docs(wiki): tariff research — legacy ParkSQL2017 schema, time-tiers & validation/sponsorship design

Ingest the predecessor SQL Server schema (raw + source summary) and file design
pages for time-of-day/seasonal tariff tiers and merchant validation/postpaid
sponsorship. Cross-link tariff.md and validation-discounts.md. No code.

wiki/concepts/validation-sponsorship.md

@@ -0,0 +1,94 @@
+---
+type: concept
+tags: [parking, domain, business, pricing, validation, design]
+sources: [parksql2017-legacy-schema]
+updated: 2026-06-17
+status: open
+---
+
+# Validation & Sponsorship — merchant comps, coupons, postpaid B2B
+
+Builds on [[validation-discounts]] (the signed-event discount mechanism) to add the layer it leaves
+open: **a sponsor account and postpaid B2B billing.** The driving case — **a nearby business with a
+postpaid agreement whose customers enter and exit freely, billed to the business monthly.**
+
+> This page owns the **sponsor/account/settlement** model and the **permit-vs-validation
+> distinction**. The *how a discount is applied* mechanics (signed event, `due = max(0, fee −
+> discounts)`, attribution, anti-abuse) live in [[validation-discounts]] — not duplicated here.
+> Status: **design, not built.**
+
+## Why this is NOT a permit (the key distinction)
+
+| | [[permit]] | Validation / sponsorship |
+| --- | --- | --- |
+| Subject | Known in advance; carries a credential (card/QR/plate) | Anonymous walk-in; identified only by the **ticket they were issued** |
+| When applied | At entry (credential opens the lane) | **After entry**, against an existing session — at a pay station, by a code, or by a sponsor rule |
+| Who pays | The subscriber, out-of-band | A **third party** (merchant/sponsor), or nobody (comp) |
+| Model fit | `permits` + credentials | New: a **validation event** on a session + a **sponsor account** |
+
+A permit bypasses tariff computation; a validation **adjusts the computed fee** (or zeroes it). They
+compose — but they are different primitives.
+
+## Two economic models (both real)
+
+- **Prepaid** — merchant buys a pool of value up front (legacy `BA_Cupons`: printed single-use codes
+  worth `DiscMinutes`; City Center research: merchant pre-buys time tickets 15 min→all-day).
+  Reconciliation = count used codes against the pool.
+- **Postpaid** (the asked-for case) — merchant signs an agreement; their customers park free or
+  discounted; the system **accrues each validation against a sponsor balance** and **invoices monthly**
+  (City Center: "billed for the number of tickets validated each month," verified 3-0). No money moves
+  at the lane.
+
+The legacy system did **only prepaid coupons** — **the postpaid sponsor account is net-new** for this
+project.
+
+## Modifier types (extends [[validation-discounts]])
+
+The discount-type enum lives in [[validation-discounts]]; legacy `DiscType` (smallint) and research
+(Amano McGann / HUB J4M, abstained-not-refuted) confirm the set: `comp` / `percent` / `fixed` /
+`time-credit` (legacy `DiscMinutes`) / `rate-switch`. **Sponsorship adds one field** to a validation:
+a `sponsorId`. Full-comp + a sponsor = the "free entry/exit, bill the business" case.
+
+## The sponsor-liability consequence (anti-fraud)
+
+The validation is a signed event ([[validation-discounts]], [[append-only-event-chain]]); what
+**sponsorship** adds is that **free-to-the-parker is not free-to-the-ledger** — it is a *receivable
+from the sponsor*. Under the [[threat-model|operator-as-adversary]] model:
+
+- A postpaid sponsor's "enter/exit freely" still **mints signed entry + exit events** (and snapshots)
+  — the audit trail is identical to a paying car; only the **settlement target** differs.
+- The **sponsor's period liability = the sum of `sponsorId`-tagged validation events** over the
+  period — derivable from the chain, reconcilable like a [[shift|shift Z-report]] and visible to
+  [[reconciliation]] (a sponsor comping far more than plausible footfall is an anomaly).
+
+## Proposed data shape (illustrative — design only)
+
+```
+sponsors          id, name, contact, mode {prepaid|postpaid},
+                  balance_minor (prepaid pool / postpaid accrual), billing_period, active
+validations       id, session_id, sponsor_id?, type, amount_minor|minutes,
+                  code?, operator_id, created_at   // append-only; one row per application
+(coupons)         code, value_minutes|minor, single_use, used_at?   // prepaid pool, optional
+```
+
+- A **postpaid** sponsor: each full-comp validation appends a row and accrues `amount` to the
+  sponsor; monthly invoice = sum over the period; exit is free at the lane.
+- **Free entry/exit "freely"**: either the sponsor issues credentials (then it's closer to a
+  [[permit]] — pick that path), or customers take a normal ticket and a sponsor rule / merchant code
+  comps it at exit. The agreement wording decides which; **both are expressible.**
+
+## Reconciliation & settlement
+- **Prepaid**: pool decrements; alert at low balance; no invoice.
+- **Postpaid**: accrue; **monthly statement** per sponsor (legacy/City Center cadence ~the 10th).
+  Statement lines trace to signed validation events → disputes resolvable against the chain.
+
+## Open
+- **"Enter/exit freely" mechanism**: sponsor-issued credentials ([[permit]]-like) vs. ticket +
+  comp-at-exit. Likely offer both; confirm the operator's actual deal shape.
+- Prepaid coupon format: printed codes (legacy) vs. QR vs. merchant web-validation portal.
+- Who may apply a validation, and the **per-operator cap** (a comp is a fraud vector — bound it and
+  always sign it).
+- Invoicing: in-app statement only, or export for external billing? FX if sponsor bills in another
+  currency (defer to [[tariff]] FX).
+- Partial-stay sponsorship (merchant covers first 2h, parker pays the rest) — `time-credit` or
+  `rate-switch` covers it; confirm.