test(native-chat): retire the subagent-visibility guards now the roster renders

Two tests from the sibling item-coverage PR asserted that subagent items stay
on the generic gray row, explicitly gated on "until a real renderer exists".
This branch is that renderer, so both guards fire on merge — the handoff they
were written to mark rather than a regression.

They now pin the other side of it: subAgentActivity is suppressed because the
spawn-group roster renders it, and collabAgentToolCall deliberately stays
visible, since nothing guarantees a session reports subagent work as
subAgentActivity at all.

Git merged both files without conflict; only running the suite surfaced this.

src/main/codex/codex-structured-item-translation.test.ts

@@ -784,7 +784,7 @@ describe('codex item bodies', () => {
     }
   })
 
-  it('leaves subagent items on the generic row until a real renderer exists', () => {
+  it('drops the raw subagent item now the roster row renders it', () => {
     expect(
       codexJournalItem({
         type: 'subAgentActivity',
@@ -793,10 +793,7 @@ describe('codex item bodies', () => {
         agentThreadId: 'thread-child',
         agentPath: '/root/list_directory'
       })
-    ).toMatchObject({
-      handled: false,
-      body: { kind: 'status', providerFrame: { kind: 'item:subAgentActivity' } }
-    })
+    ).toMatchObject({ handled: true, body: null })
   })
 
   it('drops the sleep item, which codex itself renders as nothing', () => {

src/main/native-chat/agent-session-wire/provider-frame-disposition.test.ts

@@ -125,7 +125,7 @@ describe('provider frame classification catalog', () => {
     )
   })
 
-  it('keeps subagent items visible — the only evidence a spawned agent is working', () => {
+  it('suppresses subAgentActivity once the roster renders it, but never collabAgentToolCall', () => {
     expect(
       classifyProviderFrame('codex', 'item:subAgentActivity', {
         id: 'a-1',
@@ -133,7 +133,9 @@ describe('provider frame classification catalog', () => {
         agentThreadId: 'thread-child',
         agentPath: '/root/list_directory'
       })
-    ).toBe('timeline-substantive')
+      // The spawn-group roster row renders this now, so a raw gray row beside it
+      // would duplicate it. Suppressing it was gated on that renderer existing.
+    ).toBe('status-chrome')
     expect(
       classifyProviderFrame('codex', 'item:collabAgentToolCall', {
         id: 'c-1',