diff --git a/.github/workflows/release.yaml b/.github/workflows/release.yaml
index 6b77d2d..3206f65 100644
--- a/.github/workflows/release.yaml
+++ b/.github/workflows/release.yaml
@@ -91,6 +91,19 @@ jobs:
           next="${{ steps.version.outputs.next }}"
           sed -i "s/^version = \".*\"/version = \"$next\"/" pyproject.toml
           sed -i "s/^__version__ = \".*\"/__version__ = \"$next\"/" needle/__init__.py
+      # The engine wheels live on the Hub and are uploaded separately. Publishing a
+      # pin whose wheels are not there yet makes every fresh install fail at first use.
+      - if: steps.version.outputs.skip != 'true'
+        run: |
+          pip install huggingface_hub
+          python - <<'PY'
+          from needle.agent import fetch
+          missing = fetch.unpublished_engine_wheels()
+          if missing:
+              raise SystemExit("engine wheels missing from the Hub, refusing to publish:\n  "
+                               + "\n  ".join(missing))
+          print("every pinned engine is published")
+          PY
       - if: steps.version.outputs.skip != 'true'
         run: python -m build
       - if: steps.version.outputs.skip != 'true'
diff --git a/needle/agent/fetch.py b/needle/agent/fetch.py
index 52564c9..dd7055f 100644
--- a/needle/agent/fetch.py
+++ b/needle/agent/fetch.py
@@ -22,6 +22,11 @@ CHECKPOINT_PREFIX = "checkpoints"
 # Backwards-compatible aliases for callers that explicitly fetch Needle 2.
 HF_REPO = ENGINE_REPOS[2]
 
+WHEEL_TAGS = ("macosx_11_0_arm64", "macosx_11_0_x86_64",
+              "manylinux2014_aarch64", "manylinux2014_x86_64",
+              "musllinux_1_2_aarch64", "musllinux_1_2_x86_64",
+              "win_amd64", "win_arm64")
+
 PLATFORMS = ("macos-arm64", "linux-x86_64", "linux-arm64", "linux-armv7",
              "linux-riscv64", "linux-mipsel", "windows-x86_64", "windows-arm64",
              "android-arm64", "android-armv7", "android-riscv64",
@@ -95,6 +100,30 @@ def other_libc_tag():
     return None
 
 
+def engine_wheel(version, tag):
+    return "python/cactus_needle-{}-py3-none-{}.whl".format(version, tag)
+
+
+def unpublished_engine_wheels():
+    """Pinned engine wheels that are missing from the Hub, as repo-qualified paths.
+
+    ENGINE_VERSIONS and the wheels it names are published separately, so a pin
+    that lands before its upload leaves every fresh install with nothing to
+    fetch.  The release train calls this before it publishes.
+    """
+    from huggingface_hub import list_repo_files
+
+    missing = []
+    for generation in sorted(ENGINE_VERSIONS):
+        repo = ENGINE_REPOS[generation]
+        present = set(list_repo_files(repo))
+        for tag in WHEEL_TAGS:
+            wheel = engine_wheel(ENGINE_VERSIONS[generation], tag)
+            if wheel not in present:
+                missing.append(repo + "/" + wheel)
+    return missing
+
+
 def engine_repo(generation=2):
     try:
         return ENGINE_REPOS[int(generation)]
@@ -209,10 +238,9 @@ def fetch_library(version=None, dest_dir=None, tag=None, generation=2):
         raise TypeError("dest_dir is required")
     version = version or engine_version(generation)
     tag = tag or _platform_tag()
-    wheel = "cactus_needle-{}-py3-none-{}.whl".format(version, tag)
     repo = engine_repo(generation)
     _register_download(generation)
-    path = hf_hub_download(repo_id=repo, filename="python/" + wheel, repo_type="model")
+    path = hf_hub_download(repo_id=repo, filename=engine_wheel(version, tag), repo_type="model")
     lib = _lib_name_for(tag)
     stem, suffix = os.path.splitext(lib)
     member = f"{stem}{generation}{suffix}" if int(generation) >= 3 else lib
diff --git a/tests/test_fetch.py b/tests/test_fetch.py
index 159b5eb..5e59cca 100644
--- a/tests/test_fetch.py
+++ b/tests/test_fetch.py
@@ -105,6 +105,32 @@ def test_component_platform_is_downloadable():
     assert "wasm-component" in PLATFORMS
 
 
+def test_unpublished_engine_wheels_lists_every_missing_tag(monkeypatch):
+    from needle.agent import fetch
+
+    published = {
+        repo: {fetch.engine_wheel(version, tag) for tag in fetch.WHEEL_TAGS}
+        for repo, version in ((fetch.ENGINE_REPOS[2], fetch.ENGINE_VERSIONS[2]),
+                              (fetch.ENGINE_REPOS[3], fetch.ENGINE_VERSIONS[3]))
+    }
+    monkeypatch.setattr("huggingface_hub.list_repo_files",
+                        lambda repo: sorted(published[repo]) + ["needle3.cact"])
+    assert fetch.unpublished_engine_wheels() == []
+
+    repo3 = fetch.ENGINE_REPOS[3]
+    dropped = fetch.engine_wheel(fetch.ENGINE_VERSIONS[3], "win_arm64")
+    published[repo3].remove(dropped)
+    assert fetch.unpublished_engine_wheels() == [repo3 + "/" + dropped]
+
+
+def test_release_gate_runs_before_the_publish_step():
+    from pathlib import Path
+
+    workflow = Path(__file__).parents[1] / ".github/workflows/release.yaml"
+    text = workflow.read_text()
+    assert text.index("unpublished_engine_wheels") < text.index("pypa/gh-action-pypi-publish")
+
+
 def test_fetch_library_creates_destination(tmp_path, monkeypatch):
     import zipfile
     from needle.agent import fetch