diff --git a/.claude/skills/ssr-form-migration/reference/gotchas.md b/.claude/skills/ssr-form-migration/reference/gotchas.md
index 56846ae2..e0ccfdee 100644
--- a/.claude/skills/ssr-form-migration/reference/gotchas.md
+++ b/.claude/skills/ssr-form-migration/reference/gotchas.md
@@ -50,6 +50,39 @@ come from `GET /test-info`.
 
 ---
 
+## UI-only control fields must be stripped before a Datomic upsert
+
+The wizard snapshot/step-params carry UI control fields that are **not** schema
+attributes — `:action`, `:amount-mode`, and (added by the simple/advanced work) `:mode`.
+The `:manual` save handler stripped `:action`/`:amount-mode` but not `:mode`, so every
+*advanced* manual save passed `:mode "advanced"` into `:upsert-transaction` and 500'd with
+`:db.error/not-an-entity :mode`. Lesson: when a save derives its tx-data from the form
+snapshot, **strip every non-schema control key** before transacting. The session-backed
+wizard engine (Phase 6) avoids this class of bug by storing per-step *validated* data
+only — UI control fields never enter the combined data. This was a real production bug
+surfaced by the e2e gate, not a test artifact.
+
+## E2E helpers must use the Alpine **v3** API, not the v2 `__x` internal
+
+The app loads Alpine v3 (`cdn.jsdelivr.net/npm/alpinejs@3.x.x`). The v2 internal
+`el.__x.$data` is **gone** — `el.__x` is `undefined`, so any helper that pokes it silently
+no-ops. A stale `selectAccountFromTypeahead` did this and left the posted account empty
+(account-controlled by `x-model`, so the raw DOM `.value` you set is overwritten from
+Alpine's empty state). Drive components the real way instead: `window.Alpine.$data(el)`,
+open the tippy dropdown, inject `elements`, click the result — exactly as
+`transaction-edit-swap.spec.ts` does. Probe with
+`{ hasLegacy__x: !!el.__x, hasAlpineData: !!window.Alpine.$data(el) }`.
+
+## Diagnosing a "modal won't close after save"
+
+The edit modal closes on an `hx-trigger: modalclose` from a *successful* save; a
+validation failure re-renders the `#wizard-form` (200), and a server exception returns 500
+(caught by `wrap-error`). To find which: capture POST responses in Playwright
+(`page.on('response', …)`), read the `edit-submit` body — a `<form id="wizard-form">` means
+validation re-render; a `#error {…}` stack means a 500. Then serialize the form right
+before save (`new FormData(document.querySelector('#wizard-form'))`) to see exactly what
+posts. This is how the `:mode` 500 and the empty-account bugs above were isolated.
+
 ## Scorecard exceptions (ratchet violations with a reason)
 
 _None yet._ Append here if a migration must let a metric regress for a documented reason.
diff --git a/e2e/transaction-edit.spec.ts b/e2e/transaction-edit.spec.ts
index fc941d96..3f7d948e 100644
--- a/e2e/transaction-edit.spec.ts
+++ b/e2e/transaction-edit.spec.ts
@@ -41,68 +41,33 @@ async function getTestInfo(page: any) {
 }
 
 async function selectAccountFromTypeahead(page: any, rowIndex: number, accountName: string) {
-  // The account search uses Solr which isn't available in tests.
-  // Instead, we directly set the hidden input value via JavaScript.
-  
-  // Get all rows except the new-row, total, balance, and transaction total rows
-  const allRows = page.locator('#account-grid-body tbody tr');
-  const rowCount = await allRows.count();
-  
-  // Find the row that has a hidden input for account (actual account rows)
-  let accountRow = null;
-  let accountRowIndex = 0;
-  for (let i = 0; i < rowCount; i++) {
-    const row = allRows.nth(i);
-    const hasAccountInput = await row.locator('input[name*="transaction-account/account"]').count() > 0;
-    if (hasAccountInput) {
-      if (accountRowIndex === rowIndex) {
-        accountRow = row;
-        break;
-      }
-      accountRowIndex++;
-    }
-  }
-  
-  if (!accountRow) {
-    throw new Error(`Could not find account row at index ${rowIndex}`);
-  }
-  
-  // Find the hidden input for the account
-  const hiddenInput = accountRow.locator('input[type="hidden"][name*="transaction-account/account"]').first();
-  
-  // Get account IDs from test-info endpoint
-  const testInfo = await getTestInfo(page);
+  // Account search is backed by Solr (unavailable in tests). Drive the typeahead the
+  // way a user does, using the Alpine v3 API: open the tippy dropdown, inject a result
+  // into the component's `elements`, then click it. This runs the real click handler,
+  // Alpine reactivity and the HTMX swap exactly as in production -- unlike poking the
+  // long-removed Alpine v2 `__x` internal, which silently no-ops on Alpine v3 and left
+  // the posted account empty.
   const accountKey = accountName === 'Test' ? 'test-account' : 'second-account';
+  const label = `${accountName} Account`;
+  const testInfo = await getTestInfo(page);
   const accountId = testInfo.accounts[accountKey];
-  
   if (!accountId) {
     throw new Error(`Could not find account with name ${accountName}`);
   }
-  
-  // Set the hidden input value and trigger change
-  // Also update Alpine.js data to prevent it from overwriting our value
-  await hiddenInput.evaluate((el: HTMLInputElement, value: string) => {
-    // Set the DOM value
-    el.value = value;
-    
-    // Update Alpine.js component data
-    const alpineEl = el.closest('[x-data]');
-    if (alpineEl && (alpineEl as any).__x) {
-      (alpineEl as any).__x.$data.value.value = parseInt(value);
-      (alpineEl as any).__x.$data.value.label = 'Selected Account';
-    }
-    
-    // Also update any parent Alpine model (accountId)
-    const rowEl = el.closest('tr[x-data]');
-    if (rowEl && (rowEl as any).__x) {
-      (rowEl as any).__x.$data.accountId = parseInt(value);
-    }
-    
-    el.dispatchEvent(new Event('change', { bubbles: true }));
-  }, accountId.toString());
-  
-  // Wait for any HTMX updates
-  await page.waitForTimeout(300);
+
+  const row = page.locator('#account-grid-body tbody tr.account-row').nth(rowIndex);
+  const typeahead = row.locator('div.relative[x-data]').first();
+  await typeahead.locator('a[x-ref="input"]').click();
+  const search = page.locator('[data-tippy-root] input[x-model="search"]').first();
+  await search.waitFor({ state: 'visible' });
+  await search.fill('te');
+  await typeahead.evaluate((el: any, opt: { id: number; label: string }) => {
+    (window as any).Alpine.$data(el).elements = [{ value: opt.id, label: opt.label }];
+  }, { id: accountId, label });
+  await page.locator('[data-tippy-root] a', { hasText: label }).first().click();
+
+  // Wait for the change-gated whole-form swap to settle.
+  await page.waitForTimeout(400);
 }
 
 async function findAccountRow(page: any, rowIndex: number) {
diff --git a/src/clj/auto_ap/ssr/transaction/edit.clj b/src/clj/auto_ap/ssr/transaction/edit.clj
index 7b59ff84..1d264bd0 100644
--- a/src/clj/auto_ap/ssr/transaction/edit.clj
+++ b/src/clj/auto_ap/ssr/transaction/edit.clj
@@ -1235,7 +1235,10 @@
   [{:as request
     transaction :entity
     :keys [multi-form-state]}]
-  (let [tx-data (-> multi-form-state :snapshot (dissoc :action))
+  (let [;; :mode is a UI-only field (simple/advanced); :action/:amount-mode are control
+        ;; fields. None are Datomic attributes, so strip them before building the upsert
+        ;; (otherwise :upsert-transaction fails with :db.error/not-an-entity :mode).
+        tx-data (-> multi-form-state :snapshot (dissoc :action :mode))
         tx-id (:db/id tx-data)
         client-id (->db-id (:transaction/client tx-data))
         existing-tx (d-transactions/get-by-id tx-id)