Fetch full history in CI and skip frozen-commit tests without it

.github/workflows/tests.yml

@@ -10,6 +10,10 @@ jobs:
         python-version: ["3.11", "3.12"]
     steps:
       - uses: actions/checkout@v4
+        with:
+          # tests/test_osf_deposit.py reads the frozen prereg-v1 commit
+          # (0a5e794) from git; the default depth-1 checkout lacks it.
+          fetch-depth: 0
       - uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}

tests/test_osf_deposit.py

@@ -1,5 +1,7 @@
 """Frozen prereg hashes must match git at 0a5e794. No network."""
 
+import subprocess
+
 from tpl.io.osf_deposit import (
     FROZEN_COMMIT,
     FROZEN_SHA256,
@@ -10,6 +12,38 @@
 import pytest
 
 
+def _frozen_commit_available():
+    """True if FROZEN_COMMIT is in the git repository of the current directory.
+
+    osf_deposit reads the frozen files with `git show` from the current
+    directory, so the check runs there too. It is false in a shallow clone
+    (CI checkout at depth 1), in a release zip/tarball (no .git), or when git
+    is not installed.
+    """
+    try:
+        subprocess.run(
+            ["git", "cat-file", "-e", f"{FROZEN_COMMIT}^{{commit}}"],
+            check=True,
+            capture_output=True,
+        )
+    except (OSError, subprocess.CalledProcessError):
+        return False
+    return True
+
+
+# Skip rather than fail: the hashes cannot be checked without the commit, and a
+# missing commit says nothing about whether they match. Run from a full clone
+# (`git fetch --unshallow` in a shallow one) to exercise these tests.
+requires_frozen_commit = pytest.mark.skipif(
+    not _frozen_commit_available(),
+    reason=(
+        f"frozen commit {FROZEN_COMMIT[:7]} (prereg-v1) is not in this checkout "
+        "(shallow clone or release archive); clone the full history to run"
+    ),
+)
+
+
+@requires_frozen_commit
 def test_snapshot_matches_pinned_hashes():
     snap = snapshot()
     assert set(snap) == set(FROZEN_SHA256)
@@ -18,6 +52,7 @@ def test_snapshot_matches_pinned_hashes():
         assert rec["nbytes"] == len(rec["bytes"])
 
 
+@requires_frozen_commit
 def test_manifest_points_at_the_freeze_not_head():
     man = manifest()
     assert man["commit"] == FROZEN_COMMIT
@@ -30,6 +65,7 @@ def test_upload_refuses_an_empty_token():
         upload("")
 
 
+@requires_frozen_commit
 def test_write_bundle_matches_git(tmp_path):
     from tpl.io.osf_deposit import write_bundle