diff --git a/docs/rules/catalogue.adoc b/docs/rules/catalogue.adoc
index de57dbaa..bdef9962 100644
--- a/docs/rules/catalogue.adoc
+++ b/docs/rules/catalogue.adoc
@@ -16,7 +16,7 @@ a blank ID column means the module emits atom-keyed findings rather than prefixe
 [cols="34,33,33",options="header"]
 |===
 |Module |Rule IDs |Purpose
-|`+actions_lock+` |— |Strict local validation for machine-generated `gh actions-lock` v0.0.2 files.
+|`+actions_lock+` |— |Strict local validation for machine-generated `gh actions-lock` v0.0.2 and v0.0.3 files.
 |`+admin_merge_eligibility+` |DBA002 |Recognises PR shapes that are safe to admin-merge in bulk when the
 |`+baseline_health+` |BH001 BH002 BH003 BH004 BH005 BH006 BH007 BH008 |Detects degraded `main`-branch baseline conditions that allow silent rot.
 |`+branch_protection+` |BP001 BP002 BP003 BP004 BP005 BP006 BP007 BP008 BP009 |Branch-protection hygiene rules drawn from the CIS GitHub Benchmark,
diff --git a/lib/rules/actions_lock.ex b/lib/rules/actions_lock.ex
index 85b3b8b1..3a292443 100644
--- a/lib/rules/actions_lock.ex
+++ b/lib/rules/actions_lock.ex
@@ -378,6 +378,8 @@ defmodule Hypatia.Rules.ActionsLock do
   defp finalize_dependency(state) do
     {key, dependency, header_line} = state.current_dependency
     normalized = normalise_ref(key)
+    # nil is the home host; v0.0.3 records owner and repo IDs per host.
+    hostname = Map.get(dependency, :hostname)
 
     with {:ok, ref} <- fetch_dependency_field(dependency, :ref, key, header_line),
          {:ok, commit} <- fetch_dependency_field(dependency, :commit, key, header_line),
diff --git a/test/rules/actions_lock_test.exs b/test/rules/actions_lock_test.exs
index b76ce699..b1c64e99 100644
--- a/test/rules/actions_lock_test.exs
+++ b/test/rules/actions_lock_test.exs
@@ -285,8 +285,7 @@ defmodule Hypatia.Rules.ActionsLockTest do
   test "rejects symbolic-ref and SHA-key contradictions" do
     symbolic = String.replace(@valid_lock, "ref: 'v7.0.1'", "ref: 'v6.0.0'")
 
-    assert {:error, {:line, _, {:symbolic_key_ref_mismatch, _, _}}} =
-             ActionsLock.parse(symbolic)
+    assert {:error, {:line, _, {:symbolic_key_ref_mismatch, _, _}}} = ActionsLock.parse(symbolic)
 
     sha_key = """
     version: 'v0.0.2'
@@ -449,12 +448,92 @@ defmodule Hypatia.Rules.ActionsLockTest do
         "    'actions/checkout@refs:heads/main':\n"
       )
 
-    assert {:error, {:line, _, {:malformed_dependency_key, _}}} =
-             ActionsLock.parse(subpath_key)
+    assert {:error, {:line, _, {:malformed_dependency_key, _}}} = ActionsLock.parse(subpath_key)
 
     assert {:error, {:line, _, {:malformed_dependency_key, _}}} = ActionsLock.parse(colon_key)
   end
 
+  test "accepts v0.0.3 locks and validates the optional hostname" do
+    v3 = String.replace(@valid_lock, "v0.0.2", "v0.0.3")
+    assert {:ok, %ActionsLock{version: "v0.0.3"}} = ActionsLock.parse(v3)
+
+    with_host = fn host ->
+      String.replace(
+        v3,
+        "        repo_id: 197814629\n",
+        "        repo_id: 197814629\n        hostname: '#{host}'\n"
+      )
+    end
+
+    assert {:ok, _} = ActionsLock.parse(with_host.("github.com"))
+    assert {:ok, _} = ActionsLock.parse(with_host.("acme.ghe.com"))
+
+    long_label = String.duplicate("a", 64) <> ".ghe.com"
+    assert {:ok, _} = ActionsLock.parse(with_host.(String.duplicate("a", 63) <> ".ghe.com"))
+
+    for bad <- [
+          "GitHub.com",
+          "example.com",
+          "acme.ghe.com.evil",
+          "-x.ghe.com",
+          "foo.bar.ghe.com",
+          long_label
+        ] do
+      assert {:error, {:line, _, {:malformed_dependency_hostname, ^bad}}} =
+               ActionsLock.parse(with_host.(bad))
+    end
+
+    dup =
+      String.replace(
+        with_host.("github.com"),
+        "hostname: 'github.com'\n",
+        "hostname: 'github.com'\n        hostname: 'github.com'\n"
+      )
+
+    assert {:error, {:line, _, {:duplicate_dependency_field, _, :hostname}}} =
+             ActionsLock.parse(dup)
+
+    v2_with_host =
+      String.replace(
+        @valid_lock,
+        "        repo_id: 197814629\n",
+        "        repo_id: 197814629\n        hostname: 'github.com'\n"
+      )
+
+    assert {:error, {:line, _, :malformed_dependency_hostname}} = ActionsLock.parse(v2_with_host)
+  end
+
+  test "scopes owner and repository identities to their v0.0.3 host" do
+    mixed = """
+    version: 'v0.0.3'
+    workflows:
+        '.github/workflows/ci.yml':
+            - 'acme/foo@v1'
+            - 'acme/bar@v1'
+    dependencies:
+        'acme/bar@v1':
+            hostname: 'github.com'
+            ref: 'v1'
+            commit: 'sha1-3d3c42e5aac5ba805825da76410c181273ba90b1'
+            owner_id: 2
+            repo_id: 20
+        'acme/foo@v1':
+            ref: 'v1'
+            commit: 'sha1-3d3c42e5aac5ba805825da76410c181273ba90b1'
+            owner_id: 1
+            repo_id: 20
+    """
+
+    assert {:ok, lock} = ActionsLock.parse(mixed)
+    assert lock.dependencies["acme/bar@v1"].hostname == "github.com"
+    assert lock.dependencies["acme/foo@v1"].hostname == nil
+
+    same_host = String.replace(mixed, "        hostname: 'github.com'\n", "")
+
+    assert {:error, {:line, _, {:owner_identity_mismatch, "acme", 2, 1}}} =
+             ActionsLock.parse(same_host)
+  end
+
   test "parses the repository's authoritative generated lockfile" do
     content = File.read!(".github/workflows/actions.lock")
     assert {:ok, parsed} = ActionsLock.parse(content)