fix: answer eth_chainId and net_version from loaded state (closes #317)

Both methods answered from the module-level state singleton, which the MV3
worker never populates, so a cold worker reported mainnet 0x1 to a page whose
user was on Sepolia.

They now answer from getState(), the per-call detached storage read the other
read handlers already use. An earlier revision of this fix used loadState()
instead and was rejected in review: it replaces the whole singleton, and these
methods are page-callable with no connection gate (inpage.js sends eth_chainId
on every page load), so a load landing inside backgroundRefresh()'s network
round trip detached the address objects being mutated in place — persisting
pre-refresh balances while still stamping lastBalanceRefresh, letting a polling
page suppress background refreshes indefinitely.

The test stub now structured-clones on get and set, as chrome.storage.local
does. The aliasing stub it replaces was independently measured to hide this
defect class entirely: with the aliasing get restored and the defective handler
in place, the suite passes 794/794.

Verified failing first three ways: a plain singleton read fails the three
cold-worker cases; the rejected loadState() revision fails only the new
mid-refresh case ("1.5" expected, "0" received); moving saveState() ahead of
refreshBalances() fails that case and only it.

src/background/index.js

@@ -3,7 +3,11 @@
 // non-sensitive calls to the configured Ethereum JSON-RPC endpoint.
 
 const { DEFAULT_RPC_URL } = require("../shared/constants");
-const { SUPPORTED_CHAIN_IDS, networkByChainId } = require("../shared/networks");
+const {
+    SUPPORTED_CHAIN_IDS,
+    networkById,
+    networkByChainId,
+} = require("../shared/networks");
 const { onChainSwitch } = require("../shared/chainSwitch");
 const {
     state,
@@ -663,12 +667,28 @@ async function handleRpc(method, params, origin) {
         return { result: [] };
     }
 
-    if (method === "eth_chainId") {
-        return { result: currentNetwork().chainId };
-    }
-
-    if (method === "net_version") {
-        return { result: currentNetwork().networkVersion };
+    // Both answered from currentNetwork(), which reads the module-level state
+    // singleton, and nothing populates that at module scope. A worker revived
+    // by the page's own message therefore held DEFAULT_STATE and told a page
+    // it was on mainnet while the user was on Sepolia
+    // (https://git.eeqj.de/sneak/AutistMask/issues/317).
+    //
+    // Answered from getState() rather than by loading the singleton. Any page
+    // reaches these two — neither is gated on a connection, and the injected
+    // provider sends eth_chainId on every page load — and loadState() replaces
+    // state.wallets wholesale, which would detach the address objects an
+    // in-flight backgroundRefresh() is mutating across its network round trip,
+    // so its saveState() would persist the pre-refresh balances while still
+    // stamping lastBalanceRefresh. getState() is the detached per-call storage
+    // read the other read handlers here already use.
+    // networkById(undefined) falls back to mainnet, matching the default for a
+    // profile with no stored networkId.
+    if (method === "eth_chainId" || method === "net_version") {
+        const s = await getState();
+        const net = networkById(s.networkId);
+        return {
+            result: method === "eth_chainId" ? net.chainId : net.networkVersion,
+        };
     }
 
     if (method === "wallet_switchEthereumChain") {