}
+          except urllib.error.HTTPError as e:
+              if e.code == 404:
+                  remote = {}
+              else:
+                  raise
+
+          local = {}
+          for p in sorted(dist.iterdir()):
+              if p.suffix in (".whl", ".gz"):
+                  local[p.name] = hashlib.sha256(p.read_bytes()).hexdigest()
+
+          conflicts = [f for f in local if f in remote and local[f] != remote[f]]
+          if conflicts:
+              for f in conflicts:
+                  print(f"::error::Hash conflict: {f} (local {local[f][:12]}… vs remote {remote[f][:12]}…)")
+              sys.exit(1)
+
+          missing = [f for f in local if f not in remote]
+          out = os.environ["GITHUB_OUTPUT"]
+          with open(out, "a") as fh:
+              if not missing:
+                  fh.write("all_uploaded=true\n")
+                  print(f"::notice::All {len(local)} artifacts on PyPI — skipping upload")
+              else:
+                  fh.write("all_uploaded=false\n")
+                  print(f"::notice::{len(missing)}/{len(local)} artifact(s) missing on PyPI")
+          PYCHECK
+
       - name: Publish to PyPI
-        uses: pypa/gh-action-pypi-publish@release/v1
+        if: steps.pypi-check.outputs.all_uploaded != 'true'
+        uses: pypa/gh-action-pypi-publish@cef221092ed1bacb1cc03d23a2d87d1d172e277b # release/v1
         with:
           packages-dir: dist/
+          skip-existing: true
+
+      - name: Verify version on PyPI
+        run: |
+          version="${GITHUB_REF_NAME}"
+          for _attempt in 1 2 3 4 5; do
+            status=$(curl -s -o /dev/null -w '%{http_code}' --head \
+              --connect-timeout 10 --max-time 30 \
+              -H "User-Agent: taskito-release/1.0" \
+              "https://pypi.org/pypi/taskito/${version}/json")
+            if [ "$status" = "200" ]; then
+              echo "taskito==${version} live on PyPI"
+              exit 0
+            fi
+            sleep 15
+          done
+          echo "::error::taskito==${version} not found on PyPI"
+          exit 1