[arsiihere]

Lane U3, task u8: 04 §4.5 row A-1, built against 01a v2.5 §6.18b (Script row and the "Day-close guard" note) and 01a tests #196 and #197. Marker: Cross (01a). Only the hub half: the client half (G-21) is task UA.

Spec sections

• 04 v1.0.2 §4.5 A-1.
• 01a v2.5 §6.18b (:1025, :1033), §9 DAY_CLOSE_BLOCKED (:1208), §10 tests 196 and 197 (:1498–1499).

Change (apps/hub/src/commands/close-business-day.ts)

• Exports DayCloseGuard = (db, state: Readonly<EngineState>) → { code: ErrorCode; details } | null, plus registerDayCloseGuard(fn), resetDayCloseGuard() and checkDayCloseGuard(db, state). This copies tables/merge-guard.ts: one guard, and a later registration replaces the earlier one.
• In handle, the guard is asked after the not_open and opened_recently returns and before withStockEffects / append. A non-null result throws new DomainError(code, details). The throw rolls the tx back, so there is no event and no processed_commands row. DAY_CLOSE_BLOCKED (409) already exists in @pos/domain (P0.3).

Tests added (apps/hub/test/commands/business-day.int.test.ts, describe "day-close guard"; afterEach now calls resetDayCloseGuard())

Test	Failing first
[01a #196] no guard registered → CloseBusinessDay closes as before, 0 extra statements	TypeError: registerDayCloseGuard is not a function
[01a #197] a stub guard → 409 DAY_CLOSE_BLOCKED with its details, no event, no processed_commands row, day still open; asked with (db, state) after not_open / opened_recently	TypeError: registerDayCloseGuard is not a function
[01a #197] a stub guard returning null → the day closes	TypeError: registerDayCloseGuard is not a function

(Before the implementation, the file's existing 11 tests also failed, on the resetDayCloseGuard import in afterEach.)

Run: business-day.int.test.ts → 14 passed. All 7 hub test files that send CloseBusinessDay → 106 passed. pnpm --filter @pos/hub typecheck and typecheck:tests are clean; eslint is clean.

Statement counts asserted (statementCounter, engine-host snapshot writes left out, as in the existing A-14 count test)

• With no guard, a guard that issues no statement and returns null gives the same count, and a guard doing one read gives +1. So the guard path costs only the guard's own reads, and unregistered costs 0.

Readings

• 01a v2.5 allows the guard "in close-business-day.ts (or a sibling day-close-guard.ts)". It is in close-business-day.ts, the row's file.
• The guard gets ctx.tx.db (the writer's connection, inside BEGIN IMMEDIATE) and ctx.state.

STOPs

None.

Needs: #94 (P0.3, DAY_CLOSE_BLOCKED), merged.

---

Generated by Claude Code