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/tests/service.spec.ts

@@ -617,6 +617,30 @@ describe('directory invalidation events', () => {
     expect(source.matchSpace!(proj('s1'), '/goal')).toBeUndefined()
   })
 
+  it('session/preset-changed repulls the recomposed session and leaves the others served', async () => {
+    const rounds = new Map<SessionId, number>()
+    const { ctx, source, warm } = await bench({
+      commands: (payload) => {
+        const round = (rounds.get(payload.sessionId) ?? 0) + 1
+        rounds.set(payload.sessionId, round)
+        return Promise.resolve({
+          commands: round === 1
+            ? S1_CMDS
+            : [{ name: 'fresh', description: '', input: { hint: 'h' } }],
+        })
+      },
+    })
+    await warm(proj('s1'))
+    await warm(proj('s2'))
+    // A preset switch changes which commands one session's agent resolves;
+    // every other session keeps the catalog its own composition serves.
+    ctx.emit('session/preset-changed', sid('s1'), 'minimal')
+    await new Promise(resolve => setTimeout(resolve, 0))
+    expect(source.matchSpace!(proj('s1'), '/fresh')).not.toBeUndefined()
+    expect(source.matchSpace!(proj('s1'), '/goal')).toBeUndefined()
+    expect(source.matchSpace!(proj('s2'), '/goal')).not.toBeUndefined()
+  })
+
   it('connection/reset hard-drops every session key until its rewarm lands', async () => {
     let block = false
     let release!: (value: { commands: CommandDescriptor[] }) => void