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integreat/.claude/skills/ssr-form-migration/reference/gotchas.md
Bryce d0fad63e24 refactor(ssr): remove the EDN snapshot round-trip; transaction edit is a plain form (heuristic 2)
The wizard serialized the whole accumulating form state into a `snapshot` hidden field
(pr-str EDN + custom readers), decoded it every request, and merged step-params back in.
For this single-step modal the snapshot is pure redundancy: every value is either in the
entity or the live posted form. Remove it:

- render: EditWizard.render-wizard renders a plain form -- no snapshot / edit-path /
  current-step hidden fields; a single `db/id` hidden rides in the form instead.
- middleware: wrap-derive-state rebuilds :multi-form-state per request from the entity
  (loaded by the db/id hidden) overlaid with the live step-params, replacing
  wrap-init-multi-form-state + wrap-entity. The ~34 :snapshot reads are unchanged --
  :snapshot is now a derived map, not a round-tripped blob.
- editable fields (accounts, vendor, memo, approval, action, mode, amount-mode) come ONLY
  from the posted form (absent = cleared) so removing all account rows doesn't resurrect
  the entity's persisted accounts; only entity-only fields (db/id, client, amount, ...)
  come from the entity.
- delete the dead initial-edit-wizard-state and render-account-grid-body.
- e2e: make removeAllAccounts re-query each iteration (whole-form swaps stale a captured
  row index) and restore the percentage test to type-then-add ordering.

Scorecard: snapshot EDN round-trip + custom readers + merge-multi-form-state -> gone
(snapshot-field renders 0). Verified on a fresh server: full suite 38 pass / 1 unrelated
fail, swap 6/6, transaction-edit 8/8 -- same green as before, snapshot removed.
2026-06-03 15:20:26 -07:00

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# 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).
---
## 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.
## De-faking a cursor is not a drop-in — `with-field-default` mutates
Tempting fix for a faked deep cursor (`with-cursor` + synthetic `MapCursor` at index 0):
replace it with `(fc/with-field-default 0 {})` to advance naturally. **It broke the
simple-mode swap** (`transaction-edit-swap` test 1 threw). `with-field-default` calls
`cursor/transact!` — it *mutates the form cursor* (assoc-ing the default row) as a render
side effect, which changes simple-mode behavior. The read-only synthetic `MapCursor` did
not. Lesson: removing a faked cursor on these modals is **not** a one-liner — it's part of
the larger render-fn extraction (render the row from explicit data, construct field names
directly, look up errors explicitly), done when the simple/advanced rows are reworked into
pure render fns / Selmer. Don't swap one cursor primitive for another and assume parity;
verify against the swap spec, and expect the de-fake to come with the render-fn rewrite.
## Snapshot operations read stale state and drop live form values (heuristic 2)
The whole-form operation handlers (`apply-new-account`, `apply-remove-account`,
`apply-toggle-amount-mode`) rebuild the account rows from the **decoded `:snapshot`** (the
hidden EDN field), not from the live posted `:step-params`. So any value the user has typed
but that hasn't been re-serialised into the snapshot yet — e.g. an amount typed right
before clicking "New account" — is **silently lost** when the operation re-renders. This is
the snapshot round-trip fragility the migration removes (heuristic 2: → 0 merges; state
should ride in the form, not a parallel snapshot). It bit the percentage-split e2e: typing
50% then adding a row reverted the first row to its snapshot value, yielding a 66.67/33.33
split. Two ways it shows up and how to handle until the snapshot is gone:
**Fixed (Stage 1):** the operation handlers read the live `:step-params` rows (already
schema-decoded by `mm/wrap-wizard`) so typed values survive add/remove/toggle.
**Done (Stage 2 — the snapshot round-trip is gone).** The EDN `snapshot` hidden field +
custom readers + `merge-multi-form-state` are removed. A `db/id` hidden rides in the form;
`wrap-derive-state` rebuilds `:multi-form-state` per request from `entity step-params`,
and `EditWizard.render-wizard` renders a plain form (no snapshot/edit-path/current-step
hiddens). The ~34 `:snapshot` reads still work — `:snapshot` is now a derived map, not a
round-tripped blob.
**Trap that cost hours — derive `entity step-params` correctly.** First cut was
`(merge base step-params)`. Bug: `base` always carries the entity's *persisted* accounts,
so after the user removes every row (step-params has no accounts key) the merge falls back
to base → the persisted accounts **resurrect** on the next operation. Fix: editable fields
(accounts, vendor, memo, approval, action, mode, amount-mode) come **only** from the live
form (absent = cleared); only entity-only fields (`db/id`, client, amount, description,
status, type) come from the entity. Lesson: with a posted form, "field absent" means
*cleared*, not "use the persisted value" — never merge the entity's editable fields back in.
**Verify the snapshot removal on a FRESH server, and don't trust a long-lived in-process
test server.** Protocol/defrecord (`EditWizard.render-wizard`) and middleware reloads do
**not** fully take in a running REPL — the server kept rendering the old snapshot field
after `:reload`, and an in-process server that isn't reseeded between `npx playwright`
invocations accumulates state that makes order-dependent tests flake. Both produced hours
of phantom failures. Restart the REPL clean (or reseed) before trusting an e2e result; CI
boots a fresh server per run, so the fresh-server number (38 pass / 1 unrelated) is the real one.
## Characterization tests rot against table order and removed wizard chrome
Two stale-test traps surfaced once the masking failure was fixed (a `mode: 'serial'` file
hides every test after the first failure, so fixing one unmasks the next):
- **Hard-coded amounts per table row index** (`openEditModal(page, 3)` then
`expect(amount).toBeCloseTo(400)`) break because same-date seed transactions have no
pinned row order. Read the actual value (e.g. the grid's `.account-grand-total-row`)
instead of hard-coding.
- **Helpers that navigate the old multi-step wizard** (`click('button:has-text("Transaction
Actions")')`) hang once the modal is single-page. Drop the navigation; the action tabs
are present immediately.
## Scorecard exceptions (ratchet violations with a reason)
_None yet._ Append here if a migration must let a metric regress for a documented reason.