fix(web): follow a blank session's preset switch in the slash catalog

Presets own the rows that decide what a session's `/` menu contains, but
both browser catalogs cache per session and had no invalidation edge for a
recompose: `commands/changed` is registry-wide and recomposing registers
nothing, so the menu kept serving the composition the session no longer ran.

The host stream now frames the logged `agent-preset/selected` commit as
`host/session-preset-changed`; the runtime bridges it to the typed
`session/preset-changed` event, `ui-command` soft-refreshes that session's
directory key and `ui-skill` invalidates its catalog entry.

Reaching the host on a second switch was a separate defect: the list-row
identity guard compared every summary field except `agentPreset`, and the
merge keeps the row's `updatedAt`, so a switched row looked unchanged and
served its cached instance forever. The hero chip compares the pick against
that row, so switching back to the creation-time preset sent no RPC at all.

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

@@ -124,6 +124,11 @@ export class CommandService extends Service implements CommandServiceContract {
       warm: (session) => { this.directory.warm(session.sessionId) },
     }), 'command: slash source')
     ctx.on('commands/changed', () => { this.directory.invalidateAll() })
+    // A preset switch changes which commands ONE session's agent resolves and
+    // registers nothing globally, so the registry-wide signal above never
+    // fires for it: repull that key alone, soft, so the old snapshot serves
+    // the menu until the new one lands.
+    ctx.on('session/preset-changed', (sessionId) => { void this.directory.refresh(sessionId) })
     ctx.on('connection/reset', () => { this.directory.resetConnected() })
   }