Expire trash after 30 days, and make the deadline something you can see

Trash had no end. A note sat in /trash until someone emptied it by hand, and
its attachment BYTES sat on disk the whole time — the pile-up the operator
asked about. Nothing purged; there was no scheduler at all.

Retention is server-owned: `trash_retention_days` (default 30, 0 = keep
forever) in the settings registry, so it lands in admin Settings with no
migration and takes effect without a restart. A background sweep started in
before_serving does the work. Clients learn about a purge the way they learn
about any deletion — as a tombstone on the delta feed.

An auto-purge nobody can see coming is data loss on a timer, so the window is
now visible: /api/config publishes it, notes carry `deleted_at`, Trash leads
with the policy, and each card counts down. The countdown rounds DOWN — saying
"1 day left" for a note with ten minutes on the clock is the one error here
that actually costs someone a note.

Three things this turned up on the way:

- `DELETE /api/notes/<id>` hard-deleted the row, leaving no tombstone at all.
  A permanent delete in the web UI never reached a linked device, which would
  keep its copy forever and push it back on the next edit. It now purges
  through the same path as everything else.
- The purge left `note_revisions` and `note_link_previews` behind. A revision
  holds the full body, so the text of a "permanently deleted" note was still
  sitting in the database.
- `deleted_at` now SURVIVES a purge instead of being cleared. It's still true,
  and it means every query that says "not trashed" excludes tombstones for
  free — without it a content-less row reads as a perfectly normal active note
  and shows up on the board as a blank card.

Desktop keeps its own clock only when there's nobody else to keep one: the
sweep runs at startup on an UNLINKED device and refuses otherwise. A linked
client that expired notes on its own schedule could destroy something the
server was deliberately keeping, then push that delete upstream. Local policy
must never outrank the server's — so it also adopts the server's window for
the countdown rather than showing its offline default.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SreJkbxB4gx8pPsu8QbLPi

frontend/src/views/BoardView.vue

@@ -2,6 +2,7 @@
 import { computed, onBeforeUnmount, onMounted, ref, watch } from "vue";
 import { useRoute, useRouter } from "vue-router";
 import { useNotesStore, type Note, type NoteView } from "../stores/notes";
+import { useConfigStore } from "../stores/config";
 import { useUiStore } from "../stores/ui";
 import { facetCount, facetsFromQuery, facetsToQuery } from "../notes/facets";
 import { useNoteEditor } from "../composables/useNoteEditor";
@@ -12,6 +13,7 @@ import NoteCard from "../components/NoteCard.vue";
 import NoteEditor from "../components/NoteEditor.vue";
 
 const notes = useNotesStore();
+const config = useConfigStore();
 const route = useRoute();
 const ui = useUiStore();
 const router = useRouter();
@@ -144,6 +146,17 @@ watch(
 );
 watch([currentView, currentLabel, facetKey], () => (focusedIndex.value = -1));
 
+// The retention policy, said out loud at the top of Trash. Empty when retention is
+// off — promising a deletion that never comes is its own kind of lie.
+const retentionNotice = computed(() => {
+  if (currentView.value !== "trash") return "";
+  const days = config.trashRetentionDays;
+  if (days <= 0) return "Notes stay in Trash until you delete them.";
+  return days === 1
+    ? "Notes here are permanently deleted 1 day after you trash them. Restore one to keep it."
+    : `Notes here are permanently deleted ${days} days after you trash them. Restore one to keep it.`;
+});
+
 const emptyState = computed(() => {
   if (filtered.value) return { title: "No notes match these filters", subtitle: "Try clearing or loosening a facet." };
   if (currentView.value === "trash") return { title: "Trash is empty", subtitle: "Notes you delete land here first." };
@@ -208,6 +221,13 @@ async function onDrop(target: Note) {
     </button>
     <FilterBar v-if="isMainBoard" />
 
+    <p
+      v-if="retentionNotice"
+      class="mx-auto mb-4 max-w-xl rounded-xl bg-black/5 px-4 py-2.5 text-center text-sm text-neutral-600 dark:bg-white/10 dark:text-neutral-300"
+    >
+      {{ retentionNotice }}
+    </p>
+
     <AsyncState
       :loading="notes.loading"
       :error="loadError || undefined"