docs(dashboard): document live countdown ticker for schedule next-fire and reminder due-at labels

Reminder due-at labels ("in 3m 45s") and schedule next-fire cells
were computed once at render time and never updated. For short-horizon
reminders the stale count was visually misleading.

Both renderers now stamp data-due-at=<unix> on their respective
elements (.reminder-due / .sched-due). A shared 1s setInterval
ticker walks all live elements and rewrites textContent using
fmtDuration / fmtAgo — same zero-re-render pattern as the
existing question TTL chip ticker.

docs/web-ui/dashboard.md

@@ -245,6 +245,13 @@ checked-not-originally-active = `targets_add`; submit PATCHes
 `/api/schedules/{id}`), and a `✕` button cancels the whole
 schedule (`POST /api/schedules/{id}/cancel`).
 
+The `next` column cell (`.sched-due`) carries a `data-due-at`
+Unix timestamp attribute; a shared 1s ticker rewrites it
+in-place showing `fmtDuration` while in the future and
+`overdue X ago` once the fire time has passed — same
+zero-re-render pattern as the reminder due-at labels and the
+question TTL chip.
+
 The table's last row is a permanent inline creation row:
 inputs live directly in table cells (targets as checkboxes,
 body textarea that expands on focus, datetime-local pre-filled
@@ -265,7 +272,12 @@ button hard-deletes (`POST /cancel-reminder/{id}`) and a
 `R3TRY` button re-arms one whose delivery failed
 (`POST /retry-reminder/{id}`). Backed by `GET /api/reminders`.
 Lives in the SCH3DUL3S tab alongside operator schedules so the
-operator has one place for everything time-fired.
+operator has one place for everything time-fired. The due-time
+label (`.reminder-due`) carries a `data-due-at` Unix timestamp
+attribute; a shared 1s ticker rewrites it in-place — showing
+`in Xm Ys` while the reminder is in the future and
+`overdue X ago` once the deadline passes — without triggering a
+full re-render of the list.
 
 ## P33RS tab
 

frontend/packages/dashboard/src/tabs.js

@@ -455,8 +455,7 @@ window.marked = marked;
       menuItem('↻ R3BU1LD', { action: '/rebuild/', confirm: `rebuild ${c.name}? hot-reloads the container.` }),
       menuSep(),
       // Deep-link to the AGENT log tab pre-filtered to this container.
-      // The ?agent= param is read by logs.js on load; the stored localStorage
-      // selection is overridden so the operator lands directly in this
+      // The ?agent= param is read by logs.js on load and pre-selects this
       // agent's journal without extra clicks.
       menuLink('journal logs →',
         `/logs.html?agent=${encodeURIComponent(c.name)}#agent`,
@@ -1999,6 +1998,11 @@ window.marked = marked;
   // a request pending for an hour could still show "0s ago" without
   // this ticker. Also flips `.stale` (amber highlight) at exactly 1h
   // rather than only at the next re-render.
+  // Live countdown for reminder due-at labels and schedule next-fire
+  // cells. Both renderers stamp `data-due-at` on the element so this
+  // single ticker keeps them fresh without triggering a full re-render.
+  // `.reminder-due` → "overdue X ago" / "in Y"
+  // `.sched-due`    → same pattern
   setInterval(() => {
     const now = Math.floor(Date.now() / 1000);
     document.querySelectorAll('.approval-ts[data-requested-at]').forEach((node) => {
@@ -2008,6 +2012,14 @@ window.marked = marked;
       node.textContent = 'requested ' + fmtAgo(requestedAt);
       node.classList.toggle('stale', ageSec >= 3600);
     });
+    document.querySelectorAll('.reminder-due[data-due-at], .sched-due[data-due-at]').forEach((node) => {
+      const dueAt = Number(node.getAttribute('data-due-at'));
+      if (!Number.isFinite(dueAt)) return;
+      const dueIn = dueAt - now;
+      node.textContent = dueIn <= 0
+        ? 'overdue ' + fmtAgo(dueAt)
+        : (node.classList.contains('reminder-due') ? 'in ' : '') + fmtDuration(dueIn);
+    });
   }, 1000);
 
   const APPROVAL_TAB_KEY = 'hyperhive:approvals:tab';
@@ -2790,7 +2802,11 @@ window.marked = marked;
           : `in ${fmtDuration(dueIn)}`;
         const head = el('div', { class: 'reminder-head' },
           el('span', { class: 'agent' }, r.agent), ' ',
-          el('span', { class: 'meta', title: new Date(r.due_at * 1000).toISOString() }, dueLabel),
+          el('span', {
+            class: 'meta reminder-due',
+            title: new Date(r.due_at * 1000).toISOString(),
+            'data-due-at': String(r.due_at),
+          }, dueLabel),
           ' ',
           el('span', { class: 'meta' }, `· id ${r.id}`),
         );
@@ -3393,6 +3409,8 @@ window.marked = marked;
       nextCell.textContent = dueIn <= 0
         ? 'overdue ' + fmtAgo(s.next_fire_at_unix)
         : fmtDuration(dueIn);
+      nextCell.classList.add('sched-due');
+      nextCell.dataset.dueAt = String(s.next_fire_at_unix);
     }
     tr.append(nextCell);