@@ -53,8 +53,8 @@
 | Field | Present when | Value |
 |---|---|---|
 | `role` | The caller has a membership in the organization on this deployment. | The stored role: `admin` or `user` in OSS; `unstract_admin`, `unstract_user`, `unstract_supervisor` or `unstract_reviewer` in cloud. |
-| `member_count` | The organization exists on this deployment. | The people the members page lists: the organization's member records on this deployment. Platform API key accounts and pending invitations are not counted. |
-| `region` | The organization exists on this deployment and the deployment sets `REGION`. | The region code (`US`, `EU`; `STAGING`, `DEV` or `INTEGRATION` outside production). The client maps it to a label. OSS and on-prem never send it: their settings don't read `REGION`, whatever the environment sets. It is the region of the deployment that answered: an organization from another region that the user once opened here has a local copy, so it shows this region and this deployment's member count. |
+| `member_count` | The organization exists on this deployment and, where the deployment sets `REGION`, its metadata doesn't name a different region. An organization created before the stamp and not back-filled carries no region, so a local copy of one from another region still sends the copy's count. | The people the members page lists: the organization's member records on this deployment. Platform API key accounts and pending invitations are not counted. |
+| `region` | The deployment sets `REGION`, and either the organization's metadata names a region or the organization exists on this deployment. | The region code (`US`, `EU`; `STAGING`, `DEV` or `INTEGRATION` outside production), from the metadata trimmed and uppercased, else this deployment's `REGION`. The client maps it to a label. OSS and on-prem never send it: their settings don't read `REGION`, whatever the environment sets. Cloud stamps `region` on an organization's metadata where it is created. An organization from another region that the user once opened here has a local copy; its row shows the home region and no `member_count`, since this deployment counts only the people who opened the copy. Organizations created before the stamp and not back-filled show the region of the deployment that answered. |
 
 If working out these three fields fails, the list is returned without them and the failure is logged.
 
 
@@ -6,12 +6,23 @@
 out of the row rather than sent as null:
 
 - ``role``: the caller has a membership row in that organization here.
-- ``member_count``: the organization exists here. Counts the people the
-  members page lists: the organization's member records here, without
-  platform API key accounts. Pending invitations have no record yet.
-- ``region``: the organization exists here and ``settings.REGION`` is set.
+- ``member_count``: the organization exists here and, where
+  ``settings.REGION`` is set, its metadata names no other region. Counts the
+  people the members page lists: the organization's member records here,
+  without platform API key accounts. Pending invitations have no record yet.
+- ``region``: only where ``settings.REGION`` is set: the region named in the
+  organization's metadata, else ``settings.REGION`` when the organization
+  exists here.
+
+Cloud stamps ``region`` on an organization's metadata where it is created.
+Opening it from another region makes a local copy there, so where the stamp
+names another region the row shows that region and leaves out this
+deployment's member count, which covers only the people who opened the copy.
+An organization without the stamp (created before it and not back-filled) is
+treated as this region's: a copy of one shows this region and the copy's count.
 """
 
+import logging
 from collections.abc import Sequence
 from typing import Any, Protocol
 
@@ -21,6 +32,8 @@
 
 from account_v2.models import Organization, User
 
+logger = logging.getLogger(__name__)
+
 
 class ListedOrganization(Protocol):
     """What the auth services return for each organization.
@@ -34,6 +47,21 @@ class ListedOrganization(Protocol):
     name: str
 
 
+def _home_region(metadata: object) -> str | None:
+    """The ``region`` in an organization's metadata (from the identity provider).
+
+    Returned trimmed and uppercased; None when there is no usable stamp.
+    """
+    stamp = metadata.get("region") if isinstance(metadata, dict) else None
+    if stamp is None:
+        return None
+    code = stamp.strip().upper() if isinstance(stamp, str) else ""
+    if not code:
+        logger.warning("Ignoring malformed region stamp %r", stamp)
+        return None
+    return code
+
+
 def with_member_details(
     organizations: Sequence[ListedOrganization], user: User
 ) -> list[dict[str, Any]]:
@@ -67,21 +95,26 @@ def with_member_details(
             user=user, organization__organization_id__in=ids
         ).values_list("organization__organization_id", "role")
     )
-    region = getattr(settings, "REGION", None)
+    region = (getattr(settings, "REGION", None) or "").strip().upper() or None
 
     rows = []
     for org in organizations:
+        metadata = getattr(org, "metadata", None)
+        home = _home_region(metadata) if region else None
         row: dict[str, Any] = {
             "id": org.id,
             "display_name": org.display_name,
             "name": org.name,
-            "metadata": getattr(org, "metadata", None),
+            "metadata": metadata,
         }
         if org.id in roles:
             row["role"] = roles[org.id]
-        if org.id in member_counts:
+        exists_here = org.id in member_counts
+        is_copy = home is not None and home != region
+        if exists_here and not is_copy:
             row["member_count"] = member_counts[org.id]
-            if region:
-                row["region"] = region
+        org_region = home or (region if exists_here else None)
+        if org_region:
+            row["region"] = org_region
         rows.append(row)
     return rows
@@ -49,13 +49,18 @@ class GetOrganizationsResponseSerializer(serializers.Serializer):
         required=False,
         help_text="The people the members page lists, without platform API key "
         "accounts. Absent if the organization has no data on this deployment, "
-        "or if the details could not be loaded.",
+        "if the deployment has regions and the organization's metadata names "
+        "another one, or if the details could not be loaded. Organizations "
+        "without a region in their metadata count as this deployment's: see "
+        "account_v2/ReadMe.md.",
     )
     region = serializers.CharField(
         required=False,
-        help_text="The deployment's region code, e.g. US or EU. Absent where "
-        "the deployment has no regions, the organization has no data here, or "
-        "the details could not be loaded.",
+        help_text="The region code, e.g. US or EU, named in the organization's "
+        "metadata, else this deployment's region if the organization exists "
+        "here. Absent where the deployment has no regions, the region is not "
+        "known here, or the details could not be loaded. See account_v2/ReadMe.md "
+        "for organizations without a region in their metadata.",
     )
 
     def to_representation(self, instance):  # type: ignore
 
@@ -164,3 +164,108 @@ def test_any_object_with_the_fields_works(self) -> None:
 
     def test_no_organizations(self) -> None:
         self.assertEqual(with_member_details([], self.caller), [])
+
+
+# Cloud stamps the region an organization was created in on its identity
+# provider metadata, which the auth service returns with each organization.
+@override_settings(REGION="US")
+class HomeRegionTests(TestCase):
+    def setUp(self) -> None:
+        self.caller = _user("caller@example.com")
+        self.org = _org("org-a", "Org A")
+        OrganizationMember.objects.create(
+            organization=self.org, user=self.caller, role="admin"
+        )
+
+    def _row(self, metadata: object, org_id: str = "org-a") -> dict:
+        org = SimpleNamespace(
+            id=org_id, display_name="Org A", name=org_id, metadata=metadata
+        )
+        return with_member_details([org], self.caller)[0]
+
+    def test_home_organisation_keeps_this_regions_details(self) -> None:
+        row = self._row({"region": "US"})
+        self.assertEqual((row["region"], row["member_count"]), ("US", 1))
+
+    def test_local_copy_shows_its_home_region(self) -> None:
+        row = self._row({"region": "EU"})
+        self.assertEqual(row["region"], "EU")
+        # This deployment's count covers only the people who opened the copy here.
+        self.assertNotIn("member_count", row)
+        self.assertEqual(row["role"], "admin")
+
+    def test_organisation_with_no_data_here_still_shows_its_region(self) -> None:
+        row = self._row({"region": "EU"}, org_id="org-x")
+        self.assertEqual(row["region"], "EU")
+        self.assertNotIn("member_count", row)
+        self.assertNotIn("role", row)
+
+    def test_unstamped_organisation_falls_back_to_this_region(self) -> None:
+        # Organizations created before the stamp, until they are back-filled.
+        row = self._row({"environment": "cloud-production"})
+        self.assertEqual((row["region"], row["member_count"]), ("US", 1))
+
+    @override_settings(REGION=None)
+    def test_deployment_without_regions_ignores_the_stamp(self) -> None:
+        # OSS and on-prem: a region key in the provider's metadata changes nothing.
+        row = self._row({"region": "EU"})
+        self.assertNotIn("region", row)
+        self.assertEqual(row["member_count"], 1)
+
+    def test_stamp_that_is_not_a_non_empty_string_is_ignored(self) -> None:
+        for stamp in ("", " ", ["EU"], 7):
+            with self.subTest(stamp=repr(stamp)):
+                with self.assertLogs("account_v2.organization_details", "WARNING"):
+                    row = self._row({"region": stamp})
+                self.assertEqual((row["region"], row["member_count"]), ("US", 1))
+
+    def test_stamp_is_compared_without_case_or_padding(self) -> None:
+        for stamp, region, count in (
+            ("us", "US", 1),
+            (" US ", "US", 1),
+            ("eu", "EU", None),
+        ):
+            with self.subTest(stamp=stamp):
+                row = self._row({"region": stamp})
+                self.assertEqual(
+                    (row["region"], row.get("member_count")), (region, count)
+                )
+
+    @override_settings(REGION="us")
+    def test_this_deployments_region_is_compared_without_case(self) -> None:
+        row = self._row({"region": "US"})
+        self.assertEqual((row["region"], row["member_count"]), ("US", 1))
+
+    def test_metadata_that_is_not_a_dict_counts_as_unstamped(self) -> None:
+        for metadata in (None, "EU", ["EU"]):
+            with self.subTest(metadata=repr(metadata)):
+                row = self._row(metadata)
+                self.assertEqual((row["region"], row["member_count"]), ("US", 1))
+                self.assertEqual(row["metadata"], metadata)
+
+    def test_this_regions_organisation_with_no_data_here(self) -> None:
+        row = self._row({"region": "US"}, org_id="org-x")
+        self.assertEqual(row["region"], "US")
+        self.assertNotIn("member_count", row)
+        self.assertNotIn("role", row)
+
+    def test_mixed_list_keeps_order_and_queries(self) -> None:
+        _org("org-b", "Org B")
+        orgs = [
+            CloudOrg(id="org-a", display_name="A", name="a", metadata={"region": "EU"}),
+            CloudOrg(id="org-b", display_name="B", name="b", metadata=None),
+            CloudOrg(id="org-x", display_name="X", name="x", metadata={"region": "US"}),
+        ]
+        with self.assertNumQueries(2):
+            rows = with_member_details(orgs, self.caller)
+        self.assertEqual(
+            [
+                (r["id"], r.get("region"), r.get("member_count"), r.get("role"))
+                for r in rows
+            ],
+            [
+                ("org-a", "EU", None, "admin"),
+                ("org-b", "US", 0, None),
+                ("org-x", "US", None, None),
+            ],
+        )