docs,test: settle review follow-ups for the create-by-name deletion

Rewrite the three sibling Agent Note pairs that still described create-by-name
as current (workspace-ui-product-flow, session-list-browsing-and-manual-order,
same-basename-workspace-adoption) and the one-route note's own alternative and
section title; delete scripts/hero-composer-dom-continuity.mjs, which drove the
name dialog removed by the one-route change; mark WorkspaceRegistry.create's
now test-only title parameter with a deletion TODO; pin the retired { name }
spelling as a schema rejection; align the workspace spec on stageDir and the
fixture spec title on path creates.

packages/host/apiproxy/tests/api-proxy-workspace.spec.ts

@@ -252,8 +252,7 @@ describe('host.openPath', () => {
 describe('workspace.create', () => {
   it('serializes concurrent creates of one path into a single registration', async () => {
     const { api, root } = await harness()
-    const target = join(root, 'alpha')
-    mkdirSync(target)
+    const target = stageDir(root, 'alpha')
     const responses = await Promise.all([
       api.workspace.create(request({ path: target })),
       api.workspace.create(request({ path: target })),
@@ -269,8 +268,7 @@ describe('workspace.create', () => {
 
   it('adopts only existing directories', async () => {
     const { api, root } = await harness()
-    const existing = join(root, 'existing')
-    mkdirSync(existing)
+    const existing = stageDir(root, 'existing')
     const first = expectOk(await api.workspace.create(request({ path: existing })))
     const repeated = expectOk(await api.workspace.create(request({ path: existing })))
     expect(first).toMatchObject({ created: true, workspace: { path: existing, title: 'existing' } })

packages/host/apiproxy/tests/rpc-schemas.spec.ts

@@ -327,6 +327,8 @@ describe('workspace domain schemas', () => {
   it('create requires a path', () => {
     expect(workspaceCreateRequestSchema.parse({ path: '/p' }).path).toBe('/p')
     expect(() => workspaceCreateRequestSchema.parse({})).toThrow()
+    // The retired create-by-name spelling stays a clean schema rejection.
+    expect(() => workspaceCreateRequestSchema.parse({ name: 'n' })).toThrow()
     expect(workspaceCreateValueSchema.parse({ workspace: view, created: false }).created).toBe(false)
   })