[DPE-10454] Use better status instead of blocked for transient update failures (#1795)

* [DPE-10454] Use better status instead of blocked for transient update failures

Use maintenance/waiting status instead of blocked one.

The 'failed to update cluster members on member' BlockedStatus was
misleading: these are transient, self-recovering conditions (a RetryError
from update_config(), or a peer IP not yet published) rather than states
needing operator intervention. Replace them with MaintenanceStatus /
WaitingStatus and a 'updating cluster members' message.

Update test_on_peer_relation_changed accordingly, and set an explicit
BlockedStatus before exercising the early-exit guard so that path stays
covered.

Assisted-by: Claude:claude-5-fable

* [DPE-10454] Apply comments from review

Author: taurus-forever

src/charm.py

@@ -1254,7 +1254,7 @@ def _on_peer_relation_changed(self, event: HookEvent):
             # Update the members of the cluster in the Patroni configuration on this unit.
             self.update_config()
         except RetryError:
-            self.set_unit_status(BlockedStatus("failed to update cluster members on member"))
+            self.set_unit_status(MaintenanceStatus("cluster member update failed, retrying"))
             return
         except ValueError as e:
             self.set_unit_status(BlockedStatus("Configuration Error. Please check the logs"))
@@ -1473,9 +1473,9 @@ def add_cluster_member(self, member: str) -> None:
             try:
                 self.update_config()
             except RetryError:
-                self.set_unit_status(BlockedStatus("failed to update cluster members on member"))
+                self.set_unit_status(MaintenanceStatus("cluster member update failed, retrying"))
         else:
-            self.set_unit_status(BlockedStatus("failed to update cluster members on member"))
+            self.set_unit_status(WaitingStatus("waiting for peer IP"))
 
     def _get_unit_ip(self, unit: Unit, relation_name: str = PEER_RELATION) -> str | None:
         """Get the IP address of a specific unit.

tests/unit/test_charm.py

@@ -2246,11 +2246,12 @@ def test_on_peer_relation_changed(harness):
         _update_config.assert_called_once()
         _start_patroni.assert_not_called()
         _update_new_unit_status.assert_not_called()
-        assert isinstance(harness.model.unit.status, BlockedStatus)
+        assert isinstance(harness.model.unit.status, MaintenanceStatus)
 
         # Test event is early exiting when in blocked status.
         _update_config.side_effect = None
         _member_started.return_value = False
+        harness.model.unit.status = BlockedStatus()
         harness.charm._on_peer_relation_changed(mock_event)
         _start_patroni.assert_not_called()
 
@@ -2524,12 +2525,11 @@ def test_add_cluster_member(harness):
         _update_config.assert_called_once_with()
         _update_config.reset_mock()
 
-        # Charm blocks when update_config fails
+        # Charm goes into maintenance when update_config fails
         _update_config.side_effect = RetryError(last_attempt=None)
         harness.charm.add_cluster_member("postgresql-0")
         _update_config.assert_called_once_with()
-        assert isinstance(harness.charm.unit.status, BlockedStatus)
-        assert harness.charm.unit.status.message == "failed to update cluster members on member"
+        assert isinstance(harness.charm.unit.status, MaintenanceStatus | WaitingStatus)
         _update_config.reset_mock()
 
         # Not ready error if not all members are ready