harden: bound the total network fee by gasLimit × fee, on both send paths (closes #399)

The two per-field ceilings in approvalVerify.js were checked independently,
but the fee a validator is paid is gasLimit × fee per gas: a gas limit and a
fee each under their own ceiling still multiply to thousands of ETH, which a
gas-consuming contract really collects. assertWithinCeilings now also bounds
that product against MAX_TOTAL_FEE (1 ETH), so both callers — populating the
dApp transaction and verifying the signed artifact — refuse it with a full
sentence naming the fee and the limit.

The wallet's own send in confirmTx.js pinned no fee fields, so ethers filled
them from the node with no bound; it now populates the transaction and runs the
same check before signing, showing the same error in the confirmation screen's
reserved errors box so nothing on screen moves.

Model: opus-4-8

src/shared/approvalVerify.js

@@ -51,6 +51,7 @@
 const {
     Transaction,
     accessListify,
+    formatEther,
     getAddress,
     getBytes,
     verifyMessage,
@@ -134,10 +135,19 @@ const FORBIDDEN_FIELDS = [
 const MAX_GAS_LIMIT = 100000000n;
 
 // 100,000 gwei per gas: orders of magnitude above the highest fee either
-// supported network has produced, and low enough to catch a fee that would
-// hand the validator the balance.
+// supported network has produced.
 const MAX_FEE_PER_GAS = 100000000000000n;
 
+// The largest total fee this wallet will sign, in wei. The two ceilings above
+// bound the gas limit and the price per gas each on its own, but the fee a
+// validator is actually paid is their product, and a gas limit and a price
+// that are each under their own ceiling still multiply to thousands of ETH —
+// 30,000,000 gas at 100,000 gwei is about 3,000 ETH. Bounding the product is
+// what catches a fee that would hand the validator the balance; the per-field
+// ceilings alone do not. A full 30,000,000-gas block at 33 gwei reaches this,
+// which no ordinary wallet transaction approaches.
+const MAX_TOTAL_FEE = 1000000000000000000n; // 1 ETH
+
 // A refusal to act on an artifact: it is not the thing that was approved, so
 // the approval it was offered against is spent and must not be retried. Every
 // throw in this module is one of these; the background distinguishes them from
@@ -384,6 +394,28 @@ function assertWithinCeilings(tx) {
             );
         }
     }
+    // The product: gasLimit × the most this transaction could pay per gas —
+    // maxFeePerGas for a type-2 transaction, gasPrice for a legacy or type-1
+    // one. This is the fee a gas-consuming contract can really extract, and it
+    // is the bound the two per-field ceilings above cannot express.
+    if (present(tx.gasLimit)) {
+        const gasLimit = normalizeQuantity(tx.gasLimit, "gas limit");
+        let price = null;
+        if (present(tx.maxFeePerGas)) {
+            price = normalizeQuantity(tx.maxFeePerGas, "maximum fee per gas");
+        } else if (present(tx.gasPrice)) {
+            price = normalizeQuantity(tx.gasPrice, "gas price");
+        }
+        if (price !== null && gasLimit * price > MAX_TOTAL_FEE) {
+            throw refuse(
+                "This transaction would allow a network fee of up to " +
+                    formatEther(gasLimit * price) +
+                    " ETH, which is more than the " +
+                    formatEther(MAX_TOTAL_FEE) +
+                    " ETH this wallet will sign for.",
+            );
+        }
+    }
 }
 
 // Refuse a field only a transaction type this wallet does not sign can carry.
@@ -775,4 +807,5 @@ module.exports = {
     TX_STAGE_NONCE,
     MAX_GAS_LIMIT,
     MAX_FEE_PER_GAS,
+    MAX_TOTAL_FEE,
 };