fix(folio): stop spending the submit budget on taps the app refused

The window is an upper bound on the transactions an interval could hold, and
a bound inflated by taps that commit nothing is a bound the app can never
exceed: #78 read a rise of 15 transactions against 37 submits. TxnSubmit is
clickable(enabled = amount.isNotBlank()) and parseCents refuses anything its
regex misses, so a tap whose landing frame shows a refused amount cannot have
committed. Over four recorded android runs that is 19, 11, 25 and 25 of 35,
26, 42 and 42 submit taps.

A relaunch is excepted: a fresh process draws an empty field whatever was
submitted.

pkg/spec/test/folio-submit-window.test.ts

@@ -67,6 +67,96 @@ test("a second submit with no Home reading between them counts two", () => {
   );
 });
 
+// The window is a budget: an upper bound on the transactions the interval could
+// hold. A tap the app's own parser must have refused spends none of it, and on
+// android it does not even reach the parser, because TxnSubmit is
+// clickable(enabled = amount.isNotBlank()). Measured over four recorded android
+// runs, 19, 11, 25 and 25 of 35, 26, 42 and 42 submit taps landed on the
+// transaction screen with the amount field empty, so more than half the budget
+// was being spent on taps that cannot commit anything.
+test("a submit the app must have refused does not spend the window's budget", () => {
+  for (const amountText of ["", "   ", "0", "0.00", "00", "5.", "abc"]) {
+    assert.deepEqual(
+      countSubmitsInWindow({
+        previousCount: 0,
+        lastAction: { kind: "Tap", on: submitOn },
+        amountText,
+        fresh: false,
+      }),
+      { reported: 0, next: 0 },
+      `amount ${JSON.stringify(amountText)} was counted as a possible commit`,
+    );
+  }
+});
+
+// The field as the landing frame shows it, which is the form state the tap read:
+// nothing between the two changes it. Anywhere but the transaction screen there
+// is no field to read, and unknown has to count.
+test("an amount that could commit, or that nobody could read, spends the budget", () => {
+  for (const amountText of ["5", "0.01", "1,000", "999999999999999999999", undefined]) {
+    assert.deepEqual(
+      countSubmitsInWindow({
+        previousCount: 0,
+        lastAction: { kind: "Tap", on: submitOn },
+        amountText,
+        fresh: false,
+      }),
+      { reported: 1, next: 1 },
+      `amount ${JSON.stringify(amountText)} was dropped from the budget`,
+    );
+  }
+});
+
+// The one thing that can put a different form state on screen than the one the
+// tap read: the runner restarting the app, which the tap survives and the typed
+// amount does not. The field a fresh process draws is empty whatever was
+// submitted, so it proves nothing and the submit keeps its place in the budget.
+test("a submit across a relaunch spends the budget whatever the field shows", () => {
+  assert.deepEqual(
+    countSubmitsInWindow({
+      previousCount: 0,
+      lastAction: { kind: "Tap", on: submitOn, applied: true, relaunched: true },
+      amountText: "",
+      fresh: false,
+    }),
+    { reported: 1, next: 1 },
+  );
+});
+
+// What the budget costs the counting invariant, in the shape of the iOS run in
+// #78: a stretch of the walk that never went Home, most of it taps on a submit
+// button with nothing typed into the form, and one double tap that committed
+// twice. Counting the refused taps hands the app five transactions of slack it
+// never used, and two rows against six actions is no violation.
+test("refused submits used to hide a double submit behind their own budget", () => {
+  const frames = [
+    { amountText: "", lastAction: { kind: "Tap", on: submitOn } },
+    { amountText: "", lastAction: { kind: "Tap", on: submitOn } },
+    { amountText: "", lastAction: { kind: "Tap", on: submitOn } },
+    { amountText: "", lastAction: { kind: "Tap", on: submitOn } },
+    { amountText: "", lastAction: { kind: "Tap", on: submitOn } },
+    { amountText: undefined, lastAction: { kind: "DoubleTap", on: submitOn } },
+  ];
+  let budget = 0;
+  for (const frame of frames) {
+    budget = countSubmitsInWindow({
+      previousCount: budget,
+      lastAction: frame.lastAction,
+      amountText: frame.amountText,
+      fresh: false,
+    }).next;
+  }
+  assert.equal(budget, 1);
+  assert.equal(
+    committedTransactionsExceedSubmits({
+      countsBefore: { Checking: 3 },
+      countsAfter: { Checking: 5 },
+      submitsInWindow: budget,
+    }),
+    true,
+  );
+});
+
 // The two traces the freshness rule exists to tell apart, driven step by step
 // through the same pair of carriers the spec holds.
 function run(steps: { route: string | null; totalText?: string; lastAction: unknown }[]) {