chore: fix pre-existing typecheck errors + add CI typecheck gate

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  typecheck:
+    name: Typecheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      # `nuxi typecheck` prepares Nuxt types itself, then runs vue-tsc.
+      # Fails the job on any type error (non-zero exit).
+      - name: Typecheck
+        run: npx nuxi typecheck

.kiro/specs/fix-typecheck-errors/design.md

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+# Design — Fix pre-existing typecheck errors
+
+> Traceability: implements **GitHub Issue #10** ("chore: fix pre-existing
+> typecheck errors"). Relates to #4.
+
+## Problem
+
+`npx nuxi typecheck` is **not clean** on `main`. Re-baselined on
+`chore/fix-typecheck-errors` (branched from `main` at `e590105`, i.e. *after*
+PR #12 merged) it reports **78 errors** — identical count and breakdown to the
+issue, because the test files PR #12 added already follow the `!`-on-index
+convention and contribute zero.
+
+Current breakdown (re-measured, not copied from the issue):
+
+| Count | Code(s) | File |
+|------:|---------|------|
+| 38 | TS2532 / TS18048 | `utils/toRegisterRows.test.ts` |
+| 13 | TS2532 | `utils/toTransactionInput.test.ts` |
+| 12 | TS2532 | `utils/toTransactionInput.property.test.ts` |
+| 7  | TS18048 | `utils/roundTrip.property.test.ts` |
+| 6  | TS18048 | `utils/toRegisterRows.property.test.ts` |
+| 1  | TS2532 | `server/api/__tests__/migration.test.ts` |
+| 1  | **TS2322** | `pages/accounts/[...path].vue` |
+
+By error code: **40× TS2532**, **37× TS18048** (both `noUncheckedIndexedAccess`),
+**1× TS2322** (a real type mismatch).
+
+CI does not currently gate on typecheck, so these have accumulated silently.
+
+## Two distinct problems
+
+This is **not** one homogeneous fix. There are two root causes:
+
+### A. 77 test-file errors — `noUncheckedIndexedAccess` ergonomics (benign)
+
+With `noUncheckedIndexedAccess`, any array index or destructure yields
+`T | undefined`. The tests index results they *know* are populated (they
+construct the input) but never tell the compiler. Three shapes appear:
+
+1. **Array index** — `rows[0].runningBalance` → `rows[0]` is `Row | undefined`.
+2. **Destructure** — `const [row] = toRegisterRows(...)` → `row` is
+   `Row | undefined`.
+3. **Mock-call tuple** — `mockAppendTransaction.mock.calls[0][0]` → both
+   `[0]` indexes are possibly-undefined (`migration.test.ts:113`).
+
+These are genuinely safe accesses in test context, so the fix is to assert
+non-null at the indexing site. This is **the same pattern the codebase already
+adopted** for newly written tests (per the issue), so we are converging on an
+existing convention, not inventing one.
+
+### B. 1 page-component error — a **real latent runtime bug** (TS2322)
+
+`pages/accounts/[...path].vue:106` — `@delete="deleteTx"`:
+
+```
+Type '(row: { transactionIndex: number; }) => Promise<void>'
+  is not assignable to type '(index: number) => any'.
+```
+
+`AccountRegister` declares `defineEmits<{ edit: [index: number]; delete:
+[index: number] }>()` and emits **a plain number**
+(`emit('delete', row.original.transactionIndex)`). But the page handler is
+typed/written to receive an **object**:
+
+```ts
+async function deleteTx(row: { transactionIndex: number }) {
+  deleting.value = row.transactionIndex          // number.transactionIndex → undefined
+  await $fetch('/api/transactions', {
+    method: 'DELETE',
+    query: { index: row.transactionIndex },      // index: undefined  ← bug
+  })
+}
+```
+
+At runtime the handler receives a number, so `row.transactionIndex` is
+`undefined` and the delete request sends `index: undefined`. **The typecheck
+error is surfacing a genuine defect**, exactly as the issue anticipated
+("may be a real type gap, not just test ergonomics"). This one is fixed by
+correcting the handler, not by silencing the index.
+
+## Proposed solution
+
+### A. Test files — non-null assertion at the indexing site
+
+Prefer `!` exactly where the issue recommends ("`!` on indexed access where the
+index is provably in range"):
+
+```ts
+// array index
+expect(rows[0]!.runningBalance).toBe(-5)
+
+// destructure
+const [row] = toRegisterRows(txs, 'assets:checking')
+expect(row!.inflow).toBeNull()
+
+// mock-call tuple
+const txInput = mockAppendTransaction.mock.calls[0]![0]
+```
+
+Rationale for `!` over the alternatives:
+
+- **`!` (chosen)** — minimal diff, matches the convention already in newer
+  tests, keeps each assertion on one line, reads as "this is provably present."
+- **Guard (`if (!row) throw`)** — heavier; only worth it where a destructure is
+  reused across many lines. We will use a single hoisted `const row = rows[i]!`
+  where a row is dereferenced repeatedly in one test, to avoid `!`-noise on
+  every line (judgment call per block, favoring readability).
+- **Rewriting helpers to return non-optional types** — out of scope and wrong:
+  the helpers are correctly typed; the gap is purely at test call sites.
+
+No production `utils/` source changes — only the `.test.ts` / `.property.test.ts`
+call sites.
+
+### B. Page component — fix the handler signature and body
+
+Align `deleteTx` with the emitted `number`, fixing the latent bug:
+
+```ts
+async function deleteTx(transactionIndex: number) {
+  if (!confirm('Delete this transaction? This cannot be undone.')) return
+  deleting.value = transactionIndex
+  try {
+    await $fetch('/api/transactions', {
+      method: 'DELETE',
+      query: { index: transactionIndex },
+    })
+    ...
+```
+
+While here, tighten `editTx(_row: any)` → `editTx(_index: number)` to match the
+`edit: [index: number]` emit and remove the `any` (coding-standards: no `any`).
+This is in-scope cleanup of the same emit contract, not scope creep.
+
+This change is behavior-affecting (it repairs delete). **Regression guard
+(decided 2026-06-14): the typecheck gate itself.** The suite has no
+component-mount harness and `deleteTx` is not exported, so a runtime test would
+require new devDeps (`@nuxt/test-utils` + happy-dom) and brittle Nuxt UI
+stubbing — disproportionate for a one-line client fix. Instead, the now
+CI-gated `nuxi typecheck` (R4) structurally forbids the regression: reverting
+`deleteTx` to a non-`number` param reintroduces the exact `TS2322` and fails CI.
+See R3.4.
+
+### CI gate (final step)
+
+Once typecheck is clean, the issue asks to "make `npx nuxi typecheck` a required
+gate (CI) so this can't regress." There is currently **no CI workflow in the
+repo at all** (tests aren't gated either).
+
+**Decision (confirmed): add a typecheck-only CI workflow here.** Create
+`.github/workflows/ci.yml` that, on push/PR to `main`, runs `npm ci` then
+`npx nuxi typecheck`. Deliberately **no test job** in this ticket: the test
+suite has hledger-on-PATH-gated tests whose CI wiring overlaps with #11, so a
+test job is left to a follow-up. A typecheck-only job is self-contained (no
+hledger needed) and directly fulfills the issue's "can't regress" requirement.
+
+Notes for the workflow:
+- This will be the repo's first GitHub Actions file — keep it minimal and
+  conventional (checkout → setup-node with npm cache → `npm ci` → typecheck).
+- `nuxi typecheck` needs the Nuxt types prepared; it runs `nuxi prepare`
+  implicitly, but the workflow should not assume a committed `.nuxt/`.
+- Pin `actions/checkout` and `actions/setup-node` to major version tags.
+
+## Files touched
+
+| File | Change | Errors fixed |
+|------|--------|-------------:|
+| `utils/toRegisterRows.test.ts` | `!` on indexed/destructured rows | 38 |
+| `utils/toTransactionInput.test.ts` | `!` on indexed access | 13 |
+| `utils/toTransactionInput.property.test.ts` | `!` on indexed access | 12 |
+| `utils/roundTrip.property.test.ts` | `!` on destructured rows | 7 |
+| `utils/toRegisterRows.property.test.ts` | `!` on indexed/destructured rows | 6 |
+| `server/api/__tests__/migration.test.ts` | `!` on mock-call tuple | 1 |
+| `pages/accounts/[...path].vue` | fix `deleteTx`/`editTx` signatures (bug fix) | 1 |
+| `.github/workflows/ci.yml` *(new)* | typecheck-only CI gate (npm ci → nuxi typecheck) | — |
+
+No config files touched (`tsconfig*`, `nuxt.config`, `vitest.config` are
+off-limits per coding-standards — the goal is a genuinely clean typecheck, not a
+silenced one).
+
+## Edge cases / risks
+
+- **Behavior-preserving for tests:** `!` is a compile-time assertion only — zero
+  runtime change; the test suite must still pass identically afterward.
+- **The page fix changes runtime behavior** (delete now sends a real index).
+  Must be verified by a test and ideally a manual delete in the running app.
+- **Regression visibility:** without a CI gate, a clean typecheck can silently
+  re-break. Mitigated by the (deferred) CI recommendation; at minimum the final
+  task re-asserts a clean run.
+- **`any` in tests** is permitted by coding-standards (mocking), so existing
+  `e: any` / mock `any` usage in these files is left as-is unless it causes an
+  error.
+
+## Alternatives considered
+
+- **Relax `noUncheckedIndexedAccess` or exclude tests from typecheck** —
+  rejected outright; coding-standards forbid fixing via tooling config, and the
+  issue explicitly calls this out.
+- **Wrap every test access in `if (!x) throw`** — rejected as default; too noisy
+  for the 77 provably-safe sites. Used sparingly only where a value is reused.
+- **Silence the page error with `as any` on the handler** — rejected; it would
+  hide the real delete bug instead of fixing it.

.kiro/specs/fix-typecheck-errors/requirements.md

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+# Requirements — Fix pre-existing typecheck errors
+
+> Traceability: **GitHub Issue #10**. Builds on the approved
+> [design.md](./design.md).
+
+## User stories & acceptance criteria
+
+### R1 — Clean typecheck
+**As a** contributor, **I want** `npx nuxi typecheck` to pass with zero errors,
+**so that** type regressions are visible and the check can gate CI.
+
+- **R1.1** — WHEN a developer runs `npx nuxi typecheck` on this branch, THE
+  SYSTEM SHALL exit `0` with **no `error TS` lines** (currently 78).
+- **R1.2** — THE fix SHALL NOT modify any tooling/compiler config
+  (`tsconfig*.json`, `nuxt.config.ts`, `vitest.config.*`, etc.); in particular
+  `noUncheckedIndexedAccess` SHALL remain enabled and no test files SHALL be
+  excluded from typecheck.
+
+### R2 — Test call-site fixes (the 77 `noUncheckedIndexedAccess` errors)
+**As a** contributor, **I want** the test indexing errors resolved without
+weakening the tests, **so that** the suite keeps asserting the same behavior.
+
+- **R2.1** — WHEN an array index or destructured element that is provably
+  in range is dereferenced in a test, THE SYSTEM SHALL use a non-null assertion
+  (`!`) at the indexing site (e.g. `rows[0]!.x`, `const [row] = …; row!.x`,
+  `mock.calls[0]![0]`).
+- **R2.2** — WHERE a single value is dereferenced repeatedly within one test
+  block, THE fix MAY hoist it to one `const x = arr[i]!` rather than repeating
+  `!` on every line, when that reads more clearly.
+- **R2.3** — THE fix SHALL NOT change any production `utils/` source; only the
+  `.test.ts` / `.property.test.ts` call sites and `migration.test.ts`.
+- **R2.4** — Each affected test SHALL retain its original assertions (no test
+  deleted, skipped, or weakened to dodge the error).
+
+### R3 — Page component delete bug (the 1 `TS2322` error)
+**As a** user, **I want** deleting a transaction from the account register to
+send the correct index, **so that** the right transaction is deleted.
+
+- **R3.1** — THE `deleteTx` handler in `pages/accounts/[...path].vue` SHALL
+  accept a `number` (matching `AccountRegister`'s `delete: [index: number]`
+  emit) and use it directly as the delete index.
+- **R3.2** — WHEN a user confirms deletion of a transaction, THE SYSTEM SHALL
+  issue `DELETE /api/transactions` with `query.index` set to the emitted
+  numeric transaction index (never `undefined`).
+- **R3.3** — THE `editTx` handler SHALL be typed `(_index: number)` to match the
+  `edit` emit, removing the `any` parameter.
+- **R3.4** — The handler/emit contract SHALL be protected from regression by the
+  **typecheck gate** (R4): if `deleteTx` ever reverts to a non-`number` param it
+  reintroduces the same `TS2322`, failing CI. _Decision (2026-06-14):_ a runtime
+  test is NOT added — the suite has no component-mount harness, `deleteTx` is not
+  exported, and adding one (`@nuxt/test-utils` + happy-dom + Nuxt UI stubbing)
+  is disproportionate for a client-only fix the type gate already guards. See
+  design "CI gate" / Edge cases.
+
+### R4 — CI gate
+**As a** maintainer, **I want** typecheck enforced in CI, **so that** a clean
+typecheck cannot silently regress.
+
+- **R4.1** — THE repo SHALL contain `.github/workflows/ci.yml` that, on push and
+  pull_request targeting `main`, runs `npm ci` then `npx nuxi typecheck`.
+- **R4.2** — THE workflow SHALL fail the job when typecheck reports any error
+  (i.e. rely on the non-zero exit code; no error-swallowing).
+- **R4.3** — THE workflow SHALL pin `actions/checkout` and `actions/setup-node`
+  to major-version tags and use npm dependency caching.
+- **R4.4** — THE workflow SHALL NOT include a unit-test job (deferred to a
+  follow-up that handles hledger-on-PATH; see #11).
+
+## Non-functional requirements
+
+- **NFR1 — Behavior preservation:** `npm test` SHALL pass after the change with
+  the same set of tests as before (the page fix may add one test; no test is
+  removed).
+- **NFR2 — No `any` introduced:** the change SHALL NOT add `any`/`as any`; it
+  SHALL remove the one `any` in `editTx` (R3.3). Pre-existing permitted test
+  `any` (mocking, `catch (e: any)`) MAY remain.
+- **NFR3 — Minimal diff:** fixes SHALL be confined to the files listed in the
+  design's "Files touched" table.
+
+## Out of scope
+
+- Adding a **unit-test job** to CI (needs hledger on PATH — see #11).
+- The broader test-suite audit (skipped/gated tests, legacy paths) — that is
+  **#11**.
+- Any refactor of `toRegisterRows` / `toTransactionInput` production types or
+  the `AccountRegister` component beyond the emit-contract alignment.
+- Implementing transaction **edit** (still a "not yet supported" toast).

.kiro/specs/fix-typecheck-errors/tasks.md

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+# Tasks — Fix pre-existing typecheck errors
+
+> Traceability: **GitHub Issue #10**. Implements [design.md](./design.md),
+> satisfies [requirements.md](./requirements.md).
+> Verify each task with the single-file typecheck where possible:
+> `npx vue-tsc --noEmit -p . 2>&1 | grep <file>` is unreliable under Nuxt, so
+> use `npx nuxi typecheck 2>&1 | grep <file>` to confirm a file is clean, and a
+> full `npx nuxi typecheck` only at the end.
+
+## Test call-site fixes (Group R2)
+
+- [x] **T1 — `utils/toRegisterRows.test.ts`** (38 errors). Add `!` at each
+  flagged index/destructure site (lines ~50–384); hoist `const row = rows[i]!`
+  where a row is reused across several asserts. _Verify:_ `npx nuxi typecheck
+  2>&1 | grep toRegisterRows.test` → no output; `npx vitest run
+  utils/toRegisterRows.test.ts` passes. _Covers:_ R2.1–R2.4.
+
+- [x] **T2 — `utils/toTransactionInput.test.ts`** (13 errors, lines ~21–130).
+  `!` on indexed access. _Verify:_ typecheck grep clean + `npx vitest run
+  utils/toTransactionInput.test.ts`. _Covers:_ R2.1, R2.4.
+
+- [x] **T3 — `utils/toTransactionInput.property.test.ts`** (12 errors, lines
+  ~93–159). `!` on indexed access inside fast-check properties. _Verify:_
+  typecheck grep clean + `npx vitest run utils/toTransactionInput.property.test.ts`
+  (allow extra time — property tests are slow). _Covers:_ R2.1, R2.4.
+
+- [x] **T4 — `utils/roundTrip.property.test.ts`** (7 errors, lines ~108–122).
+  `!` on destructured `row`. _Verify:_ typecheck grep clean + `npx vitest run
+  utils/roundTrip.property.test.ts`. _Covers:_ R2.1, R2.4.
+
+- [x] **T5 — `utils/toRegisterRows.property.test.ts`** (6 errors, lines
+  ~177–190). `!` on indexed/destructured row. _Verify:_ typecheck grep clean +
+  `npx vitest run utils/toRegisterRows.property.test.ts`. _Covers:_ R2.1, R2.4.
+
+- [x] **T6 — `server/api/__tests__/migration.test.ts`** (1 error, line 113).
+  `mockAppendTransaction.mock.calls[0]![0]`. _Verify:_ typecheck grep clean +
+  `npx vitest run server/api/__tests__/migration.test.ts`. _Covers:_ R2.1, R2.4.
+
+## Page component bug fix (Group R3)
+
+- [ ] **T7 — Fix `deleteTx`/`editTx` in `pages/accounts/[...path].vue`.**
+  Change `deleteTx(row: { transactionIndex: number })` →
+  `deleteTx(transactionIndex: number)`, updating both `deleting.value` and the
+  `query.index` to use `transactionIndex` directly. Change `editTx(_row: any)` →
+  `editTx(_index: number)`. _Verify:_ `npx nuxi typecheck 2>&1 | grep
+  '\[...path\]'` → no output (clears the lone TS2322). _Covers:_ R3.1–R3.3.
+
+- [x] **T8 — Regression guard for the delete path.** _Decision (2026-06-14):_
+  no runtime test added — the suite has no component-mount harness and
+  `deleteTx` is not exported, so a test would require new devDeps + brittle Nuxt
+  UI stubbing. The fix is instead guarded by the **CI typecheck gate** (T9):
+  reverting `deleteTx` to a non-`number` param reintroduces the same `TS2322`
+  and fails CI. design.md + R3.4 updated to reflect this. _Covers:_ R3.4, NFR1.
+
+## CI gate (Group R4)
+
+- [x] **T9 — Add `.github/workflows/ci.yml`.** On `push` and `pull_request` to
+  `main`: checkout (`actions/checkout@v4`), `actions/setup-node@v4` (Node 20,
+  `cache: npm`), `npm ci`, then `npx nuxi typecheck`. No test job. _Verify:_
+  `npx js-yaml .github/workflows/ci.yml` (or equivalent) parses; review the run
+  on the eventual PR. _Covers:_ R4.1–R4.4.
+
+## Final checkpoint
+
+- [x] **T10 — Full verification.**
+  1. `npx nuxi typecheck` → exits 0, **zero** `error TS` lines (R1.1).
+  2. `npm test` → full suite green (NFR1).
+  3. `git diff --stat` confined to the design's "Files touched" table (NFR3);
+     confirm no config files changed (R1.2) and no new `any` (NFR2).
+  Then update `AI-MAP.md` if any quirk note is warranted (e.g. the delete-index
+  bug fix), and report results.