feat(ui): a note's check is editable, dated and sweepable (#3167, milestone 317 step 4)

Rule 27: no UI, no ship. Three surfaces.

THE EDITOR ASKS, but only where the answer can be saved: the fields appear
for a plain note and not for a task or a snippet, matching the service gate
from step 2 so the form never offers a write the save would reject. The
labels are phrased as the QUESTION rather than the field name — "how would
someone check this is still true?" and, underneath, "could this become false
without anyone editing it?". "Verify with" gets filled in on every note; the
question gets filled in on the few that can go stale. `expires_when` appears
only once a check exists, and asks for a state rather than a date in the
placeholder itself.

THE NOTE SHOWS ITS AGE beside the field — "checked 2026-08-28" or "never
checked", italic, and nothing at all when no check exists. No red/amber ramp,
matching RuleSweepPane: a colour scale would restate the sweep's ordering and
force an invented staleness threshold. "Never" is marked because it is
categorically different from a date, not a worse one.

THE SWEEP is a pane in the Knowledge view, not beside the rules sweep —
operator's call, taken over a unified "everything due" surface and over a
second pane under /rules. Notes stay where notes live. The cost, accepted
knowingly: no single screen shows every unconfirmed record. It REPLACES the
feed rather than filtering it, because a facet answers "show me this kind"
and this answers "show me what nobody has confirmed" — a question the type
chips cannot narrow without under-reporting.

Two REST routes for it, since step 3 built only the service and the MCP door.

Along the way: NoteEditorView spelled its write payload out at three call
sites (save, create, auto-save), so every new field had to be added three
times — which is how one of them ends up not carrying it. Now one `payload()`
and one `snapshot()`.

Known and filed, not fixed: NoteSweepPane copies ~12 scoped CSS rules from
RuleSweepPane (#3207). The clean extraction needs prefixed names, because
`.age`, `.row-title`, `.lede` and `.actions` all exist scoped in other
components and an unscoped global would leak into them — which means editing
the shipped rules sweep, blind, inside a step whose acceptance is the
operator looking at a different surface.

frontend/src/views/KnowledgeView.vue

@@ -4,6 +4,7 @@ import { useRouter } from "vue-router";
 import { apiGet } from "@/api/client";
 import type { TaskKind, TaskStatus, TaskPriority } from "@/types/note";
 import KindBadge from "@/components/KindBadge.vue";
+import NoteSweepPane from "@/components/NoteSweepPane.vue";
 import StatusBadge from "@/components/StatusBadge.vue";
 import PriorityBadge from "@/components/PriorityBadge.vue";
 import GraphView from "@/views/GraphView.vue";
@@ -13,6 +14,7 @@ import {
   Workflow,
   Search,
   Share2,
+  ShieldCheck,
   ChevronLeft,
   ChevronRight,
   X,
@@ -67,6 +69,13 @@ const FACET_CHIPS: [Exclude<Facet, "">, string][] = [
   ["process", "Processes"],
 ];
 
+// ─── View mode ────────────────────────────────────────────────────────────────
+// The sweep is cross-cutting — a note that has gone false does not care which
+// facet it sits under — so it REPLACES the browse list rather than filtering
+// it. Filtering would mean the answer depended on which chip was active, which
+// is the under-reporting the sweep exists to prevent (milestone 317 step 4).
+const sweepActive = ref(false);
+
 // ─── Filter state ─────────────────────────────────────────────────────────────
 
 const activeType = ref<Facet>("");
@@ -263,6 +272,10 @@ function onSearchInput() {
 }
 
 watch([activeType, sortMode], () => resetAndReobserve());
+// Closing the sweep remounts the feed, and with it the scroll sentinel — a
+// fresh element the old observer is not watching. Without this the list loads
+// its first page and then never loads another.
+watch(sweepActive, (open) => { if (!open) resetAndReobserve(); });
 watch(activeTag, () => { fetchCounts(); resetAndReobserve(); });
 
 // ─── Today bar ────────────────────────────────────────────────────────────────
@@ -471,6 +484,15 @@ onUnmounted(() => {
             <Share2 :size="16" />
             Graph
           </button>
+          <button
+            class="btn-ghost btn-compact"
+            :class="{ active: sweepActive }"
+            title="Notes that assert a fact about something outside your control, least-recently-confirmed first. Most notes are decisions and never appear."
+            @click="sweepActive = !sweepActive"
+          >
+            <ShieldCheck :size="16" />
+            Due
+          </button>
           <button
             class="btn-ghost btn-compact"
             :disabled="dupLoading"
@@ -481,6 +503,12 @@ onUnmounted(() => {
           </button>
         </div>
 
+        <!-- The sweep replaces the feed. It is not a facet: a facet answers
+             "show me this kind", and this answers "show me what nobody has
+             confirmed" — a question the type chips cannot narrow without
+             under-reporting it. -->
+        <NoteSweepPane v-if="sweepActive" @open-note="(id) => router.push(`/notes/${id}`)" />
+
         <!-- Near-duplicate report. A proposal surface only: unlike snippets
              (which merge losslessly), notes are never merged — the right fix is
              supersession, extraction into a reference note, or leaving parallel
@@ -518,6 +546,12 @@ onUnmounted(() => {
           </template>
         </div>
 
+        <!-- The whole feed stands down while the sweep is open: two answers
+             to two different questions on one screen is neither. Wrapped
+             rather than given an extra v-if branch, because the scroll
+             sentinel lives inside the grid and the observer must not be left
+             holding a ref to something that never renders. -->
+        <template v-if="!sweepActive">
         <!-- Loading / empty -->
         <div v-if="loading && items.length === 0" class="knowledge-empty">Loading…</div>
         <div v-else-if="!loading && items.length === 0" class="knowledge-empty">
@@ -591,6 +625,7 @@ onUnmounted(() => {
             <span v-if="contentFetching" class="sentinel-loading">Loading…</span>
           </div>
         </div>
+        </template>
       </div>
 
       <!-- Graph panel -->