fix(stalker): keep live playback when switching the ITV/radio category (#1517)

Switching the Live TV or radio category in the shell context panel tore
down the Stalker player: `onStalkerCategoryClicked` cleared the selected
item for every section, and the live layout gates its player on
`selectedItem`. Xtream live (#936) and M3U groups already keep the channel
playing across a category/group switch.

- Context panel: return before `clearSelectedItem()` for `itv`/`radio`;
  VOD/series clicks still drop the open detail before navigating.
- Live layout: the category-change reset effect no longer wipes the
  playing channel's short-EPG fallback or cancels a fallback load in
  flight; only a section change (itv <-> radio) does that now.
- Regression coverage in the context panel spec, the live layout spec and
  a new web E2E scenario; docs and a `.changes/` note added.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

docs/architecture/stalker-epg.md

@@ -310,6 +310,12 @@ therefore falls back to `get_short_epg` when:
 
 The fallback is merged with the bulk list rather than replacing it, so the
 panel shows "now" from the short EPG and the days ahead from the bulk guide.
+
+The fallback is keyed to the selected channel, not to the category: a category
+switch in the sidebar leaves the channel playing and keeps its fallback (and a
+fallback load still in flight) intact. It is dropped when the selection moves
+to another channel or when the view leaves ITV for radio, where the route
+session clears the selection.
 The stored fallback is tagged with the channel it was fetched for and the
 merge only applies while that channel is still selected — a channel switch
 moves the selection synchronously, while the old fallback is replaced only

docs/architecture/stalker-portal.md

@@ -1251,6 +1251,20 @@ The Stalker live route and radio route intentionally share
 - Some Stalker portals do not expose radio categories. Radio category loading
   falls back to a synthetic `PORTALS.ALL_RADIO` category with
   `category_id: '*'` so the station list can still be loaded.
+- A category click in the shell context panel only re-filters the channel
+  sidebar; the selected channel or station keeps playing (Xtream live #936 and
+  M3U group parity). `onStalkerCategoryClicked` therefore must NOT
+  `clearSelectedItem()` for `itv`/`radio` — the layout gates its player on
+  `selectedItem` — while VOD/series clicks still drop the open detail before
+  navigating to the list route. The layout's category-change reset effect
+  clears only list state (channels on the legacy paged flow, page, row EPG
+  previews); the active channel's short-EPG fallback and a fallback load still
+  in flight belong to the selection and survive the switch. Only a section
+  change (`itv` ↔ `radio`, where the route session clears the selection)
+  invalidates that request and drops the fallback. A playing channel outside
+  the newly selected category simply has no highlighted row, and remote
+  channel up/down finds no neighbour until a channel from the visible list is
+  played.
 
 ## Full ITV Channel List Cache
 

docs/architecture/workspace-shell.md

@@ -146,6 +146,14 @@ default. The panel header exposes a sort menu next to category search with
 synthetic "all categories" entries stay pinned before sorted provider
 categories.
 
+A category click in a LIVE section (Xtream `live`, Stalker `itv` and `radio`)
+changes only the selected category: the live layouts gate their player on the
+store's selected item, so the handler must not clear it — the channel the user
+is watching keeps playing while the sidebar re-filters (Xtream: #936; Stalker:
+`onStalkerCategoryClicked` returns before `clearSelectedItem()`). VOD and
+series category clicks do drop the open detail (`setSelectedItem(null)` /
+`clearSelectedItem()`) because they navigate to a list route.
+
 ## Search And Navigation Rules
 
 Search is shell-owned and route-aware: