Make swaps precise: drop no-op requests, swap only the affected field

Refine per-trigger granularity now that the swap target is explicit:

- Memo issues no request at all -- it affects nothing else, so its value just
  rides along in the form and is merged into the snapshot on save. (Changing the
  Location *value* likewise issues no request -- it never did; that cell's request
  is the account->location dependency.)
- Account select swaps only that row's Location cell (#account-location-<index> /
  #simple-account-location) instead of the whole form. Selecting an account only
  affects the valid Location options (computed from the posted account-id), so a
  precise cell swap is safe -- no snapshot dependency.

Account-structural changes (vendor, add/remove row, mode toggle, $/% radio) keep
swapping the whole form: their accounts+amount-mode state is interdependent and
round-trips through the single form-level snapshot hidden field, so a whole-form
swap is what keeps it consistent with zero OOB.

Update the memo test to assert it fires no request and keeps its value/caret.
Full e2e suite: 27 passed / 2 failed (same pre-existing, unrelated failures).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

e2e/transaction-edit-swap.spec.ts

@@ -179,9 +179,16 @@ test.describe('Transaction Edit whole-form swap', () => {
     expect(errors, errors.join('\n')).toEqual([]);
   });
 
-  test('preserves caret position in the memo text field across a swap', async ({ page }) => {
+  test('memo edits issue no request and keep their value/caret', async ({ page }) => {
     const errors = trackErrors(page);
 
+    // Memo affects nothing else in the form, so editing it must NOT issue a
+    // request at all -- its value just rides along in the form until save.
+    let memoRequests = 0;
+    page.on('request', (r: any) => {
+      if (r.url().includes('edit-form-changed') && r.method() === 'POST') memoRequests++;
+    });
+
     await page.goto('/transaction2');
     await page.waitForSelector('table tbody tr');
     await page.locator('button[hx-get*="/transaction2/"][hx-get*="/edit"]').nth(0).click();
@@ -190,22 +197,12 @@ test.describe('Transaction Edit whole-form swap', () => {
     const memo = page.locator('#edit-memo');
     await memo.waitFor();
 
-    // Clear any seeded memo text, then type "hello" via the keyboard (fires the
-    // field's htmx keyup trigger) and let that first post settle. Memo posts with
-    // hx-swap=none, so nothing is swapped back into the field.
+    // Clear any seeded memo text and type "hello".
     await memo.click();
     await memo.press('Control+a');
-    const firstSwap = page.waitForResponse(
-      (r: any) =>
-        r.url().includes('edit-form-changed') &&
-        r.request().method() === 'POST' &&
-        r.status() === 200
-    );
     await memo.pressSequentially('hello', { delay: 40 });
-    await firstSwap;
-    await page.waitForTimeout(300);
 
-    // Drop the caret in the middle (text inputs support selection).
+    // Drop the caret in the middle and insert a char -> "heXllo", caret -> 3.
     await memo.evaluate((el: HTMLInputElement) => {
       el.focus();
       el.setSelectionRange(2, 2);
@@ -213,17 +210,10 @@ test.describe('Transaction Edit whole-form swap', () => {
     await page.evaluate(() => {
       (window as any).__focusedMemo = document.activeElement;
     });
-
-    // Insert a char at the caret -> "heXllo", caret moves to 3, fires the post.
-    const memoSwap = page.waitForResponse(
-      (r: any) =>
-        r.url().includes('edit-form-changed') &&
-        r.request().method() === 'POST' &&
-        r.status() === 200
-    );
     await memo.press('X');
-    await memoSwap;
-    await page.waitForTimeout(300);
+
+    // Give the old debounce window a chance to (not) fire.
+    await page.waitForTimeout(500);
 
     const state = await page.evaluate(() => {
       const active = document.activeElement as HTMLInputElement;
@@ -235,6 +225,8 @@ test.describe('Transaction Edit whole-form swap', () => {
       };
     });
 
+    // No request fired, and the value/caret are simply intact (nothing swapped).
+    expect(memoRequests).toBe(0);
     expect(state.id).toBe('edit-memo');
     expect(state.sameNode).toBe(true);
     expect(state.value).toBe('heXllo');