# Gotchas

GROWS every migration. One entry per surprise. Also the home for any **written exception**
to the scorecard ratchet (a metric that regressed for a documented reason).

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## Stale `$refs` / `tippy` after a swap

A whole-form swap can run an Alpine event handler *before* the component re-initialises,
so a handler that dereferences `$refs.input.__x_tippy` or calls `tippy.show()` throws.
**Always null-guard:** `$refs.input?.__x_tippy?.hide()`, `tippy?.show()`. The
`transaction-edit-swap.spec.ts` `trackErrors()` helper fails the test on any `pageerror`
or `console.error`, which is exactly how a stale-ref throw surfaces.

## Let the server value win — don't preserve Alpine state across a server-driven change

When a server change should update a component (e.g. choosing a vendor sets its default
account), rebuild that section fresh on the swap so the server-provided value lands
without keying tricks. The bug this prevents: "changing the vendor a *second* time doesn't
update the account" because preserved Alpine state shadowed the new server value. If you
*must* preserve a component, key it by value so a change forces re-init:
`(assoc attrs :key (str id "--" current-value))`.

## Focus dies if the typed input is inside its own swapped region

The single most important invariant. Amount field → swap a sibling tbody, not the row.
Memo → swap nothing. If a caret test (`sameNode`) fails, the input is in its own swap
region — re-target to a sibling/ancestor that excludes it.

## Faked cursors breed duplicate render fns

A `with-cursor`/`MapCursor` re-root to fake a deep start forces a `*-no-cursor*` twin.
Removing the fake lets you delete the twin. Don't "fix" a faked cursor in place — top-root
it and collapse to one render fn. (See `render-functions.md`.)

## Edit Clojure with clojure-mcp tools, not the file editor

`clojure_edit` / `clojure_edit_replace_sexp`. If a file won't compile: `clj-paren-repair`
the file, then retry; if still broken, `lein cljfmt check`. Run tests via `clojure-eval` /
`clj-nrepl-eval -p PORT`, never `lein test` (slow, last resort).

## Solr/typeahead in tests

Account/vendor search is backed by Solr, unavailable in tests. To drive a typeahead in
e2e: type under the 3-char threshold, then inject a result into Alpine state
(`Alpine.$data(el).elements = [{value, label}]`) and click it — the real click handler,
`tippy.hide()`, Alpine reactivity, and the HTMX swap all run as in production. Entity ids
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.
