test: drive WaitTx's timeout and failed-lookup exits end to end (closes #315)

Two Chrome end-to-end cases send ETH and leave the wait for its receipt
running. In one, lookups answer "no receipt" until the 60-second deadline
ends the wait with the timeout message. In the other, a new fixture switch
makes every receipt lookup fail, and the sixth failure in a row ends the
wait with the message naming the unreachable network. Both check the exact
message and that Done returns to the address screen. Both wait in real
time: Playwright's clock would apply to every later test, and backdating
the stored broadcast time races the popup's own save.

Model: opus-5-5

tests/e2e/network.js

@@ -460,6 +460,16 @@ function rpcReply(req, opts, report) {
         return Object.assign(envelope, { result: ethCallResult(req, opts) });
     }
     if (req.method === "eth_getTransactionReceipt") {
+        // A lookup that fails, which the wait screen counts differently from
+        // one that answers "not mined yet" (README.md, WaitTx).
+        if (opts.failReceiptLookup) {
+            return Object.assign(envelope, {
+                error: {
+                    code: -32000,
+                    message: "e2e fixture: receipt lookup failed",
+                },
+            });
+        }
         const hash = Array.isArray(req.params) ? req.params[0] : null;
         return Object.assign(envelope, {
             result: opts.seedReceipt && hash ? transactionReceipt(hash) : null,
@@ -619,6 +629,8 @@ function traceEnabled(raw) {
  *   symbol is markup; read at request time.
  * @param {boolean} [opts.seedReceipt]  answer eth_getTransactionReceipt with a
  *   confirmed receipt instead of null, so a wait screen resolves.
+ * @param {boolean} [opts.failReceiptLookup]  answer eth_getTransactionReceipt
+ *   with an error, so every receipt lookup fails; read at request time.
  * @returns {Promise<{waitForServiceWorkerTraffic: (ms: number) =>
  *   Promise<string|null>}>}
  */