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/sessions-service.spec.ts

@@ -35,6 +35,7 @@ type FeedRow = {
   origin?: 'subagent'
   running?: boolean
   blank?: boolean
+  agentPreset?: string
 }
 
 async function feedList(b: Bench, rows: FeedRow[]): Promise<void> {
@@ -44,6 +45,7 @@ async function feedList(b: Bench, rows: FeedRow[]): Promise<void> {
       ...(r.cwd !== undefined ? { cwd: r.cwd } : {}),
       ...(r.parentId !== undefined ? { parentSessionId: sid(r.parentId) } : {}),
       ...(r.origin !== undefined ? { origin: r.origin } : {}),
+      ...(r.agentPreset !== undefined ? { agentPreset: r.agentPreset } : {}),
     })),
   }) as never)
   await b.svc.refresh()
@@ -70,6 +72,21 @@ describe('list store projection', () => {
     expect(state.byId[sid('s2')]?.title).toBeUndefined()
   })
 
+  it('reprojects a blank session whose composition switched and nothing else moved', async () => {
+    const b = bench()
+    await feedList(b, [{ id: 's1', blank: true, agentPreset: 'standard' }])
+    expect(b.svc.list.getSnapshot().byId[sid('s1')]?.agentPreset).toBe('standard')
+
+    // A confirmed switch moves the preset alone: the row keeps its updatedAt,
+    // title, running, and blank bits, so an identity guard blind to the preset
+    // would serve the old row forever — and every reader (the hero chip's own
+    // no-op check, the header label) would keep the composition it replaced.
+    b.svc.noteAgentPreset(sid('s1'), 'minimal')
+    await Promise.resolve()
+
+    expect(b.svc.list.getSnapshot().byId[sid('s1')]?.agentPreset).toBe('minimal')
+  })
+
   it('reflects live increments (host stream via manager) into the store', async () => {
     const b = bench()
     await feedList(b, [{ id: 's1' }])

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