Address Copilot findings: whitespace-only schedule_id and typo

Copilot's remaining suppressed comments (2026-09-18 Lite review) on this
PR:

1. schedule_id validation in Subscriptions.create(), Subscriptions.update(),
   and RequestFactory.Subscription.create_req() relied on truthiness, which
   lets a whitespace-only id (e.g. " ") through to the wire layer and
   produces the same confusing error the None/empty checks exist to avoid.
   All three call sites now reject blank-after-strip ids explicitly.
2. Typo: "Susbcription" -> "Subscription" in create()'s no-item error.

The other two Copilot comments (ScheduleItem.from_element list-unwrap in
_parse_element, and the inline-schedule-with-no-id fallback) were already
fixed in a prior commit (1a423a9) on this branch before this pass started.

Adds regression tests for the whitespace-only schedule_id case at both the
endpoint and RequestFactory layers.

Co-Authored-By: Claude Code <noreply@anthropic.com>

Author: jacalata

tableauserverclient/server/endpoint/subscriptions_endpoint.py

@@ -41,12 +41,15 @@ def get_by_id(self, subscription_id: str) -> SubscriptionItem:
     @api(version="2.3")
     def create(self, subscription_item: SubscriptionItem) -> SubscriptionItem:
         if not subscription_item:
-            error = "No Susbcription provided"
+            error = "No Subscription provided"
             raise ValueError(error)
-        if not subscription_item.schedule_id:
+        if not (subscription_item.schedule_id or "").strip():
             # See tableau/server-client-python#1658: users trying to create an
             # "On Extract Refresh" subscription pass schedule_id=None and hit
-            # a confusing wire-layer error. Point them at the factory.
+            # a confusing wire-layer error. A whitespace-only id is the same
+            # failure in disguise -- it would still serialize and hit the
+            # same wire-layer error -- so reject it here too, not just None.
+            # Point them at the factory.
             raise ValueError(
                 "schedule_id is required; for on-extract-refresh subscriptions "
                 "use SubscriptionItem.on_extract_refresh(...)"
@@ -84,7 +87,7 @@ def update(self, subscription_item: SubscriptionItem) -> SubscriptionItem:
             schedule_id = subscription_item.schedule.id
             if schedule_id is not None:
                 subscription_item.schedule_id = schedule_id
-        if not schedule_id:
+        if not (schedule_id or "").strip():
             raise ValueError(
                 "schedule_id is required to update a subscription. On Tableau "
                 "Cloud, subscriptions parsed from a GET response may inline the "

tableauserverclient/server/request_factory.py

@@ -1356,14 +1356,15 @@ def create_req(self, xml_request: ET.Element, subscription_item: "SubscriptionIt
         # actionable error rather than the TypeError ElementTree raises when
         # attrib["id"] is set to None, and so python -O doesn't strip the
         # check entirely.
-        if subscription_item.schedule_id is None:
+        schedule_id = subscription_item.schedule_id
+        if schedule_id is None or not schedule_id.strip():
             raise ValueError(
                 "schedule_id is required to build a subscription create "
                 "request; for on-extract-refresh subscriptions use "
                 "SubscriptionItem.on_extract_refresh(...)"
             )
         schedule_element = ET.SubElement(subscription_element, "schedule")
-        schedule_element.attrib["id"] = subscription_item.schedule_id
+        schedule_element.attrib["id"] = schedule_id
 
         # User element
         user_element = ET.SubElement(subscription_element, "user")

test/test_subscription.py

@@ -132,6 +132,30 @@ def test_create_rejects_empty_schedule_id(server: TSC.Server) -> None:
         server.subscriptions.create(sub)
 
 
+def test_create_rejects_whitespace_only_schedule_id(server: TSC.Server) -> None:
+    """A whitespace-only schedule_id is the same failure mode as None/empty:
+    truthiness alone lets it through, but it would still serialize as
+    <schedule id="   "/> and hit the same confusing wire-layer error.
+    """
+    target = TSC.Target("view-id", "view")
+    sub = TSC.SubscriptionItem("subject", "   ", "user-id", target)
+    with pytest.raises(ValueError, match="on_extract_refresh"):
+        server.subscriptions.create(sub)
+
+
+def test_create_req_rejects_whitespace_only_schedule_id(server: TSC.Server) -> None:
+    """RequestFactory.Subscription.create_req must reject a whitespace-only
+    schedule_id too, for callers who bypass Subscriptions.create() and use
+    the factory directly.
+    """
+    from tableauserverclient.server.request_factory import RequestFactory
+
+    target = TSC.Target("view-id", "view")
+    sub = TSC.SubscriptionItem("subject", "   ", "user-id", target)
+    with pytest.raises(ValueError, match="schedule_id is required"):
+        RequestFactory.Subscription.create_req(sub)
+
+
 def test_subscription_defaults_refresh_extract_triggered_false(server: TSC.Server) -> None:
     """A default SubscriptionItem does not opt into extract-refresh triggering."""
     target = TSC.Target("view-id", "view")
@@ -223,6 +247,19 @@ def test_update_rejects_missing_schedule_id(server: TSC.Server) -> None:
         server.subscriptions.update(sub)
 
 
+def test_update_rejects_whitespace_only_schedule_id(server: TSC.Server) -> None:
+    """Same failure mode as None: a whitespace-only schedule_id would pass a
+    truthiness check and reach RequestFactory, still producing a confusing
+    wire-layer error. update() must reject it explicitly.
+    """
+    target = TSC.Target("view-id", "view")
+    sub = TSC.SubscriptionItem("subject", "sched-id", "user-id", target)
+    sub._id = "existing-sub-id"  # type: ignore[assignment]
+    sub.schedule_id = "   "
+    with pytest.raises(ValueError, match="schedule_id is required"):
+        server.subscriptions.update(sub)
+
+
 def test_update_req_emits_refresh_extract_triggered_when_true(server: TSC.Server) -> None:
     """When the flag is True, update_req must emit refreshExtractTriggered='true'."""
     from tableauserverclient.server.request_factory import RequestFactory