Add back-to-inventory header on infrastructure subviews

The connections-table flip in 00c6dc2dd removed the workspace's top-of-
page subtab strip but left the install panel and platforms workspace
rendering bare with no path back to the inventory table. Operators who
clicked Add a system, picked a platform, and landed on
/settings/infrastructure/install or /settings/infrastructure/platforms/*
had to leave Settings entirely and return to the tab to get back to the
table.

Render a persistent breadcrumb header above every non-inventory view
inside InfrastructureWorkspace: a "← Connections and Inventory" button
that navigates back to the bare /settings/infrastructure route, plus a
heading naming the current subview. Inventory itself is unchanged.

Bring agent-lifecycle rule 7 into line by requiring this back-to-
inventory affordance on every detail route under /settings/infrastructure
so deeper surfaces are never reachable without a visible return path.
Cover the new header on install and platforms subviews — and its absence
on the inventory landing — in InfrastructureWorkspace.test.tsx.

docs/release-control/v6/internal/subsystems/agent-lifecycle.md

@@ -371,10 +371,15 @@ an add-only capacity posture.
    `/settings/infrastructure/operations` remain reachable as detail routes
    for install, platform connections, and legacy reporting/control surfaces
    respectively, but the workspace shell must not gate inventory visibility
-   behind tab navigation. Read-only sessions must continue to redirect the
-   install detail route back to the unified inventory view and suppress the
-   add-system entry point on the base table so presentation-policy
-   restrictions still hold.
+   behind tab navigation. Every non-inventory detail route under
+   `/settings/infrastructure/*` must render a persistent breadcrumb header
+   that includes a one-click `Connections and Inventory` control returning
+   to the bare `/settings/infrastructure` route, so operators are never
+   stranded on a deeper install or platform-connection surface without a
+   visible path back to the unified table. Read-only sessions must continue
+   to redirect the install detail route back to the unified inventory view
+   and suppress the add-system entry point on the base table so
+   presentation-policy restrictions still hold.
 8. Keep post-install lifecycle completion explicit inside
    `frontend-modern/src/components/Settings/InfrastructureInstallerSection.tsx`
    and `frontend-modern/src/components/Settings/useInfrastructureInstallState.tsx`.

frontend-modern/src/components/Settings/InfrastructureWorkspace.tsx

@@ -1,4 +1,4 @@
-import { Component, Match, Switch, createEffect, createMemo, createSignal } from 'solid-js';
+import { Component, Match, Show, Switch, createEffect, createMemo, createSignal } from 'solid-js';
 import { useLocation, useNavigate } from '@solidjs/router';
 import { presentationPolicyIsReadOnly } from '@/stores/sessionPresentationPolicy';
 import { InfrastructureInstallPanel } from './InfrastructureInstallPanel';
@@ -57,8 +57,36 @@ export const InfrastructureWorkspace: Component<InfrastructureWorkspaceProps> =
     }
   });
 
+  const subviewHeading = createMemo(() => {
+    switch (activeView()) {
+      case 'install':
+        return 'Install on a host';
+      case 'platforms':
+        return 'Platform connections';
+      case 'operations':
+        return 'Reporting';
+      default:
+        return '';
+    }
+  });
+
   return (
     <div class="space-y-6">
+      <Show when={activeView() !== 'inventory'}>
+        <div class="flex items-center gap-2 text-sm">
+          <button
+            type="button"
+            onClick={() => navigate(buildInfrastructureWorkspacePath('inventory'))}
+            class="inline-flex items-center gap-1 rounded-md border border-border bg-surface px-2.5 py-1 text-muted hover:bg-surface-hover hover:text-base-content"
+          >
+            <span aria-hidden="true">←</span>
+            <span>Connections and Inventory</span>
+          </button>
+          <span class="text-muted" aria-hidden="true">/</span>
+          <span class="font-medium text-base-content">{subviewHeading()}</span>
+        </div>
+      </Show>
+
       <Switch>
         <Match when={activeView() === 'inventory'}>
           <ConnectionsTable

frontend-modern/src/components/Settings/__tests__/InfrastructureWorkspace.test.tsx

@@ -158,6 +158,37 @@ describe('InfrastructureWorkspace', () => {
     expect(screen.getByTestId('reporting-panel')).toBeInTheDocument();
   });
 
+  it('renders a back-to-inventory header on the install subview', () => {
+    mockPathname = '/settings/infrastructure/install';
+    renderWorkspace();
+
+    const backButton = screen.getByRole('button', { name: /Connections and Inventory/i });
+    expect(backButton).toBeInTheDocument();
+    expect(screen.getByText('Install on a host')).toBeInTheDocument();
+
+    fireEvent.click(backButton);
+    expect(navigateSpy).toHaveBeenCalledWith('/settings/infrastructure');
+  });
+
+  it('renders a back-to-inventory header on the platforms subview', () => {
+    mockPathname = '/settings/infrastructure/platforms/truenas';
+    renderWorkspace();
+
+    const backButton = screen.getByRole('button', { name: /Connections and Inventory/i });
+    expect(backButton).toBeInTheDocument();
+    expect(screen.getByText('Platform connections')).toBeInTheDocument();
+
+    fireEvent.click(backButton);
+    expect(navigateSpy).toHaveBeenCalledWith('/settings/infrastructure');
+  });
+
+  it('does not render the back-to-inventory header on the inventory landing', () => {
+    mockPathname = '/settings/infrastructure';
+    renderWorkspace();
+
+    expect(screen.queryByRole('button', { name: /^Connections and Inventory$/ })).toBeNull();
+  });
+
   it('hides the add-system action and redirects install routes in read-only mode', () => {
     presentationPolicyIsReadOnlyMock.mockReturnValue(true);
     mockPathname = '/settings/infrastructure/install';