feat(events): send the idempotency key, and declare champ.boss.killed (Phase 11a)

The website's half of protocol 6.

Every event-driven write now carries the step's idempotency key, and `uo.broadcast`
stops being un-retryable. Phase 9 shipped it answering `retry: false` to everything
including a 503 from a shard that was merely restarting, with a comment naming the
line that would change when the wire could refuse a repeat. This is that line: it
defers to `sidecarFailure`, the same helper its two siblings already used, so the
hand-rolled variant that forced every outcome terminal is gone rather than re-tuned.

One verb was less idempotent than its own id made it look. Both keyed verbs post
under a run-scoped id and a repeat replaces — but `news.add` with `announce: true`
makes the criers proclaim the title on every post, so a retry replaced the article
silently and proclaimed it again. The key stops the second proclamation.

`champ.boss.killed` is mapped to the `champs` feature (rule 2 would otherwise fail
it closed to admin), with `damagers` a nested `staff` field rule: the kill is public
because a champion falling is what the board is for, the ranked roll of who was
strong enough to fell it is not. `uo.champ.boss_killed` is declared as a trigger —
which is what makes it usable as an event PHASE CONDITION, since a condition is
written over a trigger firing — and it carries `damagerCount`, never a damager name,
because a trigger variable reaches mail an operator may address to every subscriber.

Its seeded rule is its own group, `champ-boss-killed-v1`: `triggers-v1` is stamped
once under a settings guard, so appending a 27th entry would have reached fresh
installs and nothing else. It also ships email+inapp and NOT push, and the comment
says why — no trigger in this module is also a registered stream, so no engagement
rule here can push. That is pre-existing in twenty rules and flagged rather than
fixed; this one declines to be the twenty-first.

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

server/utils/shardVisibility.js

@@ -83,7 +83,27 @@ const FEATURES = {
   // ── Shipped before v3. Defaults reproduce the previous hardcoded behavior. ──
   status: { audience: 'anonymous', fields: {} },
   activity: { audience: 'anonymous', fields: {} },
-  champs: { audience: 'anonymous', fields: {} },
+  // Protocol 6 adds `champ.boss.killed` to this feature, and with it the first
+  // field on a champs frame that is about PEOPLE rather than about an altar.
+  //
+  // `damagers` is the ranked table of who fought the boss and for how much. It is
+  // the honest basis for "who slew the champion" and it is also a performance
+  // record of named players that nobody consented to publish, which is precisely
+  // the tension the ladder exists to let a shard resolve for itself. It defaults
+  // to `staff`: the kill is public (a champion falling is announced in-world and
+  // is the content the board is for), the roll of who did the damage is not. A
+  // shard that wants a public board lowers one rule.
+  //
+  // Nested for the same reason `market.fees` and `houses.schedule` are: one rule
+  // covers the whole table rather than a rule per column, and the columns here
+  // are actor objects whose `acct`/`webId` remain admin-only by the locked-field
+  // rule regardless of what this is set to.
+  //
+  // `killer` is deliberately NOT listed. It is the single actor whose blow landed
+  // last, it is announced in-game to everyone present, and it is the same shape
+  // and the same disclosure `mob.killed` has published on the public activity
+  // feed since before this framework existed.
+  champs: { audience: 'anonymous', fields: { damagers: 'staff' } },
   guilds: { audience: 'anonymous', fields: {} },
   governors: { audience: 'anonymous', fields: {} },
   // The public Houses page showed IDOC location only; owner/price were staff.
@@ -189,6 +209,10 @@ const KIND_FEATURE = new Map(
     // boards
     'champ.update': 'champs',
     'champ.remove': 'champs',
+    // Protocol 6. Without this line rule 2 would fail the new kind closed to
+    // admin-only — correct as a default, and wrong as an outcome: a champion
+    // falling is exactly what the public board is for.
+    'champ.boss.killed': 'champs',
     'guild.update': 'guilds',
     'guild.remove': 'guilds',
     'guild.join': 'guilds',