feat(events): one lease and the participation verbs (Phase 11b)

The UO half of protocol 6 part b. No route added, no schema change, no
MODULE_API bump.

`uo.playercaps.skillcap` is the one lease, and the catalog is short because
ServUO made it short: of the 158 non-Bridge `Config.Get` call sites in
`Scripts/`, roughly eight are read live. This one is read inside
`CharacterCreation.cs`'s per-character path, so it is both live and observable --
which is what "proven" has to mean, since the failure an allowlist exists to
prevent is a key that applies cleanly and changes nothing.

Its `apply()` sends a DURATION rather than the deadline: an absolute time
computed here and honoured there is measured against two clocks, and a shard
running ten minutes fast would restore a ten-minute lease the instant it took it.
Its `restore()` turns `lease.drifted` into `{ drifted: true, current }` rather
than an error, because core records drift as a distinct successful outcome and an
error would put the row on the retry ladder. Its `inForce()` asks whether the
shard still HOLDS the lease, never whether the value still matches -- see the
core PR.

`uo.participation.open` / `.collect` count who took part and file them on the
success envelope. `open` is the one resource in this module that must NOT
reconcile by boot stamp: every other resource here lives in shard memory, so a
changed bootId IS the proof it is gone, while the participation ledger is written
into the world save precisely so it survives that restart. It asks instead.

Co-Authored-By: Claude <noreply@anthropic.com>

server/utils/uoLinkClient.js

@@ -223,6 +223,72 @@ const adminUnban = ({ actor, account }) =>
 const adminBroadcast = ({ actor, text, hue, idempotencyKey }) =>
   call('/admin/broadcast', { method: 'POST', body: { actor, text, hue, idempotencyKey } })
 
+// ── The event plane (protocol 6, EVENTS_PLAN.md Phase 11b) ─────────────────
+//
+// Leases and the run-scoped participation ledger. Both are gated on the shard by
+// `Bridge.EventsEnabled`, which is deliberately NOT the admin plane's switch: an
+// operator consenting to staff moderation from a screen has not thereby consented
+// to the website changing their world on a schedule at four in the morning. A
+// shard with the plane off answers 403, and the actions turn that into a refusal
+// an author can read rather than a retry.
+
+// Every lease this shard offers, with what each is worth right now and what is
+// holding it. One read serves both questions core asks — `read()` wants the
+// current value, `inForce()` wants to know whether the shard still has a record
+// of the hold — so a lease costs one round trip, not two.
+const getLeases = () => call('/lease')
+
+// `holdMs` is authoritative and `untilMs` is display only. An absolute deadline
+// computed here and honoured there is a deadline measured against two clocks, and
+// a shard running ten minutes fast would restore a ten-minute lease the moment it
+// took it. Values cross as TEXT whatever the lease's declared type: `1200` and
+// `1200.0` are one number to a JSON parser and two strings to a compare-and-set.
+const applyLease = ({ key, value, holdMs, untilMs, runId, idempotencyKey }) =>
+  call('/lease', {
+    method: 'POST',
+    body: { key, value: String(value), holdMs, untilMs, runId, idempotencyKey },
+  })
+
+// `expected` is what this run applied and `baseline` is what to put back, both out
+// of core's ledger rather than the shard's memory — so a release still works after
+// a reconnect, and a shard that has forgotten the lease entirely (a restart, which
+// reverts every config lease by design) answers honestly instead of refusing.
+const releaseLease = ({ key, expected, baseline, idempotencyKey }) =>
+  call('/lease/release', {
+    method: 'POST',
+    body: {
+      key,
+      expected: expected == null ? undefined : String(expected),
+      baseline: baseline == null ? undefined : String(baseline),
+      idempotencyKey,
+    },
+  })
+
+// The participation ledger. The area is a map, a point and a radius rather than a
+// region name, because protocol 6's own walk established that the most specific
+// region containing an event is routinely anonymous.
+const openParticipation = ({ runId, map, x, y, radius, holdMs, idempotencyKey }) =>
+  call('/participation', {
+    method: 'POST',
+    body: { runId: String(runId), map, x, y, radius, holdMs, idempotencyKey },
+  })
+
+// A POST for a read, and the reason is the phase's headline: on a well-attended
+// run the shard walks its members across Core ticks rather than in one inbound
+// call, so a repeat arriving mid-walk is answered `bridge.busy` (425). A read that
+// can legitimately be refused as a repeat in flight is not a GET.
+const snapshotParticipation = ({ runId, idempotencyKey }) =>
+  call(`/participation/${encodeURIComponent(runId)}/snapshot`, {
+    method: 'POST',
+    body: { idempotencyKey },
+  })
+
+const closeParticipation = ({ runId, idempotencyKey }) =>
+  call(`/participation/${encodeURIComponent(runId)}/close`, {
+    method: 'POST',
+    body: { idempotencyKey },
+  })
+
 // ── Help-page (support) queue commands (§6) ────────────────────────────────
 const respondPage = (pageId, { message, close }) =>
   call(`/pages/${encodeURIComponent(pageId)}/respond`, { method: 'POST', body: { message, close } })
@@ -256,6 +322,12 @@ module.exports = {
   deleteTownCrier,
   postNews,
   deleteNews,
+  getLeases,
+  applyLease,
+  releaseLease,
+  openParticipation,
+  snapshotParticipation,
+  closeParticipation,
   adminKick,
   adminBan,
   adminUnban,