fix(native): give the "Files" guide row its glyph

The guide renders `entry.icon`, and the `files` kind takeover registered
without one — so after the editor type stopped contributing its own
duplicate row (b56ceec), the single "Files" row was the only entry in the
new-tab list with a blank icon slot. The takeover now carries the editor
descriptor's icon (the takeover IS that descriptor's page).

Extracted `guideIconOf` so both registration sites build the icon field
the same way; the lifecycle test asserts the takeover's guide entry has
an icon.

src/client/native/index.ts

@@ -63,6 +63,17 @@ function titleOf(descriptor: TabDescriptor): string {
   return typeof descriptor.title === 'function' ? descriptor.title() : descriptor.title
 }
 
+/**
+ * The guide row's glyph for a descriptor icon (nothing when it has none).
+ * The native guide renders `entry.icon`, so a takeover registered without one
+ * is the only row in the list with a blank leading slot.
+ * @param icon - the descriptor's icon value.
+ * @returns the guide-entry icon fields, or an empty object.
+ */
+function guideIconOf(icon: TabDescriptor['icon']): { icon?: (props: { size?: number }) => unknown } {
+  return typeof icon === 'function' ? { icon: (props: { size?: number }) => icon(props.size ?? 16) } : {}
+}
+
 /**
  * The chip title of a file address: its own file name. A resource tab is
  * identified by its address, so the strip must name the FILE — the
@@ -171,9 +182,7 @@ export function registerNativeSurface(deps: NativeSurfaceDeps): () => void {
               order: descriptor.order ?? 100,
               title: () => titleOf(descriptor),
               description: () => t('nativeGuideDesc'),
-              ...(typeof icon === 'function'
-                ? { icon: (props: { size?: number }) => icon(props.size ?? 16) }
-                : {}),
+              ...guideIconOf(icon),
             }],
           }),
       })
@@ -189,7 +198,7 @@ export function registerNativeSurface(deps: NativeSurfaceDeps): () => void {
     }
 
     /** One `files`-kind takeover: the plugin's explorer under the built-in kind. */
-    const registerFilesKind = (): (() => void) => {
+    const registerFilesKind = (editor: TabDescriptor | undefined): (() => void) => {
       const id = 'dsh-better-sidebar:files'
       const disposeType = tabs.register({
         id,
@@ -200,6 +209,10 @@ export function registerNativeSurface(deps: NativeSurfaceDeps): () => void {
           order: 10,
           title: () => t('files'),
           description: () => t('nativeGuideDesc'),
+          // The takeover IS the editor descriptor's page, so it carries the
+          // editor's glyph: without it the "Files" row is the only guide
+          // entry with an empty icon slot.
+          ...guideIconOf(editor?.icon),
         }],
       })
       const slots = registerSlots(id, { ctx, store, service, records, descriptorId: EDITOR_KIND }, {})
@@ -229,7 +242,9 @@ export function registerNativeSurface(deps: NativeSurfaceDeps): () => void {
       // editor disabled the plugin has no explorer to put there.
       const wantsFiles = service.isTabEnabled(EDITOR_KIND)
       const hasFiles = live.has(FILES_KIND)
-      if (wantsFiles && !hasFiles) live.set(FILES_KIND, { dispose: registerFilesKind() })
+      if (wantsFiles && !hasFiles) {
+        live.set(FILES_KIND, { dispose: registerFilesKind(service.getTab(EDITOR_KIND)) })
+      }
       if (!wantsFiles && hasFiles) {
         live.get(FILES_KIND)?.dispose()
         live.delete(FILES_KIND)

tests/native-surface.spec.ts

@@ -88,7 +88,7 @@ describe('service routing into the native surface', () => {
     service.setSurface(surface)
     service.registerTab({ id: 'terminal', title: 'Terminal', component: () => null, createTab: state => ({ tab: { id: `terminal:${state.nextTerminal}`, type: 'terminal', title: 'Terminal', meta: { n: state.nextTerminal } } }) })
     service.registerTab({ id: 'git', title: 'Changes', component: () => null })
-    service.registerTab({ id: 'editor', title: 'Files', component: () => null })
+    service.registerTab({ id: 'editor', title: 'Files', component: () => null, icon: () => null })
     return { surface, calls, service }
   }
 
@@ -163,7 +163,7 @@ describe('registerNativeSurface lifecycle (service-driven registration)', () =>
     store.setSession('s1')
     const service = createBetterSidebarService(store)
     service.registerTab({ id: 'terminal', title: 'Terminal', component: () => null })
-    service.registerTab({ id: 'editor', title: 'Files', component: () => null })
+    service.registerTab({ id: 'editor', title: 'Files', component: () => null, icon: () => null })
     const records = createNativeTabRecords()
 
     const registered: Array<{ id: string; kind: string; title: (address: string) => string; guide: unknown }> = []
@@ -223,6 +223,10 @@ describe('registerNativeSurface lifecycle (service-driven registration)', () =>
     expect(editorType?.guide).toBeUndefined()
     const filesType = registered.find(entry => entry.kind === 'files')
     expect(filesType?.guide).toBeDefined()
+    // The takeover carries the editor's glyph, so the "Files" guide row is
+    // not the only one with a blank icon slot.
+    const filesGuide = filesType?.guide as Array<{ icon?: unknown }> | undefined
+    expect(filesGuide?.[0]?.icon).toBeDefined()
 
     dispose()
   })