When the user created a new board via the dashboard with "switch" checked,
the server-side `current` file was flipped to the new board. Clicking the
original board's tab then showed no cards even though the count badge read
correctly — the REST fetch dropped `?board=` when the selection was
"default" and the backend fell through to `current` (= the new board),
returning a different board's data than the tab the user clicked.
Fix:
- `withBoard()` always appends `?board=<slug>` when a board is selected,
including "default". The dashboard's tab selection becomes authoritative
instead of silently deferring to the server's `current` file.
- `writeSelectedBoard()` persists every selection (including "default")
to localStorage. Previously "default" was stripped, which meant the
next page load had nothing to pin to and fell through to `current`.
- Same change applied to the WebSocket query builder in `openWs()`.
Contract verified live:
current_board = "proj2"
GET /board → proj2's tasks (bug shape: falls through to current)
GET /board?board=default → default's tasks (fix: explicit pin wins)
GET /board?board=proj2 → proj2's tasks
Closes#20879.
b9f1ac8c10