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/runtime/tests/wire-events.spec.ts

@@ -1,6 +1,7 @@
 /**
  * Wire-to-typed-event bridge: host/commands-changed
- * → ctx 'commands/changed'; each established connection generation →
+ * → ctx 'commands/changed'; host/session-preset-changed →
+ * ctx 'session/preset-changed'; each established connection generation →
  * ctx 'connection/reset' (the forced cache-invalidation broadcast).
  */
 import { Context } from 'cordis'
@@ -67,6 +68,17 @@ describe('wire event bridge', () => {
     ])
   })
 
+  it('broadcasts session/preset-changed with the recomposed session and its new preset', async () => {
+    const bench = await mount()
+    const seen: Array<[string, string]> = []
+    bench.ctx.on('session/preset-changed', (sessionId, agentPreset) => { seen.push([sessionId, agentPreset]) })
+    bench.sinks?.onHostEnvelope?.({
+      rpcId: 'r1' as never,
+      payload: { type: 'host/session-preset-changed', sessionId: 's1' as never, agentPreset: 'minimal' },
+    })
+    expect(seen).toEqual([['s1', 'minimal']])
+  })
+
   it('broadcasts connection/reset on every established generation (reconnect invalidation)', async () => {
     const bench = await mount()
     let resets = 0