feat(payments): chip wallet, store-compliance gate and benefit application

Stand up the internal chip/benefit mechanic behind the narrow payments interface:
context-aware balances and benefits, an atomic chip spend, admin grants as
zero-price value sales, the one-directional store-compliance gate (VK/TG same-
origin only, web draws direct→vk→tg, VK-iOS frozen, untrusted fail-closed), and
per-origin hint and no-ads application with term stacking. Reads are served from
an in-process, account-keyed write-through cache (mirroring the suspension gate),
so hot paths issue no query to the payments schema.

Flip the online-game hint wallet and the ad-banner suppression from the deprecated
accounts.hint_balance / paid_account columns to the payments benefit (a hint
balance no longer suppresses the banner — only a no-ads benefit does), and fold
chip segments and benefits by origin on account merge, inside the merge tx. Add
the GET/POST /api/v1/user/wallet edge chain (REST → Connect → FlatBuffers) plus
its codec unit test; no wallet UI yet.

Bring the frozen owner decisions log into the repo at
docs/PAYMENTS_DECISIONS_ru.md (it was untracked under .vscode) and reference it
from PLAN.md; record the read-cache design and the present-sources interface in
PLAN.md and docs/PAYMENTS.md (+ RU mirror).

backend/internal/payments/cache.go

@@ -0,0 +1,72 @@
+package payments
+
+import (
+	"sync"
+	"time"
+
+	"github.com/google/uuid"
+)
+
+// benefitState is an account's benefit row for one origin: the no-ads term end (nil = none),
+// the perpetual forever flag, and the hint count. It is the context-independent stored form;
+// the read paths aggregate it over the origins applicable in a context.
+type benefitState struct {
+	adsPaidUntil *time.Time
+	adsForever   bool
+	hints        int
+}
+
+// walletState is an account's full payments state: chip balances by source and benefits by
+// origin. It is the raw, context-independent data every read path filters per execution
+// context — the value the cache holds and the store recomputes from the materialized tables.
+type walletState struct {
+	chips    map[Source]int
+	benefits map[Source]benefitState
+}
+
+// chipsOf returns the chip balance for a source, zero when the segment has no row (an absent
+// segment reads as zero, §2).
+func (w walletState) chipsOf(s Source) int { return w.chips[s] }
+
+// benefitOf returns the benefit for an origin, the zero benefit when the origin has no row.
+func (w walletState) benefitOf(o Source) benefitState { return w.benefits[o] }
+
+// walletCache is the payments read model: each account's chip/benefit state, keyed by account
+// id, read on every ad-eligibility / hint / wallet / gate request and invalidated on every
+// payments mutation (spend, grant, fund, refund, merge). It is a write-through cache in front
+// of the materialized balances/benefits tables — the same pattern the account-suspension gate
+// uses (backend/internal/account/suspension.go) — so the steady-state hot path issues no query
+// to the payments schema. It is single-instance, matching the deployment (one shared Store); a
+// multi-instance backend would need a shared cache.
+type walletCache struct {
+	mu sync.RWMutex
+	m  map[uuid.UUID]walletState
+}
+
+// newWalletCache constructs an empty cache.
+func newWalletCache() *walletCache {
+	return &walletCache{m: make(map[uuid.UUID]walletState)}
+}
+
+// get returns the cached state for an account and whether it was present.
+func (c *walletCache) get(id uuid.UUID) (walletState, bool) {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	s, ok := c.m[id]
+	return s, ok
+}
+
+// put stores an account's state.
+func (c *walletCache) put(id uuid.UUID, s walletState) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.m[id] = s
+}
+
+// invalidate drops an account's entry so the next read reloads it from the materialized tables.
+// Called after every mutation once its transaction has committed.
+func (c *walletCache) invalidate(id uuid.UUID) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	delete(c.m, id)
+}

backend/internal/payments/gate.go

@@ -0,0 +1,202 @@
+package payments
+
+import (
+	"slices"
+	"time"
+)
+
+// Source is the platform axis a chip balance is segmented by (where it was funded) and a
+// benefit is stamped with (where it was bought — its origin). The two roles share this value
+// set but mean different things (see docs/PAYMENTS.md §3); Source names the axis for both.
+type Source string
+
+const (
+	// SourceVK is the VK platform: Votes purchases and VK rewarded ads fund here.
+	SourceVK Source = "vk"
+	// SourceTelegram is the Telegram platform: Stars purchases fund here.
+	SourceTelegram Source = "telegram"
+	// SourceDirect is the open web / native context: Robokassa purchases fund here.
+	SourceDirect Source = "direct"
+)
+
+// Valid reports whether s is one of the three known platform sources.
+func (s Source) Valid() bool {
+	switch s {
+	case SourceVK, SourceTelegram, SourceDirect:
+		return true
+	default:
+		return false
+	}
+}
+
+// SubtypeIOS is the one device subtype the gate keys on: VK on iOS is frozen for spending
+// (Apple forbids spending virtual currency on digital goods outside IAP). It is trusted only
+// for VK, where it rides inside the signed launch parameters.
+const SubtypeIOS = "ios"
+
+// SourceForIdentityKind maps a backend identity kind to the payments source whose segment that
+// identity makes available: a vk/telegram identity to its own source, a durable email identity
+// to the direct source (the web/native recovery anchor). A robot identity — or any unknown
+// kind — maps to no source (second return false). Callers use it to build the present set the
+// payments interface takes, since payments cannot read the account schema.
+func SourceForIdentityKind(kind string) (Source, bool) {
+	switch kind {
+	case "vk":
+		return SourceVK, true
+	case "telegram":
+		return SourceTelegram, true
+	case "email":
+		return SourceDirect, true
+	default:
+		return "", false
+	}
+}
+
+// PresentSources maps an account's identity kinds to the payments sources they make available
+// (§6), de-duplicated: vk→vk, telegram→telegram, email→direct; a robot or unknown kind maps to
+// nothing. Callers pass the kinds from account.Identities so the gate — which holds no
+// cross-schema identity knowledge — can resolve which segments are awake.
+func PresentSources(kinds []string) []Source {
+	var out []Source
+	for _, k := range kinds {
+		if s, ok := SourceForIdentityKind(k); ok && !has(out, s) {
+			out = append(out, s)
+		}
+	}
+	return out
+}
+
+// Context is the trusted execution context the store-compliance gate keys on: the platform
+// Kind (the source the wrapper enforces) plus, for VK, the trusted Subtype (only the VK-iOS
+// freeze depends on it). The zero Context (empty Kind) is an untrusted platform — the gate is
+// fail-closed there: no spend, no purchase, no foreign-origin benefit, view only.
+type Context struct {
+	Kind    Source
+	Subtype string
+}
+
+// NewContext builds a Context from the session platform's kind and subtype strings (as carried
+// on the trusted X-Platform signal). An unrecognised or empty kind yields an untrusted Context.
+func NewContext(kind, subtype string) Context {
+	k := Source(kind)
+	if !k.Valid() {
+		return Context{}
+	}
+	return Context{Kind: k, Subtype: subtype}
+}
+
+// Trusted reports whether the platform is trusted (a known kind). An untrusted context denies
+// every spend/purchase and the application of any foreign origin.
+func (c Context) Trusted() bool { return c.Kind.Valid() }
+
+// vkFrozen reports whether this is the VK-iOS spend freeze: VK context on the trusted iOS
+// subtype. A previously bought benefit still applies there, but no spend or purchase is possible.
+func (c Context) vkFrozen() bool { return c.Kind == SourceVK && c.Subtype == SubtypeIOS }
+
+// spendPriority is the fixed draw order when several segments are spendable in one context
+// (D7): the "home" direct segment first, the store-funded segments after.
+var spendPriority = []Source{SourceDirect, SourceVK, SourceTelegram}
+
+// has reports whether present contains s.
+func has(present []Source, s Source) bool {
+	return slices.Contains(present, s)
+}
+
+// spendableSources returns the chip segments that may be SPENT in the context, in draw-priority
+// order, restricted to the sources the account actually has (present). It is empty when the
+// platform is untrusted (fail-closed) or VK-iOS (frozen): inside VK/TG only the same-named
+// segment is spendable; on web/native all attached segments are, drained direct→vk→tg.
+func spendableSources(c Context, present []Source) []Source {
+	if !c.Trusted() || c.vkFrozen() {
+		return nil
+	}
+	switch c.Kind {
+	case SourceVK, SourceTelegram:
+		if has(present, c.Kind) {
+			return []Source{c.Kind}
+		}
+		return nil
+	default: // direct (web/native)
+		var out []Source
+		for _, s := range spendPriority {
+			if has(present, s) {
+				out = append(out, s)
+			}
+		}
+		return out
+	}
+}
+
+// applicableOrigins returns the benefit origins that APPLY in the context, in draw-priority
+// order, restricted to present sources. It differs from spendableSources in one way: VK-iOS is
+// NOT excluded — a benefit bought earlier still applies while spending is frozen. Inside VK/TG
+// only the same-named origin applies (a foreign, e.g. direct, origin never activates inside a
+// store — the compliance wall); on web/native direct+vk+tg all apply, drained direct→vk→tg.
+func applicableOrigins(c Context, present []Source) []Source {
+	if !c.Trusted() {
+		return nil
+	}
+	switch c.Kind {
+	case SourceVK, SourceTelegram:
+		if has(present, c.Kind) {
+			return []Source{c.Kind}
+		}
+		return nil
+	default: // direct (web/native)
+		var out []Source
+		for _, s := range spendPriority {
+			if has(present, s) {
+				out = append(out, s)
+			}
+		}
+		return out
+	}
+}
+
+// visibleSources returns the segments the wallet shows in the context, regardless of whether
+// they are spendable: inside a store only the same-named segment (the others are invisible
+// there); on web/native or an untrusted context all three (untrusted shows them view-only).
+func visibleSources(c Context) []Source {
+	switch c.Kind {
+	case SourceVK, SourceTelegram:
+		return []Source{c.Kind}
+	default:
+		return spendPriority
+	}
+}
+
+// Segment is one chip balance the wallet shows: the source, its chip count, and whether it can
+// be spent in the current context (false for a frozen VK-iOS balance or an untrusted platform).
+type Segment struct {
+	Source    Source
+	Chips     int
+	Spendable bool
+}
+
+// BenefitView is the benefit state applicable in the current context: whether ads are off (and
+// until when, or forever) and how many hints are available. It aggregates over the origins
+// applicable in the context (§5).
+type BenefitView struct {
+	AdsForever   bool
+	AdsPaidUntil *time.Time
+	Hints        int
+}
+
+// WalletView is the read model returned to the wallet: the visible segments plus the
+// context-applicable benefits.
+type WalletView struct {
+	Segments []Segment
+	Benefits BenefitView
+}
+
+// benefitDelta is the benefit change a spend or grant applies to one origin: hints added, a
+// no-ads term in whole days (stacked from max(now, current end)), and the perpetual forever
+// flag (which overrides terms).
+type benefitDelta struct {
+	hintsAdd  int
+	noAdsDays int
+	forever   bool
+}
+
+// zero reports whether the delta changes nothing.
+func (d benefitDelta) zero() bool { return d.hintsAdd == 0 && d.noAdsDays == 0 && !d.forever }

backend/internal/payments/gate_test.go

@@ -0,0 +1,132 @@
+package payments
+
+import (
+	"slices"
+	"testing"
+)
+
+// allPresent is an account attached to every source (the maximal present set).
+var allPresent = []Source{SourceDirect, SourceVK, SourceTelegram}
+
+func TestSpendableSources(t *testing.T) {
+	tests := []struct {
+		name    string
+		ctx     Context
+		present []Source
+		want    []Source
+	}{
+		{"vk android, vk present", Context{Kind: SourceVK, Subtype: "android"}, allPresent, []Source{SourceVK}},
+		{"vk ios frozen", Context{Kind: SourceVK, Subtype: SubtypeIOS}, allPresent, nil},
+		{"vk android, vk absent", Context{Kind: SourceVK, Subtype: "android"}, []Source{SourceDirect}, nil},
+		{"telegram", Context{Kind: SourceTelegram, Subtype: "web"}, allPresent, []Source{SourceTelegram}},
+		{"telegram, tg absent", Context{Kind: SourceTelegram}, []Source{SourceVK}, nil},
+		{"direct all present, priority", Context{Kind: SourceDirect, Subtype: "web"}, allPresent, []Source{SourceDirect, SourceVK, SourceTelegram}},
+		{"direct, only vk+tg attached", Context{Kind: SourceDirect}, []Source{SourceTelegram, SourceVK}, []Source{SourceVK, SourceTelegram}},
+		{"direct, nothing attached", Context{Kind: SourceDirect}, nil, nil},
+		{"untrusted fail-closed", Context{}, allPresent, nil},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := spendableSources(tc.ctx, tc.present); !slices.Equal(got, tc.want) {
+				t.Errorf("spendableSources(%+v, %v) = %v, want %v", tc.ctx, tc.present, got, tc.want)
+			}
+		})
+	}
+}
+
+func TestApplicableOrigins(t *testing.T) {
+	tests := []struct {
+		name    string
+		ctx     Context
+		present []Source
+		want    []Source
+	}{
+		// A benefit still APPLIES on VK-iOS while spending is frozen.
+		{"vk ios still applies", Context{Kind: SourceVK, Subtype: SubtypeIOS}, allPresent, []Source{SourceVK}},
+		{"vk android", Context{Kind: SourceVK, Subtype: "android"}, allPresent, []Source{SourceVK}},
+		{"telegram", Context{Kind: SourceTelegram}, allPresent, []Source{SourceTelegram}},
+		{"direct all, priority", Context{Kind: SourceDirect}, allPresent, []Source{SourceDirect, SourceVK, SourceTelegram}},
+		{"untrusted fail-closed", Context{}, allPresent, nil},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := applicableOrigins(tc.ctx, tc.present); !slices.Equal(got, tc.want) {
+				t.Errorf("applicableOrigins(%+v, %v) = %v, want %v", tc.ctx, tc.present, got, tc.want)
+			}
+		})
+	}
+}
+
+// TestComplianceWall is the named unit-level compliance regression: a direct origin (externally
+// paid, outside any store cash desk) must NEVER be applicable inside a VK or TG wrapper, and no
+// segment is ever spendable there beyond the same-named one. The dangerous direction stays shut.
+func TestComplianceWall(t *testing.T) {
+	for _, kind := range []Source{SourceVK, SourceTelegram} {
+		for _, sub := range []string{"android", "ios", "web"} {
+			ctx := Context{Kind: kind, Subtype: sub}
+			if slices.Contains(applicableOrigins(ctx, allPresent), SourceDirect) {
+				t.Errorf("direct origin applies inside %s/%s — compliance wall breached", kind, sub)
+			}
+			for _, s := range spendableSources(ctx, allPresent) {
+				if s != kind {
+					t.Errorf("foreign segment %s spendable inside %s/%s", s, kind, sub)
+				}
+			}
+			// The opposite store's origin must not leak in either (vk⊥tg).
+			other := SourceVK
+			if kind == SourceVK {
+				other = SourceTelegram
+			}
+			if slices.Contains(applicableOrigins(ctx, allPresent), other) {
+				t.Errorf("%s origin applies inside %s — cross-store leak", other, kind)
+			}
+		}
+	}
+}
+
+func TestVisibleSources(t *testing.T) {
+	if got := visibleSources(Context{Kind: SourceVK, Subtype: SubtypeIOS}); !slices.Equal(got, []Source{SourceVK}) {
+		t.Errorf("VK visible = %v, want [vk] (direct/tg hidden in a store)", got)
+	}
+	if got := visibleSources(Context{Kind: SourceDirect}); !slices.Equal(got, allPresent) {
+		t.Errorf("direct visible = %v, want all three", got)
+	}
+	if got := visibleSources(Context{}); !slices.Equal(got, allPresent) {
+		t.Errorf("untrusted visible = %v, want all three (view-only)", got)
+	}
+}
+
+func TestSourceForIdentityKind(t *testing.T) {
+	tests := []struct {
+		kind string
+		want Source
+		ok   bool
+	}{
+		{"vk", SourceVK, true},
+		{"telegram", SourceTelegram, true},
+		{"email", SourceDirect, true},
+		{"robot", "", false},
+		{"unknown", "", false},
+	}
+	for _, tc := range tests {
+		got, ok := SourceForIdentityKind(tc.kind)
+		if got != tc.want || ok != tc.ok {
+			t.Errorf("SourceForIdentityKind(%q) = %q,%v want %q,%v", tc.kind, got, ok, tc.want, tc.ok)
+		}
+	}
+}
+
+func TestNewContextTrusted(t *testing.T) {
+	if c := NewContext("vk", "ios"); !c.Trusted() || !c.vkFrozen() {
+		t.Errorf("vk/ios: trusted=%v frozen=%v, want true/true", c.Trusted(), c.vkFrozen())
+	}
+	if c := NewContext("bogus", "web"); c.Trusted() {
+		t.Errorf("bogus kind should be untrusted")
+	}
+	if c := NewContext("", ""); c.Trusted() {
+		t.Errorf("empty kind should be untrusted")
+	}
+	if c := NewContext("direct", "web"); c.vkFrozen() {
+		t.Errorf("direct is never frozen")
+	}
+}

backend/internal/payments/service.go

@@ -1,17 +1,234 @@
 package payments
 
-import "context"
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"fmt"
+	"time"
 
-// Service is the payments domain's application layer — the narrow surface other
-// domains depend on, keeping the schema reachable through one seam. The
-// data-foundation layer exposes only a health check; the wallet, benefit and
-// store-compliance operations arrive with the currency mechanics.
+	"github.com/google/uuid"
+)
+
+// Service is the payments domain's application layer — the narrow surface other domains depend
+// on, keeping the schema reachable through one seam. Every read/gate method takes the trusted
+// execution Context and the account's present identity sources (which segments are awake, §6);
+// payments holds no cross-schema identity knowledge, so the caller supplies present. Reads are
+// served from the store's in-process cache, so the steady-state hot path issues no query to the
+// payments schema.
 type Service struct {
 	store *Store
+	clock func() time.Time
 }
 
-// NewService constructs a Service over store.
-func NewService(store *Store) *Service { return &Service{store: store} }
+// NewService constructs a Service over store with a wall-clock time source.
+func NewService(store *Store) *Service {
+	return &Service{store: store, clock: func() time.Time { return time.Now().UTC() }}
+}
 
 // Ping reports whether the payments schema is reachable.
 func (s *Service) Ping(ctx context.Context) error { return s.store.Ping(ctx) }
+
+// Wallet returns the read model for the account in the execution context: the segments visible
+// there (each with its chip count and whether it is spendable) plus the context-applicable
+// benefits. In a store context only the same-named segment is shown; on web/native or an
+// untrusted platform all attached segments are shown, spendable only when the gate allows.
+func (s *Service) Wallet(ctx context.Context, accountID uuid.UUID, cxt Context, present []Source) (WalletView, error) {
+	st, err := s.store.state(ctx, accountID)
+	if err != nil {
+		return WalletView{}, err
+	}
+	now := s.clock()
+	view := WalletView{Benefits: benefitView(st, cxt, present, now)}
+	spendable := spendableSources(cxt, present)
+	for _, src := range visibleSources(cxt) {
+		if !has(present, src) {
+			continue // only the account's own (attached) segments are shown
+		}
+		view.Segments = append(view.Segments, Segment{
+			Source:    src,
+			Chips:     st.chipsOf(src),
+			Spendable: has(spendable, src),
+		})
+	}
+	return view, nil
+}
+
+// AdFree reports whether ads are suppressed for the account in the context: some origin
+// applicable there has an active no-ads term or the forever flag. Fail-closed on an untrusted
+// platform (no origin applies).
+func (s *Service) AdFree(ctx context.Context, accountID uuid.UUID, cxt Context, present []Source) (bool, error) {
+	st, err := s.store.state(ctx, accountID)
+	if err != nil {
+		return false, err
+	}
+	now := s.clock()
+	for _, o := range applicableOrigins(cxt, present) {
+		b := st.benefitOf(o)
+		if b.adsForever || (b.adsPaidUntil != nil && b.adsPaidUntil.After(now)) {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+// HintsAvailable returns how many hints the account can use in the context — the sum over the
+// applicable origins. Zero on an untrusted platform.
+func (s *Service) HintsAvailable(ctx context.Context, accountID uuid.UUID, cxt Context, present []Source) (int, error) {
+	st, err := s.store.state(ctx, accountID)
+	if err != nil {
+		return 0, err
+	}
+	total := 0
+	for _, o := range applicableOrigins(cxt, present) {
+		total += st.benefitOf(o).hints
+	}
+	return total, nil
+}
+
+// SpendHint consumes one hint from the first applicable origin that has one (priority
+// direct→vk→tg), returning whether a hint was spent. It spends nothing when no origin is
+// applicable (untrusted platform or no attached segment).
+func (s *Service) SpendHint(ctx context.Context, accountID uuid.UUID, cxt Context, present []Source) (bool, error) {
+	origins := applicableOrigins(cxt, present)
+	if len(origins) == 0 {
+		return false, nil
+	}
+	return s.store.consumeHint(ctx, accountID, origins, s.clock())
+}
+
+// Spend buys a chip-priced value: it gate-checks the context, draws the price across the
+// spendable segments by priority direct→vk→tg, and applies the benefit — atomically. The
+// benefit's origin is the purchase context. It fails closed on an untrusted or frozen platform
+// (ErrUntrusted) and on insufficient chips (ErrInsufficientChips).
+func (s *Service) Spend(ctx context.Context, accountID uuid.UUID, cxt Context, present []Source, productID uuid.UUID) error {
+	spendable := spendableSources(cxt, present)
+	if len(spendable) == 0 {
+		return ErrUntrusted // untrusted, frozen, or no attached segment — no spend
+	}
+	prod, err := s.store.loadProduct(ctx, productID)
+	if err != nil {
+		return err
+	}
+	st, err := s.store.state(ctx, accountID)
+	if err != nil {
+		return err
+	}
+	draws, ok := planDraws(st, spendable, prod.priceChips)
+	if !ok {
+		return ErrInsufficientChips
+	}
+	snapshot, err := marshalSnapshot(prod)
+	if err != nil {
+		return err
+	}
+	return s.store.spend(ctx, accountID, draws, cxt.Kind, productID, prod.delta, snapshot, s.clock())
+}
+
+// Grant applies a benefit to an origin as a zero-price sale — an admin_grant ledger row and the
+// benefit (hints, a no-ads term in whole days, or the forever flag). It never grants chips (no
+// balance is touched — D16), so its signature has no chip amount. The origin is the admin's
+// compliance choice.
+func (s *Service) Grant(ctx context.Context, accountID uuid.UUID, origin Source, hints, noAdsDays int, forever bool) error {
+	if !origin.Valid() {
+		return fmt.Errorf("payments: invalid grant origin %q", origin)
+	}
+	d := benefitDelta{hintsAdd: hints, noAdsDays: noAdsDays, forever: forever}
+	if d.zero() {
+		return fmt.Errorf("payments: empty grant")
+	}
+	snapshot, err := marshalGrant(d)
+	if err != nil {
+		return err
+	}
+	return s.store.grant(ctx, accountID, origin, d, snapshot, s.clock())
+}
+
+// MergeTx merges the secondary account's segments and benefits into the primary inside the
+// caller's transaction (the account-merge flow). The caller invalidates the affected caches
+// after committing (Invalidate).
+func (s *Service) MergeTx(ctx context.Context, tx *sql.Tx, primary, secondary uuid.UUID) error {
+	return s.store.MergeTx(ctx, tx, primary, secondary, s.clock())
+}
+
+// Invalidate drops the cached state of the listed accounts (called after a merge commit).
+func (s *Service) Invalidate(ids ...uuid.UUID) { s.store.Invalidate(ids...) }
+
+// benefitView aggregates the benefits applicable in the context into the wallet view: ads-off
+// forever if any applicable origin is perpetual, else the latest active term end, plus the total
+// available hints.
+func benefitView(st walletState, cxt Context, present []Source, now time.Time) BenefitView {
+	var v BenefitView
+	for _, o := range applicableOrigins(cxt, present) {
+		b := st.benefitOf(o)
+		if b.adsForever {
+			v.AdsForever = true
+		}
+		if b.adsPaidUntil != nil && b.adsPaidUntil.After(now) {
+			if v.AdsPaidUntil == nil || b.adsPaidUntil.After(*v.AdsPaidUntil) {
+				v.AdsPaidUntil = b.adsPaidUntil
+			}
+		}
+		v.Hints += b.hints
+	}
+	return v
+}
+
+// planDraws greedily allocates price across the spendable segments in priority order, draining
+// each before moving on. It returns the per-segment draws and whether the segments together held
+// enough.
+func planDraws(st walletState, spendable []Source, price int) ([]sourceAmount, bool) {
+	remaining := price
+	var draws []sourceAmount
+	for _, src := range spendable {
+		if remaining <= 0 {
+			break
+		}
+		avail := st.chipsOf(src)
+		if avail <= 0 {
+			continue
+		}
+		take := min(avail, remaining)
+		draws = append(draws, sourceAmount{source: src, amount: take})
+		remaining -= take
+	}
+	if remaining > 0 {
+		return nil, false
+	}
+	return draws, true
+}
+
+// purchaseSnapshot is the catalog snapshot stored on a spend/grant ledger row, so history and
+// receipts stay independent of later catalog edits (§7/D34).
+type purchaseSnapshot struct {
+	ProductID  string         `json:"product_id,omitempty"`
+	Title      string         `json:"title,omitempty"`
+	Atoms      map[string]int `json:"atoms,omitempty"`
+	PriceChips int            `json:"price_chips"`
+	Forever    bool           `json:"forever,omitempty"`
+}
+
+// marshalSnapshot builds the snapshot for a chip spend.
+func marshalSnapshot(p catalogProduct) ([]byte, error) {
+	b, err := json.Marshal(purchaseSnapshot{ProductID: p.id.String(), Title: p.title, Atoms: p.atoms, PriceChips: p.priceChips})
+	if err != nil {
+		return nil, fmt.Errorf("payments: marshal snapshot: %w", err)
+	}
+	return b, nil
+}
+
+// marshalGrant builds the snapshot for an admin grant (price 0).
+func marshalGrant(d benefitDelta) ([]byte, error) {
+	atoms := map[string]int{}
+	if d.hintsAdd > 0 {
+		atoms["hints"] = d.hintsAdd
+	}
+	if d.noAdsDays > 0 {
+		atoms["noads_days"] = d.noAdsDays
+	}
+	b, err := json.Marshal(purchaseSnapshot{Atoms: atoms, PriceChips: 0, Forever: d.forever})
+	if err != nil {
+		return nil, fmt.Errorf("payments: marshal grant snapshot: %w", err)
+	}
+	return b, nil
+}

backend/internal/payments/store.go

@@ -14,13 +14,16 @@ import (
 // Store is the Postgres-backed query surface for the payments schema. It is the
 // only place in the backend that issues SQL against payments.* (an
 // import-boundary test enforces it), so the domain stays extractable into its
-// own database.
+// own database. It fronts the materialized balances/benefits tables with an
+// in-process write-through cache (see cache.go) so hot reads issue no query on
+// the steady-state path.
 type Store struct {
-	db *sql.DB
+	db    *sql.DB
+	cache *walletCache
 }
 
-// NewStore constructs a Store wrapping db.
-func NewStore(db *sql.DB) *Store { return &Store{db: db} }
+// NewStore constructs a Store wrapping db, with an empty read cache.
+func NewStore(db *sql.DB) *Store { return &Store{db: db, cache: newWalletCache()} }
 
 // Ping verifies the payments schema is reachable by reading the singleton config
 // row. It is the data-foundation health check; the wallet query surface arrives

backend/internal/payments/store_wallet.go

@@ -0,0 +1,421 @@
+package payments
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/go-jet/jet/v2/postgres"
+	"github.com/go-jet/jet/v2/qrm"
+	"github.com/google/uuid"
+
+	"scrabble/backend/internal/postgres/jet/payments/model"
+	"scrabble/backend/internal/postgres/jet/payments/table"
+)
+
+// Domain errors surfaced by the payments store and service.
+var (
+	// ErrInsufficientChips means the spendable segments held fewer chips than the price.
+	ErrInsufficientChips = errors.New("payments: insufficient chips")
+	// ErrUntrusted means the platform context is untrusted, so the gate is fail-closed.
+	ErrUntrusted = errors.New("payments: untrusted platform")
+	// ErrProductNotFound means the product is absent or deactivated.
+	ErrProductNotFound = errors.New("payments: product not found")
+	// ErrNotAValue means the product has no chip price (it is a chip pack or unpriced), so it
+	// cannot be bought with chips.
+	ErrNotAValue = errors.New("payments: product is not a chip-priced value")
+)
+
+// withTx runs fn inside a transaction on db, rolling back on error or panic.
+func withTx(ctx context.Context, db *sql.DB, fn func(*sql.Tx) error) (err error) {
+	tx, err := db.BeginTx(ctx, nil)
+	if err != nil {
+		return fmt.Errorf("payments: begin tx: %w", err)
+	}
+	defer func() {
+		if p := recover(); p != nil {
+			_ = tx.Rollback()
+			panic(p)
+		}
+	}()
+	if err := fn(tx); err != nil {
+		_ = tx.Rollback()
+		return err
+	}
+	if err := tx.Commit(); err != nil {
+		return fmt.Errorf("payments: commit tx: %w", err)
+	}
+	return nil
+}
+
+// sourceAmount is one chip draw from a single segment during a spend.
+type sourceAmount struct {
+	source Source
+	amount int
+}
+
+// catalogProduct is a product resolved for a chip spend: its chip price, the benefit its atoms
+// fold into, and the raw atom composition for the purchase snapshot.
+type catalogProduct struct {
+	id         uuid.UUID
+	title      string
+	priceChips int
+	delta      benefitDelta
+	atoms      map[string]int
+}
+
+// loadState reads an account's balances and benefits straight from the materialized tables.
+func (s *Store) loadState(ctx context.Context, accountID uuid.UUID) (walletState, error) {
+	st := walletState{chips: map[Source]int{}, benefits: map[Source]benefitState{}}
+	var brows []model.Balances
+	if err := postgres.SELECT(table.Balances.AllColumns).
+		FROM(table.Balances).
+		WHERE(table.Balances.AccountID.EQ(postgres.UUID(accountID))).
+		QueryContext(ctx, s.db, &brows); err != nil {
+		return walletState{}, fmt.Errorf("payments: load balances %s: %w", accountID, err)
+	}
+	for _, r := range brows {
+		st.chips[Source(r.Source)] = int(r.Chips)
+	}
+	var frows []model.Benefits
+	if err := postgres.SELECT(table.Benefits.AllColumns).
+		FROM(table.Benefits).
+		WHERE(table.Benefits.AccountID.EQ(postgres.UUID(accountID))).
+		QueryContext(ctx, s.db, &frows); err != nil {
+		return walletState{}, fmt.Errorf("payments: load benefits %s: %w", accountID, err)
+	}
+	for _, r := range frows {
+		st.benefits[Source(r.Origin)] = benefitState{adsPaidUntil: r.AdsPaidUntil, adsForever: r.AdsForever, hints: int(r.Hints)}
+	}
+	return st, nil
+}
+
+// state returns an account's payments state, served from the read cache when warm, otherwise
+// loaded from the materialized tables and cached. The returned maps are read-only.
+func (s *Store) state(ctx context.Context, accountID uuid.UUID) (walletState, error) {
+	if st, ok := s.cache.get(accountID); ok {
+		return st, nil
+	}
+	st, err := s.loadState(ctx, accountID)
+	if err != nil {
+		return walletState{}, err
+	}
+	s.cache.put(accountID, st)
+	return st, nil
+}
+
+// Invalidate drops the cached state of every listed account so the next read reloads it. It is
+// called after a committed mutation whose transaction the payments package does not own — the
+// account-merge flow (after its own commit) and, later, external fund/refund intake.
+func (s *Store) Invalidate(ids ...uuid.UUID) {
+	for _, id := range ids {
+		s.cache.invalidate(id)
+	}
+}
+
+// loadProduct resolves a chip-priced value: an active product with a CHIP price row
+// (method NULL) whose atoms are benefits (hints / no-ads days). It rejects a missing or
+// deactivated product (ErrProductNotFound), a product with no chip price (ErrNotAValue), and a
+// product carrying the chips atom (a chip pack is funded, never bought with chips — ErrNotAValue).
+func (s *Store) loadProduct(ctx context.Context, productID uuid.UUID) (catalogProduct, error) {
+	var p model.Product
+	err := postgres.SELECT(table.Product.AllColumns).
+		FROM(table.Product).
+		WHERE(table.Product.ProductID.EQ(postgres.UUID(productID))).
+		LIMIT(1).
+		QueryContext(ctx, s.db, &p)
+	if errors.Is(err, qrm.ErrNoRows) || (err == nil && !p.Active) {
+		return catalogProduct{}, ErrProductNotFound
+	}
+	if err != nil {
+		return catalogProduct{}, fmt.Errorf("payments: load product %s: %w", productID, err)
+	}
+
+	var price model.ProductPrice
+	err = postgres.SELECT(table.ProductPrice.AllColumns).
+		FROM(table.ProductPrice).
+		WHERE(table.ProductPrice.ProductID.EQ(postgres.UUID(productID)).
+			AND(table.ProductPrice.Method.IS_NULL()).
+			AND(table.ProductPrice.Currency.EQ(postgres.String(string(CurrencyChip))))).
+		LIMIT(1).
+		QueryContext(ctx, s.db, &price)
+	if errors.Is(err, qrm.ErrNoRows) {
+		return catalogProduct{}, ErrNotAValue
+	}
+	if err != nil {
+		return catalogProduct{}, fmt.Errorf("payments: load price %s: %w", productID, err)
+	}
+
+	var items []model.ProductItem
+	if err := postgres.SELECT(table.ProductItem.AllColumns).
+		FROM(table.ProductItem).
+		WHERE(table.ProductItem.ProductID.EQ(postgres.UUID(productID))).
+		QueryContext(ctx, s.db, &items); err != nil {
+		return catalogProduct{}, fmt.Errorf("payments: load items %s: %w", productID, err)
+	}
+
+	cp := catalogProduct{id: productID, title: p.Title, priceChips: int(price.Amount), atoms: map[string]int{}}
+	for _, it := range items {
+		cp.atoms[it.AtomType] = int(it.Quantity)
+		switch it.AtomType {
+		case "hints":
+			cp.delta.hintsAdd += int(it.Quantity)
+		case "noads_days":
+			cp.delta.noAdsDays += int(it.Quantity)
+		case "chips":
+			return catalogProduct{}, ErrNotAValue // a value never grants chips
+		}
+	}
+	return cp, nil
+}
+
+// stackNoAds returns the new no-ads term end after adding addDays whole days from
+// max(now, current end) — terms add up, the remainder is never lost (§5/D33). A non-positive
+// addDays leaves the term unchanged; a nil current means no term yet.
+func stackNoAds(current *time.Time, addDays int, now time.Time) *time.Time {
+	if addDays <= 0 {
+		return current
+	}
+	base := now
+	if current != nil && current.After(now) {
+		base = *current
+	}
+	end := base.Add(time.Duration(addDays) * 24 * time.Hour)
+	return &end
+}
+
+// combineNoAds folds secondary's remaining no-ads term onto primary's during a merge: the
+// remaining duration of each is preserved (§6/D15 "terms extend per origin").
+func combineNoAds(primary, secondary *time.Time, now time.Time) *time.Time {
+	if secondary == nil || !secondary.After(now) {
+		return primary
+	}
+	base := now
+	if primary != nil && primary.After(now) {
+		base = *primary
+	}
+	end := base.Add(secondary.Sub(now))
+	return &end
+}
+
+// applyBenefitTx applies a benefit delta to one origin inside tx, stacking the no-ads term,
+// OR-ing the forever flag and adding hints. It ensures the (account, origin) row exists, locks
+// it, then writes the recomputed values — so concurrent applies serialise on the row lock.
+func applyBenefitTx(ctx context.Context, tx *sql.Tx, accountID uuid.UUID, origin Source, d benefitDelta, now time.Time) error {
+	if d.zero() {
+		return nil
+	}
+	if _, err := tx.ExecContext(ctx,
+		`INSERT INTO payments.benefits (account_id, origin) VALUES ($1, $2) ON CONFLICT DO NOTHING`,
+		accountID, string(origin)); err != nil {
+		return fmt.Errorf("payments: ensure benefit row %s: %w", origin, err)
+	}
+	var untilCur *time.Time
+	var foreverCur bool
+	var hintsCur int32
+	if err := tx.QueryRowContext(ctx,
+		`SELECT ads_paid_until, ads_forever, hints FROM payments.benefits
+		 WHERE account_id = $1 AND origin = $2 FOR UPDATE`, accountID, string(origin)).
+		Scan(&untilCur, &foreverCur, &hintsCur); err != nil {
+		return fmt.Errorf("payments: lock benefit %s: %w", origin, err)
+	}
+	if _, err := tx.ExecContext(ctx,
+		`UPDATE payments.benefits SET ads_paid_until = $3, ads_forever = $4, hints = $5, updated_at = now()
+		 WHERE account_id = $1 AND origin = $2`,
+		accountID, string(origin), stackNoAds(untilCur, d.noAdsDays, now), foreverCur || d.forever, int(hintsCur)+d.hintsAdd); err != nil {
+		return fmt.Errorf("payments: apply benefit %s: %w", origin, err)
+	}
+	return nil
+}
+
+// insertLedgerTx appends one append-only ledger row inside tx.
+func insertLedgerTx(ctx context.Context, tx *sql.Tx, accountID uuid.UUID, kind string, source, origin *Source, chipsDelta int, productID *uuid.UUID, snapshot []byte, now time.Time) error {
+	id, err := uuid.NewV7()
+	if err != nil {
+		return fmt.Errorf("payments: ledger id: %w", err)
+	}
+	// The snapshot is a bare value, not a postgres.String literal: a jsonb column infers its
+	// type from an untyped parameter (the game-moves payload idiom), whereas a text-typed
+	// literal is rejected against jsonb.
+	var snap any = postgres.NULL
+	if snapshot != nil {
+		snap = string(snapshot)
+	}
+	stmt := table.Ledger.INSERT(
+		table.Ledger.LedgerID, table.Ledger.AccountID, table.Ledger.Kind,
+		table.Ledger.Source, table.Ledger.Origin, table.Ledger.ChipsDelta,
+		table.Ledger.ProductID, table.Ledger.Snapshot, table.Ledger.CreatedAt,
+	).VALUES(
+		id, accountID, kind,
+		sourceOrNull(source), sourceOrNull(origin), int32(chipsDelta),
+		uuidOrNull(productID), snap, now,
+	)
+	if _, err := stmt.ExecContext(ctx, tx); err != nil {
+		return fmt.Errorf("payments: insert %s ledger: %w", kind, err)
+	}
+	return nil
+}
+
+// spend draws the chips across the given segments, appends a spend ledger row per draw (carrying
+// the purchase snapshot), and applies the benefit — all in one transaction. It fails closed on
+// an insufficient balance (a guarded decrement), rolling everything back.
+func (s *Store) spend(ctx context.Context, accountID uuid.UUID, draws []sourceAmount, origin Source, productID uuid.UUID, d benefitDelta, snapshot []byte, now time.Time) error {
+	err := withTx(ctx, s.db, func(tx *sql.Tx) error {
+		for _, dr := range draws {
+			res, err := table.Balances.
+				UPDATE(table.Balances.Chips, table.Balances.UpdatedAt).
+				SET(table.Balances.Chips.SUB(postgres.Int(int64(dr.amount))), postgres.TimestampzT(now)).
+				WHERE(table.Balances.AccountID.EQ(postgres.UUID(accountID)).
+					AND(table.Balances.Source.EQ(postgres.String(string(dr.source)))).
+					AND(table.Balances.Chips.GT_EQ(postgres.Int(int64(dr.amount))))).
+				ExecContext(ctx, tx)
+			if err != nil {
+				return fmt.Errorf("payments: decrement %s: %w", dr.source, err)
+			}
+			if n, _ := res.RowsAffected(); n == 0 {
+				return ErrInsufficientChips
+			}
+			src := dr.source
+			if err := insertLedgerTx(ctx, tx, accountID, "spend", &src, &origin, -dr.amount, &productID, snapshot, now); err != nil {
+				return err
+			}
+		}
+		return applyBenefitTx(ctx, tx, accountID, origin, d, now)
+	})
+	if err != nil {
+		return err
+	}
+	s.cache.invalidate(accountID)
+	return nil
+}
+
+// grant records an admin_grant ledger row (price 0, no chips) and applies the granted benefit to
+// the chosen origin, in one transaction — a zero-price sale of a value.
+func (s *Store) grant(ctx context.Context, accountID uuid.UUID, origin Source, d benefitDelta, snapshot []byte, now time.Time) error {
+	err := withTx(ctx, s.db, func(tx *sql.Tx) error {
+		if err := insertLedgerTx(ctx, tx, accountID, "admin_grant", nil, &origin, 0, nil, snapshot, now); err != nil {
+			return err
+		}
+		return applyBenefitTx(ctx, tx, accountID, origin, d, now)
+	})
+	if err != nil {
+		return err
+	}
+	s.cache.invalidate(accountID)
+	return nil
+}
+
+// consumeHint decrements one hint from the first applicable origin (in the given priority order)
+// that has one, with a guarded update. It returns whether a hint was spent.
+func (s *Store) consumeHint(ctx context.Context, accountID uuid.UUID, origins []Source, now time.Time) (bool, error) {
+	for _, o := range origins {
+		res, err := table.Benefits.
+			UPDATE(table.Benefits.Hints, table.Benefits.UpdatedAt).
+			SET(table.Benefits.Hints.SUB(postgres.Int(1)), postgres.TimestampzT(now)).
+			WHERE(table.Benefits.AccountID.EQ(postgres.UUID(accountID)).
+				AND(table.Benefits.Origin.EQ(postgres.String(string(o)))).
+				AND(table.Benefits.Hints.GT(postgres.Int(0)))).
+			ExecContext(ctx, s.db)
+		if err != nil {
+			return false, fmt.Errorf("payments: consume hint %s: %w", o, err)
+		}
+		if n, _ := res.RowsAffected(); n > 0 {
+			s.cache.invalidate(accountID)
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+// MergeTx folds the secondary account's segments and benefits into the primary, by source and by
+// origin, inside the caller's transaction (the account-merge flow): chips sum, no-ads terms
+// extend per origin, forever OR-s, hints add. The secondary's payments rows are removed. The
+// caller invalidates the primary's cache after its own commit (Invalidate). It does not touch
+// the account schema — the JET import boundary stays intact, only the shared connection is used.
+func (s *Store) MergeTx(ctx context.Context, tx *sql.Tx, primary, secondary uuid.UUID, now time.Time) error {
+	if _, err := tx.ExecContext(ctx,
+		`INSERT INTO payments.balances (account_id, source, chips, updated_at)
+		 SELECT $1, source, chips, now() FROM payments.balances WHERE account_id = $2
+		 ON CONFLICT (account_id, source) DO UPDATE
+		   SET chips = payments.balances.chips + EXCLUDED.chips, updated_at = now()`,
+		primary, secondary); err != nil {
+		return fmt.Errorf("payments: merge balances: %w", err)
+	}
+	if _, err := tx.ExecContext(ctx, `DELETE FROM payments.balances WHERE account_id = $1`, secondary); err != nil {
+		return fmt.Errorf("payments: clear secondary balances: %w", err)
+	}
+
+	rows, err := tx.QueryContext(ctx,
+		`SELECT origin, ads_paid_until, ads_forever, hints FROM payments.benefits WHERE account_id = $1`, secondary)
+	if err != nil {
+		return fmt.Errorf("payments: read secondary benefits: %w", err)
+	}
+	type secBenefit struct {
+		origin  Source
+		until   *time.Time
+		forever bool
+		hints   int
+	}
+	var secs []secBenefit
+	for rows.Next() {
+		var b secBenefit
+		var o string
+		var h int32
+		if err := rows.Scan(&o, &b.until, &b.forever, &h); err != nil {
+			rows.Close()
+			return fmt.Errorf("payments: scan secondary benefit: %w", err)
+		}
+		b.origin, b.hints = Source(o), int(h)
+		secs = append(secs, b)
+	}
+	if err := rows.Err(); err != nil {
+		rows.Close()
+		return fmt.Errorf("payments: iterate secondary benefits: %w", err)
+	}
+	rows.Close()
+
+	for _, b := range secs {
+		if _, err := tx.ExecContext(ctx,
+			`INSERT INTO payments.benefits (account_id, origin) VALUES ($1, $2) ON CONFLICT DO NOTHING`,
+			primary, string(b.origin)); err != nil {
+			return fmt.Errorf("payments: ensure primary benefit %s: %w", b.origin, err)
+		}
+		var untilCur *time.Time
+		var foreverCur bool
+		var hintsCur int32
+		if err := tx.QueryRowContext(ctx,
+			`SELECT ads_paid_until, ads_forever, hints FROM payments.benefits
+			 WHERE account_id = $1 AND origin = $2 FOR UPDATE`, primary, string(b.origin)).
+			Scan(&untilCur, &foreverCur, &hintsCur); err != nil {
+			return fmt.Errorf("payments: lock primary benefit %s: %w", b.origin, err)
+		}
+		if _, err := tx.ExecContext(ctx,
+			`UPDATE payments.benefits SET ads_paid_until = $3, ads_forever = $4, hints = $5, updated_at = now()
+			 WHERE account_id = $1 AND origin = $2`,
+			primary, string(b.origin), combineNoAds(untilCur, b.until, now), foreverCur || b.forever, int(hintsCur)+b.hints); err != nil {
+			return fmt.Errorf("payments: merge benefit %s: %w", b.origin, err)
+		}
+	}
+	if _, err := tx.ExecContext(ctx, `DELETE FROM payments.benefits WHERE account_id = $1`, secondary); err != nil {
+		return fmt.Errorf("payments: clear secondary benefits: %w", err)
+	}
+	return nil
+}
+
+// sourceOrNull renders an optional source as a SQL string or NULL.
+func sourceOrNull(s *Source) postgres.Expression {
+	if s == nil {
+		return postgres.NULL
+	}
+	return postgres.String(string(*s))
+}
+
+// uuidOrNull renders an optional id as a SQL uuid or NULL.
+func uuidOrNull(id *uuid.UUID) postgres.Expression {
+	if id == nil {
+		return postgres.NULL
+	}
+	return postgres.UUID(*id)
+}

backend/internal/payments/wallet_test.go

@@ -0,0 +1,182 @@
+package payments
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+)
+
+// base is a fixed clock instant for the deterministic tests.
+var base = time.Date(2026, 7, 8, 12, 0, 0, 0, time.UTC)
+
+// seededService builds a Service whose read cache already holds st for id, so the read methods
+// resolve without a database (the store's db is nil). The clock is pinned to base.
+func seededService(id uuid.UUID, st walletState) *Service {
+	store := NewStore(nil)
+	store.cache.put(id, st)
+	return &Service{store: store, clock: func() time.Time { return base }}
+}
+
+func TestStackNoAds(t *testing.T) {
+	future := base.Add(48 * time.Hour)
+	past := base.Add(-time.Hour)
+	tests := []struct {
+		name    string
+		current *time.Time
+		addDays int
+		want    *time.Time
+	}{
+		{"fresh term", nil, 3, new(base.Add(72 * time.Hour))},
+		{"stack onto future", new(future), 2, new(future.Add(48 * time.Hour))},
+		{"lapsed term restarts from now", new(past), 1, new(base.Add(24 * time.Hour))},
+		{"zero days unchanged", new(future), 0, new(future)},
+		{"zero days, nil stays nil", nil, 0, nil},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := stackNoAds(tc.current, tc.addDays, base)
+			if (got == nil) != (tc.want == nil) || (got != nil && !got.Equal(*tc.want)) {
+				t.Errorf("stackNoAds = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestCombineNoAds(t *testing.T) {
+	pFuture := base.Add(24 * time.Hour)
+	sFuture := base.Add(72 * time.Hour) // 3 days remaining
+	// primary future + secondary future: primary end + secondary's remaining (72h).
+	if got := combineNoAds(new(pFuture), new(sFuture), base); !got.Equal(pFuture.Add(72 * time.Hour)) {
+		t.Errorf("combine both future = %v, want %v", got, pFuture.Add(72*time.Hour))
+	}
+	// primary nil + secondary future: now + secondary's remaining.
+	if got := combineNoAds(nil, new(sFuture), base); !got.Equal(base.Add(72 * time.Hour)) {
+		t.Errorf("combine nil primary = %v, want %v", got, base.Add(72*time.Hour))
+	}
+	// secondary lapsed: primary unchanged.
+	if got := combineNoAds(new(pFuture), new(base.Add(-time.Hour)), base); !got.Equal(pFuture) {
+		t.Errorf("combine lapsed secondary = %v, want %v", got, pFuture)
+	}
+	// secondary nil: primary unchanged.
+	if got := combineNoAds(new(pFuture), nil, base); !got.Equal(pFuture) {
+		t.Errorf("combine nil secondary = %v, want %v", got, pFuture)
+	}
+}
+
+func TestPlanDraws(t *testing.T) {
+	st := walletState{chips: map[Source]int{SourceDirect: 30, SourceVK: 50, SourceTelegram: 5}}
+	// price met entirely by the first (direct) segment.
+	if draws, ok := planDraws(st, []Source{SourceDirect, SourceVK}, 20); !ok || len(draws) != 1 || draws[0] != (sourceAmount{SourceDirect, 20}) {
+		t.Errorf("single-segment draw = %v ok=%v", draws, ok)
+	}
+	// price spills from direct into vk by priority.
+	draws, ok := planDraws(st, []Source{SourceDirect, SourceVK, SourceTelegram}, 60)
+	want := []sourceAmount{{SourceDirect, 30}, {SourceVK, 30}}
+	if !ok || len(draws) != 2 || draws[0] != want[0] || draws[1] != want[1] {
+		t.Errorf("priority spill draw = %v ok=%v, want %v", draws, ok, want)
+	}
+	// insufficient total.
+	if _, ok := planDraws(st, []Source{SourceDirect, SourceVK, SourceTelegram}, 200); ok {
+		t.Error("expected insufficient")
+	}
+}
+
+func TestWalletSegments(t *testing.T) {
+	id := uuid.New()
+	st := walletState{chips: map[Source]int{SourceDirect: 100, SourceVK: 50}}
+	svc := seededService(id, st)
+	present := []Source{SourceDirect, SourceVK}
+
+	// Web/native: both attached segments shown, both spendable.
+	got, err := svc.Wallet(context.Background(), id, NewContext("direct", "web"), present)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got.Segments) != 2 || !got.Segments[0].Spendable || got.Segments[0].Source != SourceDirect {
+		t.Errorf("direct wallet segments = %+v", got.Segments)
+	}
+	// VK Android: only vk shown, spendable.
+	got, _ = svc.Wallet(context.Background(), id, NewContext("vk", "android"), present)
+	if len(got.Segments) != 1 || got.Segments[0].Source != SourceVK || !got.Segments[0].Spendable {
+		t.Errorf("vk-android wallet = %+v", got.Segments)
+	}
+	// VK iOS: only vk shown, frozen (not spendable) but the balance is visible.
+	got, _ = svc.Wallet(context.Background(), id, NewContext("vk", "ios"), present)
+	if len(got.Segments) != 1 || got.Segments[0].Chips != 50 || got.Segments[0].Spendable {
+		t.Errorf("vk-ios wallet = %+v (want vk 50 frozen)", got.Segments)
+	}
+}
+
+func TestAdFreeByContext(t *testing.T) {
+	id := uuid.New()
+	future := base.Add(48 * time.Hour)
+	ctx := context.Background()
+
+	// A vk-origin no-ads term applies inside VK and out on web, but a direct-origin term never
+	// applies inside VK (the compliance wall).
+	svc := seededService(id, walletState{benefits: map[Source]benefitState{
+		SourceVK:     {adsPaidUntil: new(future)},
+		SourceDirect: {adsPaidUntil: new(future)},
+	}})
+	present := []Source{SourceDirect, SourceVK}
+
+	cases := []struct {
+		name string
+		cxt  Context
+		want bool
+	}{
+		{"vk term inside vk", NewContext("vk", "android"), true},
+		{"vk term inside vk-ios (applies while frozen)", NewContext("vk", "ios"), true},
+		{"terms on web", NewContext("direct", "web"), true},
+		{"untrusted fail-closed", NewContext("", ""), false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := svc.AdFree(ctx, id, tc.cxt, present)
+			if err != nil || got != tc.want {
+				t.Errorf("AdFree = %v (err %v), want %v", got, err, tc.want)
+			}
+		})
+	}
+
+	// Compliance: ONLY a direct-origin term, checked inside VK, must not suppress ads.
+	svc2 := seededService(id, walletState{benefits: map[Source]benefitState{SourceDirect: {adsPaidUntil: new(future)}}})
+	if got, _ := svc2.AdFree(ctx, id, NewContext("vk", "android"), present); got {
+		t.Error("direct-origin no-ads must NOT apply inside VK (compliance wall)")
+	}
+}
+
+func TestHintsAvailableByContext(t *testing.T) {
+	id := uuid.New()
+	svc := seededService(id, walletState{benefits: map[Source]benefitState{
+		SourceDirect: {hints: 3},
+		SourceVK:     {hints: 2},
+	}})
+	present := []Source{SourceDirect, SourceVK}
+	ctx := context.Background()
+
+	// Web: both applicable origins summed.
+	if n, _ := svc.HintsAvailable(ctx, id, NewContext("direct", "web"), present); n != 5 {
+		t.Errorf("web hints = %d, want 5", n)
+	}
+	// VK: only vk-origin hints.
+	if n, _ := svc.HintsAvailable(ctx, id, NewContext("vk", "android"), present); n != 2 {
+		t.Errorf("vk hints = %d, want 2", n)
+	}
+	// Untrusted: none.
+	if n, _ := svc.HintsAvailable(ctx, id, NewContext("", ""), present); n != 0 {
+		t.Errorf("untrusted hints = %d, want 0", n)
+	}
+}
+
+func TestSpendHintUntrustedNoOp(t *testing.T) {
+	id := uuid.New()
+	svc := seededService(id, walletState{benefits: map[Source]benefitState{SourceDirect: {hints: 3}}})
+	// Untrusted context: no applicable origin, so nothing is spent and the DB (nil) is never hit.
+	spent, err := svc.SpendHint(context.Background(), id, NewContext("", ""), []Source{SourceDirect})
+	if err != nil || spent {
+		t.Errorf("untrusted SpendHint = %v (err %v), want false", spent, err)
+	}
+}