fix: render the view "Back" lands on after the popup is reopened (closes #268)

goBack() only unhid its target. A reopened popup renders the wallet list
and the one view restoreView() lands on, so every other view is still the
blank static template from index.html: pressing Back from Settings onto an
address showed an empty address line and no balances, and the same held for
address-token, receive, confirm-tx and transaction.

The per-view dispatch and its data guards move out of restoreView() into
src/popup/viewRouter.js, and goBack() now routes a popped view through the
same code by way of a renderer index.js registers with setBackRenderer().
A view whose backing state is gone falls back to Home the way the restore
does, rather than showing an empty template.

The Back path renders only a view this page load has not rendered yet.
viewRouter.js keeps a page-load-scoped set of rendered views, written by
showView() — the last thing every render path runs, forward navigation and
the restore alike, so a view added later registers itself rather than
needing to be remembered. Back onto a view already in that set unhides it
and nothing more, exactly as it does for a view outside RESTORABLE_VIEWS:
rendering a second time would re-fetch and overwrite what the view holds,
such as an edit typed into Settings and not yet saved. Home stays the
exception and is re-rendered on every Back, as it was when goBack() called
the renderWalletList() registered through setRenderMain(), so the wallet
list reflects what changed while the user was away from it.

tests/backNavigation.test.js drives the real goBack() over the reproduction
and over each of address-token, receive, confirm-tx, transaction, success-tx
and error-tx, with and without their backing state, and pins that a view
this page load already rendered — a live-session view, or Settings revisited
— is only unhidden, while Home still re-renders. tests/e2e/run.js adds three
cases against the real popup in a real browser, because make check cannot
see a blank view: a real close and reopen then Back onto the address screen
and onto Receive, and an in-session Back onto Settings that must keep
unsaved input. All three were demonstrated failing first.

TODO.md

@@ -45,6 +45,23 @@ undefined identifiers, which is how
 
 # Completed Steps
 
+- 2026-08-12: "Back" now renders the screen it lands on instead of only unhiding
+  it. A reopened popup renders the wallet list and the one screen it restores
+  onto, so every screen further down the stack was still the blank template from
+  `index.html`, and Back walked straight onto it — an empty address, no
+  balances, no QR code. The Back path now goes through the same per-view
+  dispatch and data guards as the restore (`src/popup/viewRouter.js`, shared
+  with `restoreView()`), falling back to Home when the state the target would
+  render is gone. It renders only a view this page load has not rendered yet:
+  `viewRouter.js` records every view that reaches `showView()`, which is where
+  forward navigation and the restore both end, so Back onto a view already on
+  the page unhides it and nothing more. That is what keeps a second render from
+  re-fetching and overwriting what the view holds — an unsaved edit in Settings,
+  a transaction list already loaded. Home is the exception and is always
+  re-rendered, as it was before. Covered by unit tests on the real `goBack()`
+  and by three end-to-end cases against the real popup, each demonstrated
+  failing on the unfixed build
+  ([#268](https://git.eeqj.de/sneak/AutistMask/issues/268)).
 - 2026-08-12: `KNOWN_SYMBOLS` now maps a symbol to the set of contract addresses
   that bear it, not to one of them. A ticker is not unique: seven of the 512
   bundled tokens — `FRAX`, `REUSD`, `TON`, `EURE`, `MSUSD`, `MUSD` and `JPYC` —