docs(charm): trim storage-detaching comments and fix copyright year

Match the one-liner docstring density of the surrounding handlers instead
of an 8-line block (the why lives in the commit that added the guard),
and date the new test file 2026 (it was copied as 2025).

Signed-off-by: Marcelo Henrique Neppel <marcelo.neppel@canonical.com>

Author: marceloneppel

src/charm.py

@@ -2568,24 +2568,13 @@ def _install_snap_package(
             raise
 
     def _on_storage_detaching(self, _) -> None:
-        """Release the storage so Juju can unmount it on unit teardown.
-
-        Only act when the whole application is going away (``planned_units == 0``,
-        i.e. remove-application/destroy-model), which is where the storage unmount
-        actually hangs. On scale-down the surviving units still need this unit's
-        Patroni reachable to remove it from the raft cluster, so stopping the
-        workload here would break primary election.
-
-        ``storage-detaching`` runs before ``stop``, so this is the earliest hook
-        where the snap services and background processes that keep the storage
-        mounts busy can be stopped.
-        """
+        """Stop the workload so Juju can unmount the storage on app teardown."""
+        # On scale-down the surviving cluster still needs this unit's Patroni to
+        # remove it from raft; only stop when the whole app is going away.
         if self.app.planned_units() > 0:
             return
         self._observer.stop_observer()
         self._rotate_logs.stop_log_rotation()
-        # Stop every charmed-postgresql snap service (PostgreSQL, pgBackRest, the
-        # exporters) so the snap releases the storage mounts before Juju unmounts them.
         try:
             snap.SnapCache()[charm_refresh.snap_name()].stop()
         except snap.SnapError:

tests/integration/test_storage_detaching.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# Copyright 2025 Canonical Ltd.
+# Copyright 2026 Canonical Ltd.
 # See LICENSE file for licensing details.
 
 import logging
@@ -11,11 +11,8 @@
 
 logger = logging.getLogger(__name__)
 
-# rootfs (machine-scoped) storage is the issue's scenario. It matters:
-# - Juju 3.6 masks the bug via a cleanup_storage shortcut that removes still-Dying
-#   storage, so this only reproduces on Juju 4.0 (see tests/spread/.../task.yaml).
-# - On 4.0 the detachable ``lxd`` pool lets Juju destroy the container before
-#   detaching, so only ``rootfs`` reproduces the stuck unmount.
+# rootfs (machine-scoped) is the only pool that reproduces the stuck unmount on
+# Juju 4.0: the detachable lxd pool destroys the container before detaching.
 ROOTFS_STORAGE = dict.fromkeys(("archive", "data", "logs", "temp"), "rootfs")
 
 
@@ -24,12 +21,8 @@ def test_storage_released_on_removal(juju: JujuFixture, charm):
     """Graceful removal must release the storage so teardown completes.
 
     Regression test for canonical/postgresql-operator#1550: without stopping the
-    workload in the ``storage-detaching`` hook the charmed-postgresql snap keeps the
-    storage mounts busy, so Juju's unmount fails ("target is busy") and the unit,
-    storage and machine removal hangs forever.
-
-    Pinned to Juju 4.0 with rootfs storage by its spread task. ``force=True`` is
-    required because the charm still declares ``assumes: juju < 4``.
+    workload in the ``storage-detaching`` hook the snap keeps the storage mounts
+    busy, so Juju's unmount fails ("target is busy") and teardown hangs.
     """
     juju.ext.model.deploy(
         charm,

tests/spread/test_storage_detaching.py/task.yaml

@@ -1,9 +1,8 @@
 summary: test_storage_detaching.py
 environment:
   TEST_MODULE: test_storage_detaching.py
-  # #1550 only reproduces on Juju 4.0: 3.6 masks it via a cleanup_storage shortcut
-  # that removes still-Dying storage. Pin this task to a 4.0 variant and drop the
-  # default juju36 variant so it runs ONLY on 4.0 (the rest of the suite stays 3.6).
+  # #1550 only reproduces on Juju 4.0 (3.6 masks it by removing still-Dying storage),
+  # so pin this task to a juju40 variant and drop the default juju36.
   CONCIERGE_JUJU_CHANNEL/juju40: 4.0/stable
 variants:
   - -juju36