diff --git a/test/fixtures/actions_lock/closure/closed-case-variant.lock b/test/fixtures/actions_lock/closure/closed-case-variant.lock
new file mode 100644
index 00000000..6eee99b4
--- /dev/null
+++ b/test/fixtures/actions_lock/closure/closed-case-variant.lock
@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: MPL-2.0
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+# Closure corpus fixture: closed: owner/repo spelled in another case than its record (GitHub canonicalises owner/repo). Contract: expected.tsv in this directory.
+version: 'v0.0.3'
+workflows:
+    '.github/workflows/rust.yml':
+        - 'Example/Rust-Cache@5555555555555555555555555555555555555555'
+dependencies:
+    'example/rust-cache@5555555555555555555555555555555555555555':
+        ref: 'v2.9.2'
+        commit: 'sha1-5555555555555555555555555555555555555555'
+        owner_id: 101
+        repo_id: 205
diff --git a/test/fixtures/actions_lock/closure/closed-v0.0.2.lock b/test/fixtures/actions_lock/closure/closed-v0.0.2.lock
new file mode 100644
index 00000000..5a2d04c0
--- /dev/null
+++ b/test/fixtures/actions_lock/closure/closed-v0.0.2.lock
@@ -0,0 +1,21 @@
+# SPDX-License-Identifier: MPL-2.0
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+# Closure corpus fixture: closed, format v0.0.2. Contract: expected.tsv in this directory.
+version: 'v0.0.2'
+workflows:
+    '.github/workflows/ci.yml':
+        - 'example/build@1111111111111111111111111111111111111111'
+    '.github/workflows/empty.yml': []
+dependencies:
+    'example/build@1111111111111111111111111111111111111111':
+        ref: 'v1.0.0'
+        commit: 'sha1-1111111111111111111111111111111111111111'
+        owner_id: 101
+        repo_id: 201
+        uses:
+            - 'example/setup@2222222222222222222222222222222222222222'
+    'example/setup@2222222222222222222222222222222222222222':
+        ref: 'v2.0.0'
+        commit: 'sha1-2222222222222222222222222222222222222222'
+        owner_id: 101
+        repo_id: 202
diff --git a/test/fixtures/actions_lock/closure/closed-v0.0.3.lock b/test/fixtures/actions_lock/closure/closed-v0.0.3.lock
new file mode 100644
index 00000000..381077f1
--- /dev/null
+++ b/test/fixtures/actions_lock/closure/closed-v0.0.3.lock
@@ -0,0 +1,21 @@
+# SPDX-License-Identifier: MPL-2.0
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+# Closure corpus fixture: closed, format v0.0.3 with the optional hostname field. Contract: expected.tsv in this directory.
+version: 'v0.0.3'
+workflows:
+    '.github/workflows/ci.yml':
+        - 'example/build@1111111111111111111111111111111111111111'
+dependencies:
+    'example/build@1111111111111111111111111111111111111111':
+        ref: 'v1.0.0'
+        commit: 'sha1-1111111111111111111111111111111111111111'
+        owner_id: 101
+        repo_id: 201
+        hostname: 'github.com'
+        uses:
+            - 'example/setup@2222222222222222222222222222222222222222'
+    'example/setup@2222222222222222222222222222222222222222':
+        ref: 'v2.0.0'
+        commit: 'sha1-2222222222222222222222222222222222222222'
+        owner_id: 101
+        repo_id: 202
diff --git a/test/fixtures/actions_lock/closure/dangling-nested.lock b/test/fixtures/actions_lock/closure/dangling-nested.lock
new file mode 100644
index 00000000..1b4fb80d
--- /dev/null
+++ b/test/fixtures/actions_lock/closure/dangling-nested.lock
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: MPL-2.0
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+# Closure corpus fixture: dangling: a record's nested uses: names a ref with no record (the standards#963 shape). Contract: expected.tsv in this directory.
+version: 'v0.0.2'
+workflows:
+    '.github/workflows/push.yml':
+        - 'example/push-signed@3333333333333333333333333333333333333333'
+dependencies:
+    'example/push-signed@3333333333333333333333333333333333333333':
+        ref: 'v1.3'
+        commit: 'sha1-3333333333333333333333333333333333333333'
+        owner_id: 101
+        repo_id: 203
+        uses:
+            - 'example/setup-python@v2'
diff --git a/test/fixtures/actions_lock/closure/dangling-workflow-ref.lock b/test/fixtures/actions_lock/closure/dangling-workflow-ref.lock
new file mode 100644
index 00000000..3bae2099
--- /dev/null
+++ b/test/fixtures/actions_lock/closure/dangling-workflow-ref.lock
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: MPL-2.0
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+# Closure corpus fixture: dangling: a ref under workflows: with no record. Contract: expected.tsv in this directory.
+version: 'v0.0.3'
+workflows:
+    '.github/workflows/release.yml':
+        - 'example/build@1111111111111111111111111111111111111111'
+        - 'example/generator@4444444444444444444444444444444444444444'
+dependencies:
+    'example/build@1111111111111111111111111111111111111111':
+        ref: 'v1.0.0'
+        commit: 'sha1-1111111111111111111111111111111111111111'
+        owner_id: 101
+        repo_id: 201
diff --git a/test/fixtures/actions_lock/closure/expected.tsv b/test/fixtures/actions_lock/closure/expected.tsv
new file mode 100644
index 00000000..9e07a443
--- /dev/null
+++ b/test/fixtures/actions_lock/closure/expected.tsv
@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: MPL-2.0
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+#
+# Closure corpus for actions.lock (standards#963, criterion 5). Each lock is
+# CLOSED when every ref under workflows: and every ref in a record's nested
+# uses: has a top-level dependency record, comparing owner/repo
+# case-insensitively and the ref exactly (GitHub's lockfile parser
+# canonicalises owner/repo case; see #1294 and #1314). Otherwise it is
+# DANGLING, and the third column lists the dangling refs as the lock spells
+# them, space-separated.
+#
+# Two implementations must agree with this table:
+#   * scripts/close-lock.sh --check (scripts/tests/close-lock-test.sh)
+#   * Hypatia.Rules.ActionsLock.parse/1 in hyperpolymath/hypatia, which
+#     vendors a byte-identical copy of this directory.
+# A third, GitHub's runner, is the reason the table exists.
+#
+# file	verdict	dangling
+closed-v0.0.2.lock	closed	-
+closed-v0.0.3.lock	closed	-
+closed-case-variant.lock	closed	-
+dangling-nested.lock	dangling	example/setup-python@v2
+dangling-workflow-ref.lock	dangling	example/generator@4444444444444444444444444444444444444444
diff --git a/test/rules/actions_lock_closure_corpus_test.exs b/test/rules/actions_lock_closure_corpus_test.exs
new file mode 100644
index 00000000..9f5bf0e6
--- /dev/null
+++ b/test/rules/actions_lock_closure_corpus_test.exs
@@ -0,0 +1,67 @@
+# SPDX-License-Identifier: MPL-2.0
+
+defmodule Hypatia.Rules.ActionsLockClosureCorpusTest do
+  @moduledoc """
+  Contract test for actions.lock closure, shared with hyperpolymath/standards
+  (standards#963, criterion 5).
+
+  A lock is closed when every ref under `workflows:` and in a record's nested
+  `uses:` has a top-level record of its own, with owner/repo compared
+  case-insensitively and the ref exactly. `test/fixtures/actions_lock/closure/`
+  is a byte-identical copy of standards'
+  `scripts/tests/fixtures/actions-lock-closure/`. Its `expected.tsv` gives each
+  lock's verdict and, for a dangling lock, the refs that dangle.
+
+  standards' `close-lock.sh --check` runs against the same table, so the two
+  implementations cannot drift apart without one of these suites going red.
+  Change both copies together.
+  """
+  use ExUnit.Case, async: true
+
+  alias Hypatia.Rules.ActionsLock
+
+  @dir "test/fixtures/actions_lock/closure"
+  @table Path.join(@dir, "expected.tsv")
+  @external_resource @table
+
+  @rows (for line <- String.split(File.read!(@table), "\n"),
+             line != "",
+             not String.starts_with?(line, "#") do
+           [file, verdict, dangling] = String.split(line, "\t")
+           refs = if dangling == "-", do: [], else: String.split(dangling, " ")
+           {file, verdict, refs}
+         end)
+
+  @dangling_kinds [:workflow_dependencies_missing, :transitive_dependencies_missing]
+
+  test "expected.tsv has exactly one row for each lock in the corpus" do
+    locks =
+      @dir
+      |> Path.join("*.lock")
+      |> Path.wildcard()
+      |> Enum.map(&Path.basename/1)
+      |> Enum.sort()
+
+    assert locks == @rows |> Enum.map(&elem(&1, 0)) |> Enum.sort()
+    assert length(locks) >= 5
+  end
+
+  for {file, verdict, refs} <- @rows do
+    test "#{file} is #{verdict}" do
+      result = ActionsLock.parse(File.read!(Path.join(@dir, unquote(file))))
+      assert_verdict(result, unquote(verdict), unquote(refs))
+    end
+  end
+
+  defp assert_verdict(result, "closed", []) do
+    assert {:ok, %ActionsLock{}} = result
+  end
+
+  defp assert_verdict(result, "dangling", refs) do
+    assert {:error, {kind, entries}} = result
+    assert kind in @dangling_kinds
+
+    got = entries |> Enum.map(&elem(&1, 1)) |> Enum.map(&ActionsLock.normalise_ref/1)
+    assert Enum.sort(got) == refs |> Enum.map(&ActionsLock.normalise_ref/1) |> Enum.sort()
+  end
+end