fix: Blockscout and Etherscan lookups are off until the user turns them on (closes #668)

Out of the box the wallet sent the user's addresses to Blockscout and each
recipient to Etherscan. Two settings, "Use Blockscout" and "Check recipients on
Etherscan", now gate those requests. Both are off in a new install and offered
unticked on Welcome and in Settings. While one is off, the screens that relied
on it say so in a plain line. Each gated request reads its setting from storage
before it asks and when the answer lands, and drops a late answer. An open popup
takes another page's change and draws its screens again. While "Use Blockscout"
is off, no address keeps an untracked token, and no screen names a token from
Blockscout's report. ENS lookups ask only the RPC endpoint.

Model: opus-5-5 (implementation); fable-5-1 (prose)

src/background/index.js

@@ -17,7 +17,11 @@ const { applyChainSwitchFields } = require("../shared/chainSwitchFields");
 // the same prohibition reported early, not the guarantee.
 const { getState, updateState } = require("./state");
 const { StateUnusableError } = require("../shared/stateSchema");
-const { refreshBalances, getProvider } = require("../shared/balances");
+const {
+    refreshBalances,
+    dropUntrackedTokens,
+    getProvider,
+} = require("../shared/balances");
 const { debugFetch, log } = require("../shared/log");
 const {
     verifySignedTx,
@@ -1386,6 +1390,10 @@ const RECENT_BALANCE_REFRESH_MS = Math.floor(BALANCE_REFRESH_PERIOD_MS / 2);
 // back over them (https://git.eeqj.de/sneak/AutistMask/issues/577).
 // lastBalanceRefresh is left as the switch set it, so the next tick refreshes
 // the new network.
+//
+// Blockscout may have answered just before the user turned "Use Blockscout"
+// off. So the save reads the stored setting again, and drops every token the
+// user has not tracked if the setting is off.
 async function backgroundRefresh() {
     const s = await getState();
     const now = Date.now();
@@ -1423,6 +1431,9 @@ async function backgroundRefresh() {
                 }
             }
         }
+        if (!fresh.useBlockscout) {
+            dropUntrackedTokens(fresh.wallets, fresh.trackedTokens);
+        }
         fresh.lastBalanceRefresh = now;
     });
 }