fix: a step the router lets fail is marked, and a balance check it lets fail sets no minimum (closes #602)

Each Universal Router release now carries the command types its dispatch()
can return a failure for instead of reverting, read from its source; only a
step of one of those with the allow-revert flag (0x80) set can fail while
the transaction goes on. Such a step is listed with "(allowed to fail)". A
BALANCE_CHECK_ERC20 the router lets fail guarantees nothing, so it is read
as a zero check and keeps an earlier step's minimum. Every swap and every
payment of ETH or an ERC-20 token succeeds or reverts the whole transaction,
so the flag on them has no effect and they read as without it.

Model: opus-5-5

tests/uniswap.test.js

@@ -987,13 +987,23 @@ describe("uniswap decoder", () => {
     );
 
     // A sub-plan holding a V3 swap of USDT for WETH, which the decoder does
-    // not read. With the allow-revert flag (0x80) the command byte is 0xa1.
+    // not read. With the allow-revert flag (0x80) the command byte is 0xa1,
+    // and the router lets the step fail
+    // (https://git.eeqj.de/sneak/AutistMask/issues/602).
     test.each([
-        { flag: "without", command: 0x21 },
-        { flag: "with", command: 0xa1 },
+        {
+            flag: "without",
+            command: 0x21,
+            steps: "Execute Sub-Plan (its steps are not shown)",
+        },
+        {
+            flag: "with",
+            command: 0xa1,
+            steps: "Execute Sub-Plan (its steps are not shown) (allowed to fail)",
+        },
     ])(
         "an EXECUTE_SUB_PLAN step $flag the allow-revert flag says its steps are not shown",
-        ({ command }) => {
+        ({ command, steps }) => {
             const subPlan = encodeSubPlan("0x00", [
                 encodeV3SwapExactIn(USER_ADDR, 2000000n, ONE_WETH, [
                     USDT_ADDR,
@@ -1013,9 +1023,7 @@ describe("uniswap decoder", () => {
                 USER_ADDR,
             );
             expect(result.name).toBe("Uniswap Swap");
-            expect(detail(result, "Steps").value).toBe(
-                "Execute Sub-Plan (its steps are not shown)",
-            );
+            expect(detail(result, "Steps").value).toBe(steps);
             // The sub-plan names both currencies, so the lines must not say
             // the calldata did not.
             expect(detail(result, "Token In").value).toBe(