fix(rust): a zone resource carries its deadline as until (W1)

Stage 4 of docs/modules/rust/PLAN_LAST_FIXES.md, the module's half of W1.
A placed zone now reports `until`, reckoned from the answer as now plus
holdMs, so it lands a round trip after the game's own deadline and never
before it. Core's reconcile then files a zone gone past that deadline as
expired, where a reconnect used to log resource.orphaned five seconds
before the game's world.expired arrived. Crates and NPCs send no
holdMs, so they carry no until.

No core pin change: `until` has been in the resource contract all along,
and a core without the reconcile half only shows it on the console.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

server/eventWorld.js

@@ -324,11 +324,19 @@ async function place(server, send, body, what) {
   }
 
   const placed = Array.isArray(data.placed) ? data.placed : []
+  // A zone's deadline, as core's `until` (W1, PLAN_LAST_FIXES). The game erases
+  // the zone `holdMs` after it placed it; reckoned from the answer, on this
+  // clock, it lands a round trip after the game's, never before. With it core's
+  // reconcile files a zone gone past its deadline as expired instead of
+  // orphaned, which a reconnect used to show five seconds before the game's own
+  // `world.expired` arrived. Crates and NPCs have no deadline and send none.
+  const until = Number(body.holdMs) > 0 ? new Date(Date.now() + Number(body.holdMs)).toISOString() : null
   return {
     ok: true,
     resources: placed.map((row) => ({
       kind: OWNED_KIND,
       ref: refOf(server.id, row.id),
+      ...(until ? { until } : {}),
       payload: {
         serverId: server.id,
         what: row.kind,