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.

src/popup/views/helpers.js

@@ -7,6 +7,7 @@ const {
     getAddressValueUsd,
 } = require("../../shared/prices");
 const { state, saveState, currentNetwork } = require("../../shared/state");
+const { markViewRendered } = require("../viewRouter");
 
 // When views are added, removed, or transitions between them change,
 // update the view-navigation documentation in README.md to match.
@@ -76,6 +77,10 @@ function showView(name) {
     }
     clearFlash();
     state.currentView = name;
+    // A view's show() ends here, so this is where the Back path learns the
+    // view is no longer the blank template from index.html and must not be
+    // rendered a second time. See viewRouter.js.
+    markViewRendered(name);
     saveState();
     updateDebugBanner(name);
 }
@@ -111,12 +116,19 @@ function updateDebugBanner(viewName) {
     }
 }
 
-// Callback to re-render the main/home view when navigating back to it.
-// Set once by index.js via setRenderMain().
-let _renderMain = null;
+// Callback that renders a view being navigated BACK onto. Set once by
+// index.js via setBackRenderer(), which routes the view through the same
+// per-view render and data guards restoreView() uses.
+//
+// It answers true when it took the navigation — the view is rendered and
+// shown, or its backing data was gone and it fell back — and false for a
+// view the popup does not render from persisted state. Those can only be
+// on the stack from this page load, because the stack is filtered on load,
+// so they have already been rendered and only need unhiding.
+let _renderBack = null;
 
-function setRenderMain(fn) {
-    _renderMain = fn;
+function setBackRenderer(fn) {
+    _renderBack = fn;
 }
 
 // Push the current view onto the navigation stack so goBack() can
@@ -136,9 +148,11 @@ function goBack() {
     } else {
         target = "main";
     }
-    if (target === "main" && _renderMain) {
-        _renderMain();
-    }
+    // A popped view is landed on, not navigated to. If the popup has been
+    // closed and reopened since the view was pushed, nothing has ever
+    // rendered it in this page load and its template is still blank, so it
+    // has to be rendered here rather than merely unhidden.
+    if (_renderBack && _renderBack(target)) return;
     showView(target);
 }
 
@@ -470,7 +484,7 @@ module.exports = {
     showView,
     onViewLeave,
     updateDebugBanner,
-    setRenderMain,
+    setBackRenderer,
     pushCurrentView,
     goBack,
     clearViewStack,