feat(validations): merchant (bar/lavazh) ticket validations end-to-end

In-park merchants discharge customers' parking: a merchant user scans the
ticket on their device (/validate; validation:create + program↔user binding)
and applies their program — comp / first-N-minutes free / amount-off (capped,
typed at scan) / percent. All money stays at the booth: the quote folds live
validations in a canonical order (timeCredit → percent → fixed → comp, net
floors at 0, Σ lines ≡ gross − net), the payment records gross/discount and
CONSUMES the validation ids (an overstay's fresh period never re-applies
them), the receipt prints the gross → lines → net story, and the Z/X-report
carries discountTotalMinor leakage. Every apply/void is a signed, attributed
ledger event (refId = append-only void); program config is /setup/site master
data (Bar/Lavazh checkboxes + right-column panel, tabs when both) whose saves
sign config_change. Migration 0024 + reset-db drift-guard entries; 8 route
integration tests + priceSession fold suite.

See wiki/concepts/validation-discounts.md for the full design record.

Claude-Session: https://claude.ai/code/session_01YYkpEsLmoQPaize5ec3oUm

apps/server/src/pay-station.ts

@@ -1,9 +1,10 @@
 import { desc, eq, ledgerEvents, sessions, subscriptions, tariffVersions, tariffs, type Db } from "@parking/db";
-import { priceSession, type TariffStructure, type Tender } from "@parking/shared";
+import { priceSession, type TariffStructure, type Tender, type ValidationLine } from "@parking/shared";
 import type { FastifyBaseLogger } from "fastify";
 import type { EventLog } from "./event-log.js";
 import { plateForIdentity, platesForIdentities } from "./plate-lookup.js";
 import { windowOwedBetween } from "./subscription-window.js";
+import { liveValidations } from "./validations.js";
 
 // The PAY STATION: a customer pays for an open session BEFORE walking back to the
 // car (pay-on-foot — payment is decoupled from exit). Two steps:
@@ -38,8 +39,17 @@ export interface Quote {
    *  is priced as a fresh stay from there → now, with its own daily-cap ladder, NOT
    *  "full stay minus paid" (which a daily cap collapses toward zero). */
   readonly periodStart: string;
-  /** Amount owed now: the fee for [periodStart → now]. */
+  /** Amount owed now: the fee for [periodStart → now], NET of merchant validations. */
   readonly amountMinor: number;
+  /** The pre-validation fee (= amountMinor when no validations apply). */
+  readonly grossMinor: number;
+  /** Total the merchant validations took off (gross − net). */
+  readonly discountMinor: number;
+  /** Per-validation receipt/display lines (empty when none apply). */
+  readonly validationLines: ValidationLine[];
+  /** The validation event ids this quote applied — the payment stamps them as
+   *  CONSUMED so an overstay's fresh period never re-applies them. */
+  readonly validationIds: string[];
   /** True when this quote prices an overstay period (grace lapsed), not the first stay. */
   readonly overstay: boolean;
   readonly currency: string;
@@ -117,6 +127,12 @@ export interface SessionLookup {
   /** Advisory licence plate recognized for this session (ANPR-on-snapshot). Null when
    *  none. Display/audit only — never an access decision. */
   readonly plate: string | null;
+  /** Merchant validations folded into `amountMinor` (which is NET): the pre-discount
+   *  fee, the total taken off, and the per-validation lines for the modal/receipt.
+   *  grossMinor/discountMinor are null when no quote resolved. */
+  readonly grossMinor: number | null;
+  readonly discountMinor: number | null;
+  readonly validationLines: ValidationLine[];
 }
 
 export class PayStation {
@@ -155,19 +171,28 @@ export class PayStation {
     // Pure pricing shared with the Tariff Lab (priceSession). Only the latest payment
     // matters for grace/overstay; pass it through. Overstay → fresh period from
     // grace-expiry; within-grace → settled; unpaid → entry→now running total.
+    // Merchant validations: fold the LIVE ones (applied, unvoided, not consumed by a
+    // prior payment) so the quote is NET — the payment then stamps their ids as
+    // consumed. See wiki/concepts/validation-discounts.md.
     const last = this.#lastPayment(identity);
+    const validations = liveValidations(this.#db, identity);
     const p = priceSession(
       entry.occurredAt,
       new Date().toISOString(),
       structure,
       last ? [last] : [],
       category,
+      validations,
     );
     return {
       identity,
       enteredAt: entry.occurredAt,
       periodStart: p.periodStart,
       amountMinor: p.amountMinor,
+      grossMinor: p.grossMinor,
+      discountMinor: p.discountMinor,
+      validationLines: p.validationLines,
+      validationIds: validations.map((v) => v.eventId),
       overstay: p.overstay,
       currency: tv.currency,
       tariffVersionId: tv.id,
@@ -246,6 +271,18 @@ export class PayStation {
         // The exit flow reads graceExitMin off the payment to validate the
         // walk-back window without re-resolving the tariff.
         graceExitMin: q.graceExitMin,
+        // Merchant validations: record the gross/discount split + CONSUME the applied
+        // validation ids, so reporting sees the leakage and a later overstay period
+        // never re-applies them. A zero-net settlement (full comp) is still a signed
+        // payment — grace/voucher/exit work unchanged. See validation-discounts.md.
+        ...(q.validationIds.length
+          ? {
+              grossMinor: q.grossMinor,
+              discountMinor: q.discountMinor,
+              validationIds: q.validationIds,
+              validationLines: q.validationLines.map((l) => ({ ...l })),
+            }
+          : {}),
         ...(overrideMinor != null ? { reason: "operator-set amount", quotedMinor: q.amountMinor } : {}),
       },
     });
@@ -282,6 +319,7 @@ export class PayStation {
         paidAt: null, amountMinor: null, currency: null, paidMinor: null, paidCurrency: null,
         withinGrace: false, graceExpiresAt: null,
         overstay: false, subscription: false, subscriptionId: null, subscriptionHolder: null, plate: null,
+        grossMinor: null, discountMinor: null, validationLines: [],
       };
     }
     // Subscription occurrence? The entry payload carries permit:true + permitId.
@@ -319,11 +357,17 @@ export class PayStation {
     // exit gate clears. See wiki/entities/subscription.md.
     let amountMinor: number | null = null;
     let currency: string | null = null;
+    let grossMinor: number | null = null;
+    let discountMinor: number | null = null;
+    let validationLines: ValidationLine[] = [];
     if (open && !isSubscription) {
       try {
         const q = this.quote(id);
         amountMinor = q.amountMinor;
         currency = q.currency;
+        grossMinor = q.grossMinor;
+        discountMinor = q.discountMinor;
+        validationLines = q.validationLines;
       } catch {
         /* no active tariff — leave null; modal shows session without a price */
       }
@@ -344,6 +388,7 @@ export class PayStation {
       subscription: isSubscription, subscriptionId,
       subscriptionHolder: this.#holderOf(subscriptionId),
       plate: plateForIdentity(this.#db, id)?.plate ?? null,
+      grossMinor, discountMinor, validationLines,
     };
   }