fix(client): contain notification-callback failures and document the source lifecycle

Review follow-ups: the three new notify loops (currentProvideInfo
subscribers, ui-skill lexicon listeners, late-registration controller
setup) now contain per-callback failures so one faulty consumer cannot
starve the rest, abort the list projection pass, or poison the source
roster with no disposer; controller lexicon polling drops a throwing
source with a console record like the candidate path. The ui-slash
README (both languages) now states the late-registration warm and the
subscribeLexicon contract, and the scenario suite drives a typed /name
token gaining its decoration when the roll settles with no further
input.

packages/client/runtime/src/client/sessions/service.ts

@@ -275,7 +275,16 @@ export class SessionsService {
     const next = this.maybeProvideInfo(this.list.getSnapshot().current)
     if (next === this.currentProvideInfoSnapshot) return
     this.currentProvideInfoSnapshot = next
-    for (const fn of [...this.currentProvideInfoListeners]) fn()
+    for (const fn of [...this.currentProvideInfoListeners]) {
+      try {
+        fn()
+      } catch (error) {
+        // Contain subscriber failures: this notify runs inside the list
+        // notification, where a throwing render-side subscriber would starve
+        // later listeners and abort the projection pass that scheduled it.
+        console.error('sessions.currentProvideInfo subscriber failed:', error)
+      }
+    }
   }
 
   /** Build the static no-session kit and reject duplicate declared names. */