fix(ui-models): stop the shared hint contradicting a filled-in field

The line under the create form names the one blocked gate worth naming,
and its fallback arm reads "no models yet". An unmet Provider ID gate fell
through to that arm, so a card with two models listed right above it was
told it needed one. The key gate was already excluded for this reason; the
route gate was assumed excluded because its field explains itself, and was
not.

Tightening the route rule in the previous commit is what made this easy to
hit — a digit-leading id now fails the gate — but the fallthrough predates
it and fires for an empty or taken id just the same.

packages/client/ui-models/tests/provider-form.spec.tsx

@@ -790,6 +790,26 @@ describe('hand-declared providers', () => {
     expect(onClose).toHaveBeenCalledWith(true)
   })
 
+  it('never contradicts a filled-in field with the next gate\u2019s copy', () => {
+    mountCard()
+    const routeField = screen.getByLabelText(en.customRoute)
+    fireEvent.change(routeField, { target: { value: '2' } })
+    fireEvent.change(screen.getByLabelText(en.baseUrl), { target: { value: 'https://acme.test/v1' } })
+    fireEvent.click(screen.getByRole('button', { name: en.addModel }))
+    fireEvent.change(screen.getByLabelText(`${en.modelId} 1`), { target: { value: 'm' } })
+
+    // The route field explains itself right under the input; the shared line
+    // must stay silent rather than falling through to "no models yet" while
+    // the list above plainly has one.
+    expect(screen.getByText(en.customRouteInvalid)).toBeTruthy()
+    expect(screen.queryByText(en.customNeedsModels)).toBeNull()
+
+    // Fixing the route hands the line back to the gate that is actually unmet.
+    fireEvent.change(routeField, { target: { value: 'acme' } })
+    expect(screen.queryByText(en.customNeedsModels)).toBeNull()
+    expect(buttonNamed(en.create).disabled).toBe(false)
+  })
+
   it('refuses a route id whose derived credential reference would be illegal', () => {
     mountCard()
     const routeField = screen.getByLabelText(en.customRoute)