scrabble-game/docs/PAYMENTS.md

# PAYMENTS — monetization mechanics

Authoritative specification of the monetization domain: the in-game currency, wallets,
benefits, store-compliance rules, payment intake, ads, catalog, ledger, and reporting.
English is authoritative; [`PAYMENTS_ru.md`](PAYMENTS_ru.md) mirrors it in plain Russian
(mirror every point edit in the same PR, like `FUNCTIONAL.md`/`FUNCTIONAL_ru.md`).

Read this before changing any payments behaviour. The technical implementation plan lives
in [`../PLAN.md`](../PLAN.md).

> Status: specification approved; implementation staged (see `PLAN.md`). Nothing here is
> live yet.

## 1. Overview

The game earns through two orthogonal channels:

- **Purchases** of the in-game currency **Фишка** (chips) with real money, then spending
  chips on **values** (benefits).
- **Ads** — a rewarded video tops chips up; an interstitial and a house banner monetize by
  impression.

The currency is **two-tier**:

```
money (VK Votes / TG Stars / RUB via Robokassa)  ─┐
                                                  ├─►  Фишки (chips)  ──►  values
rewarded ad view                                 ─┘                         (no-ads, hints,
                                                                             tournament fee)
```

Chips are the single storefront unit. Money and rewarded views **fund** chips; chips
**buy** values. There is no path that spends money directly on a value — always through
chips.

## 2. Currency model

**One chip is one chip everywhere** — the unit is uniform. The difference between payment
methods lives entirely in the **purchase rate**: a chip pack costs *X* Votes / *Y* Stars /
*Z* RUB, and the rate absorbs each store's commission. Value prices are fixed **in chips**
and identical across methods.

The chip balance is **segmented by `source`** — the platform where the chips were funded:

| `source`   | Funded by                        |
|------------|----------------------------------|
| `vk`       | VK Votes purchase, VK rewarded ad |
| `telegram` | TG Stars purchase                |
| `direct`   | Robokassa purchase (web / native)|

A single account holds all three segments simultaneously: `balance = (account_id, source)`,
up to three rows — a row is materialised lazily on the segment's first funding, and an absent
segment reads as zero. Segmentation is **not** per-identity — see §6.

Why segmented, not one pooled balance: store rules forbid activating value that was paid
for outside the store's own cash desk. Chips funded inside VK (Votes) may only be spent in
the VK context; Stars only inside Telegram; Robokassa-funded (`direct`) chips only outside
the stores. See §4.

## 3. Three operations, kept distinct

Do not conflate these — they use different keys:

1. **Fund chips** — money/ad → chip `source` segment, keyed by the **execution context**.
2. **Spend chips = buy a value** — segment → benefit, keyed by context with the gate (§4).
   This is where a benefit is **born** and stamped with its `origin`.
3. **Apply a benefit** over time (e.g. "no-ads until *T*") — governed by the origin rule
   (§5).

`source` (where chips were funded) and `origin` (where a value was bought) share the same
value set `{vk, telegram, direct}` but mean different things. On the web they can diverge:
web spending may draw `vk` chips (`source=vk`) into a `direct` purchase (`origin=direct`).

## 4. Store-compliance gate

The compliance wall is **one-directional**. The dangerous direction — activating externally
paid value *inside* a store wrapper — is blocked; the safe direction (a store benefit
leaking out to the open web) is allowed.

**Spend context → which segments/benefits are usable:**

| Execution context   | Spendable chip segments | Spend priority     |
|---------------------|-------------------------|--------------------|
| Inside VK (Android) | `vk`                    | —                  |
| Inside VK (iOS)     | none — frozen (view only)| —                 |
| Inside Telegram     | `telegram`              | —                  |
| Web / native (Direct)| `direct` + `vk` + `telegram` | direct → vk → tg |

- Inside VK/TG only the same-named segment is usable; everything else (chiefly `direct`) is
  invisible-as-spendable there.
- On the web the store has no jurisdiction, so all attached segments are spendable, drained
  by priority direct → vk → tg.
- **VK iOS** is frozen for spending (Apple forbids spending virtual currency on digital
  goods outside IAP inside VK on iOS): the balance is shown as a number, but no purchase or
  spend is possible. A previously bought benefit still *applies* there.

The account is **single** (identities merge, one profile/friends/stats). The gate is
**logical**: in a VK/TG context the server activates only the same-named segment. It rests
on a **trusted platform signal** (§8) — the client is never believed. When the platform
cannot be trusted, the gate is **fail-closed**: spends/purchases are denied, view only.

### One-directional benefit application

A benefit carries `origin` = the **purchase context** (not "what it was paid with"). Buying
on the web with `vk` chips still yields `origin=direct`.

| `origin`         | Where the benefit applies                          |
|------------------|----------------------------------------------------|
| `vk` / `telegram`| **Everywhere** — inside its store *and* out on web/native |
| `direct`         | **Only** web/native — never inside VK/TG (= store ban) |

Before a web spend draws `vk`/`telegram` chips, the UI **warns** the user that the value
will be available here (web/native) only, because of VK/TG restrictions.

## 5. Benefits

Three distinct entities, do not merge:

- **Chips** — currency. Segment by `source`.
- **Hints** — consumable, bought with chips. Segment by `origin`. Spent one-per-hint in
  online games; `vs_ai` hints stay free/unlimited (30-min idle gate, not counted). A hint
  spent in a game is drawn from an `origin` applicable to the current context (same
  one-directional relaxation as above).
- **No-ads** — a duration benefit, bought with chips. Segment by `origin`.

**No-ads stacking.** Buying a term extends `paid_until[origin] += term` from
`max(now, current end)` — the remainder is never lost ("terms add up"). **Forever** is a
separate perpetual flag that overrides terms. "Ads off in context *P*" ⇔ some `origin`
applicable in *P* has `paid_until > now` (on the web take the max over direct/vk/tg; in VK
only vk; in TG only tg).

**What no-ads suppresses:** the top banner **and** the post-move fullscreen interstitial.
The voluntary **rewarded** view (for chips) is never suppressed — it is the user's choice.

**Tournament fee** — a future value type; the atom is provisioned but the mechanic ships
later.

## 6. Wallet lifecycle

**Segment availability rule.** A segment is spendable ⇔ the account has an identity of that
`source` (for `direct`: a durable identity/email). This makes unlink/merge fall out
naturally.

**Unlink (vk/tg).** Allowed even with a non-zero balance/active benefit. The segment is not
burned — it **sleeps** (no identity ⇒ unavailable in VK *and*, lacking the attachment,
unavailable as an attached web segment); re-linking wakes it. The user is warned before
unlinking ("N chips will be unavailable until you re-link"). The last identity cannot be
unlinked (existing `ErrLastIdentity`).

**Merge.** Segments and benefits merge **by origin**: same-origin segments add (chips sum,
benefit terms extend per origin), different origins coexist. This extends the current
account-merge (`hint_balance +=`, `paid_account OR=`) so origin is preserved and nothing
leaks across platforms.

**Guest.** A guest account has **no wallet at all** — the Wallet section is hidden, no
purchases, no balance, by design. Balances belong only to durable accounts. The guest
reaper therefore deletes guests freely (no money can exist there). In `direct`, email is
required **before the first purchase** as a recovery anchor (in VK/TG the vk/tg identity is
already the anchor); the existing email flow (request code → confirm → clear guest →
durable) is reused.

## 7. Catalog and pricing

The catalog is **configurable** — products, prices, purchase rates, and rewarded payout
live in the database and are edited in the admin console, no release required.

- **Base values (atoms):** chips, hints, no-ads days, tournament entry.
- **Product = a set of atoms + a price.** Sold singly or as a combo (e.g. "250 hints + 30
  no-ads days").
- **Chip pack** (funds chips) — priced **per method** (multi-currency Votes/Stars/RUB) as a
  single product.
- **Value** (bought with chips) — priced **in chips** (uniform across methods).

**Deactivation, not deletion.** Products are soft-deleted (deactivated). A completed
purchase stores a **snapshot** of what was sold (atom composition + price at the time) into
an archive, so history/receipts/tax are independent of later catalog edits.

## 8. Trusted platform signal

The gate (§4) needs a **trusted, unforgeable** platform context on the server. The client is
never the source of truth.

- The platform is a **property of the session**, captured when the session is created. VK and
  Telegram wrappers re-mint (and so re-validate the launch signature — VK launch-params `sign`
  / Telegram `initData`) on **every cold start**, so their platform is re-confirmed each launch;
  a `direct` session captures it once, established by the fact of a web/native session's creation
  (no external signer, and none needed — reaching vk/tg segments in a direct context still
  requires a real attachment, §6).
- The platform carries **kind** (`vk`/`telegram`/`direct`) **plus subtype**
  (`ios`/`android`/`web`). `kind` is always trusted — the server derives it from the validated
  launch, never a client field. The **subtype is trusted only for VK**: it rides inside the
  signed launch parameters, which is what makes the **VK iOS freeze** enforceable; for Telegram
  and direct the subtype is client-reported and best-effort, so the gate never keys off it.
- The gateway resolves the session and passes `platform` to the backend (alongside the existing
  `X-User-ID`), sourced from the session — never the client request body.
- **Fail-closed:** an untrusted platform — a session with no recorded platform, one predating
  this feature or one the gateway could not attribute — denies spends/purchases and applying any
  foreign origin (view only). A VK/TG session recovers on its next cold-start re-mint; a reused
  direct/email session on re-login.

## 9. Payment intake

**Server callback only.** Chips are credited solely on a **verified** (signature/HMAC)
provider callback — Robokassa webhook / TG `successful_payment` / VK callback. A client "I
paid" is ignored.

**Single writer.** One payments domain is the only writer of the ledger. Public webhooks
(Robokassa/VK) terminate at the edge (Caddy/gateway) and proxy into payments; TG
`successful_payment` reaches the bot, which forwards into payments. One place credits and
dedupes.

**Order-flow.** The server pre-creates an `order(pending)` with account / platform / pack /
expected amount / origin. The `order_id` is threaded to the provider (Robokassa `InvId` / TG
`invoice_payload` / VK `item` — confirm the exact VK field at integration). The callback
matches by `order_id` (never by amount, so equal-amount collisions cannot happen), verifies
the amount, credits, marks `paid`. **Idempotency:** dedup by `(provider, provider_payment_id)`.

**Pending is invisible** to the user; it auto-expires on a timeout (~30 min, DB hygiene). A
valid callback is **always** honoured, even on an expired order (`expired` ≠ cancellation —
the money is real, the chips are owed). The user sees only successful purchases.

**TG Stars.** Only the **bot** reaches Telegram, so the whole rail funnels through the reverse
mTLS **bot-link** (bot ↔ gateway; the bot cannot dial the backend). The invoice is minted by the
bot: on the order path the gateway sends a `CreateInvoice` command and the bot returns a
`createInvoiceLink` (XTR) in its Ack, which the Mini App opens with `WebApp.openInvoice`. Before any
star moves the bot answers `pre_checkout_query` via a bot→gateway `ValidatePreCheckout` unary
(backed by the intake): approve only if the order exists, is still creditable and is **not already
paid** — a Stars invoice link is reusable, so this gate is the one place a repeat payment is stopped
before the charge; the decline reason is localised to the order account's language.

`successful_payment` reaches the bot only (Bot API, not the Mini App), and the bot host is weak and
can lose connectivity, so the bot is a durable link. Store-and-forward on **SQLite** on the bot's
disk (`internal/outbox`): persist on receipt (idempotent on `telegram_payment_charge_id`) → forward
over the bot-link (a `ForwardPayment` unary; the gateway proxies to the intake) → on a durable
response, mark `forwarded`. Re-drives undelivered on restart and on a periodic tick. At-least-once
delivery + idempotent intake (dedup by `telegram_payment_charge_id`) = credited exactly once.

**Events.** The payments domain writes `payment_events` (succeeded / failed / refunded); a
dispatcher fans out over channels — the live gRPC stream if the user is in-app, else the
existing `botlink` push / email relay. "Payment failed" (an **active** provider decline, not
an abandoned pending) is surfaced to the user; "payment succeeded" is a hook (email / bot
message).

**Refunds.** ToS is **non-refundable** — we do not offer refunds to the user. An admin may
issue a **manual** refund (edge case: a user demands one shortly after paying / closes their
account — tie into `accountdelete`, which already preserves messages). **External** refunds
(chargeback / store decision / TG / VK) are honoured: the system takes the `refunded` event,
**best-effort** revokes the benefit (never going negative; if chips were already spent, it
records the loss + an abuse flag), and writes to the ledger. The ledger is **export-ready**
for future tax reporting and Robokassa reconciliation (reconciliation itself is not built
yet; the schema stays compatible).

## 10. Ads

**Launch scope: VK only** for video (rewarded payout in RUB, ОРД automatic, API ready).
web/native/TG keep the existing house **text banner** only; video is deferred until a
ruble-paying in-app network exists. The ad provider is behind an **abstraction** so a future
network for other platforms slots in without rework. Crypto-payout networks (AdsGram/AdMob)
are rejected — no legal ruble income for a self-employed (НПД) developer.

**Rewarded** (voluntary video for chips) credits chips through payments on the network's
**server verify callback** (client not believed, like a payment). On-launch anti-fraud is
the provider's verify only (no own daily cap yet; the abstraction allows adding caps later).

**Interstitial** (post-move fullscreen), configurable server-side values:

- Global cooldown **per user, across all games**, default **5 min**.
- **`vs_ai` — 30 min** (aligned with the hint cooldown, so it does not scare casual players).
- Applying a **hint** triggers a post-move interstitial **independently** of the main
  cooldown, with its own **1-min** cooldown.
- Offline — banner only.
- Respect VK's own frequency caps.

**No ads offline** beyond the house banner. The `no-ads` benefit suppresses the banner via
the existing `ads.Eligible` (`backend/internal/ads/ads.go`), which is extended to gate on
the **origin benefit applicable in the current context** rather than one global flag.

## 11. Admin, audit, reporting

**Append-only ledger + materialized balance.** The operations ledger is **INSERT-only**
(never UPDATE/DELETE — full audit). Segment balances `(account, source)` and benefits
`(account, origin)` are a fast **materialized** cache, updated **in the same transaction** as
the ledger write, and recomputable from the ledger for reconciliation.

**In-process read cache.** On top of the materialized tables, the payments package keeps an
in-process, account-keyed, write-through cache of each account's segments and benefits, so the
hot read paths — the ad-eligibility check, hint availability, the wallet view, the spend gate
— issue **no** query to the `payments` schema on the steady-state path. It is invalidated on
every payments mutation (spend / grant / fund / refund / merge) and re-read from the
materialized tables on a miss (the same write-through pattern the account-suspension gate
uses). Single-instance, matching the deployment; a multi-instance backend would need a shared
cache. Identity-presence (which segments are awake, §6) is supplied by the caller, not cached
here, so unlink/re-link takes effect immediately.

**Admin rewards.** An admin grants **concrete values only** (no-ads / hints) — **never
chips** (a gifted currency balance = a store cash-desk bypass). The admin **picks the
origin** at grant time (compliance is on them: `origin=vk` point-wise/low-volume = low risk,
`origin=direct` = safe). A grant is a ledger transaction of type `admin_grant`, price 0
chips — full audit of rewards.

**Per-user financial report** in the admin console `/_gm` — segment balances, payments,
spends, grants, refunds, full history — as an extension of the existing user card
(`UserDetailView`, `handlers_admin_console.go`). Plus a ledger export.

## 12. Taxes and compliance

Receipts are automatic **through the provider**, and differ by rail:

- **Robokassa** (direct) — self-employed НПД receipt on payment.
- **VK** — VK processes Votes through the tax authority itself; nothing to do.
- **TG Stars** — no tax side (for a RU self-employed, Stars are not legally withdrawable = not
  НПД income; accepted, no receipt issued).

**ОРД** (ad marking) for VK ads is handled on VK's side. (Not legal advice — the owner
confirms the exact НПД scheme with a tax advisor.)

## 13. Distribution (native Android)

- **RuStore** — Robokassa/external gate allowed (0%); native = clean `direct` context.
- **Google Play** — direct purchases are **hidden**; the Wallet shows a stub ("install the
  RuStore build to make purchases"). Rewarded ads and spending already-earned chips still
  work. Confirm Google's current in-app-currency rules before the GP release.

## 14. Data model (schema `payments`)

The payments domain lives in its **own schema `payments`** in the shared Postgres instance,
with its own DB role (rights limited to `payments`) and a domain package behind a hard
interface. There is **no cross-schema foreign key** to `backend.accounts` — an account id is a
plain value here, kept consistent in code and joined to the tombstoned account /
retained-identities dossier by the stable id. That keeps the chip↔benefit spend atomic
**within `payments`** and the domain extractable into its own database. Durability is **PITR**
(continuous WAL archive), independent of DB topology.

Core tables (final names/columns fixed in `PLAN.md`):

- **ledger** — append-only operations: fund / spend / `admin_grant` / refund; `(provider,
  provider_payment_id)` unique for idempotency; export-ready.
- **balances** — materialized `(account_id, source) → chips`.
- **benefits** — materialized `(account_id, origin)` → no-ads `paid_until`/`forever` +
  hints count.
- **catalog** — atoms + products (soft-deletable), per-method prices, chip-purchase rates,
  rewarded payout.
- **orders** — pending purchases, `order_id`, expected amount, origin, status
  (pending/paid/expired).
- **payment_events** — succeeded/failed/refunded for the dispatcher.

Legacy `accounts.hint_balance` and `accounts.paid_account` are **deprecated** in favour of the
segmented model and dropped in a later **contract-phase** migration (expand-contract, after the
currency core flips reads and Release 2 — image rollback stays DB-safe); neither was ever set in
prod (no purchase flow existed), so legacy values are zeroed.

## 15. Glossary

- **Фишка / chip** — the in-game currency; uniform unit, segmented by `source`.
- **source** — where chips were funded (`vk`/`telegram`/`direct`).
- **origin** — where a value was bought; governs where the benefit applies.
- **value / benefit** — what chips buy (no-ads, hints, tournament fee).
- **gate** — the one-directional store-compliance rule (§4).
- **ledger** — the append-only record of all money/value operations.
- **rail** — a payment provider (Robokassa / VK Votes / TG Stars).