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/ui-slash/src/client/controller.ts

@@ -290,7 +290,16 @@ export class SlashController {
     const rolls = new Map<TriggerChar, readonly string[]>()
     for (const src of this.deps.roster.all()) {
       if (src.lexicon === undefined) continue
-      const names = src.lexicon(projection)
+      let names: readonly string[] | undefined
+      try {
+        names = src.lexicon(projection)
+      } catch (error) {
+        // A faulty source drops silently with a console record (the
+        // candidate-fetch failure policy); the refresh runs inside
+        // notification callbacks, where a throw would starve other consumers.
+        console.error(`[ui-slash] source "${src.name}" lexicon failed:`, error)
+        continue
+      }
       if (names === undefined) continue
       const prev = rolls.get(src.trigger)
       rolls.set(src.trigger, prev === undefined ? names : [...prev, ...names])

packages/client/ui-slash/src/client/service.ts

@@ -50,7 +50,16 @@ export class SlashService extends Service implements SlashServiceContract {
       throw new Error(`slash source "${src.trigger}${src.name}" is already registered`)
     }
     live.sources.push(src)
-    for (const controller of live.controllers.values()) controller.sourceAdded(src)
+    for (const controller of live.controllers.values()) {
+      try {
+        controller.sourceAdded(src)
+      } catch (error) {
+        // Contain faulty source callbacks (warm/subscribeLexicon): the
+        // registration must stand with a usable disposer and the remaining
+        // controllers must still be notified.
+        console.error(`[ui-slash] source "${src.trigger}${src.name}" late-registration setup failed:`, error)
+      }
+    }
     return () => {
       const at = live.sources.indexOf(src)
       if (at < 0) return