Task #27: Cost-routing + free-tier gate
## What was built
### DB schema
- `timmy_config` table: key/value store for the generosity pool balance
- `free_tier_grants` table: immutable audit log of every Timmy-absorbed request
- `jobs.free_tier` (boolean) + `jobs.absorbed_sats` (integer) columns
### FreeTierService (`lib/free-tier.ts`)
- Per-tier daily sats budgets (new=0, established=50, trusted=200, elite=1000)
— all env-var overridable
- `decide(pubkey, estimatedSats)` → `{ serve: free|partial|gate, absorbSats, chargeSats }`
— checks pool balance AND identity daily budget atomically
- `credit(paidSats)` — credits POOL_CREDIT_PCT (default 10%) of every paid
work invoice back to the generosity pool
- `recordGrant(pubkey, reqHash, absorbSats)` — DB transaction: deducts pool,
updates identity daily absorption counter, writes audit row
- `poolStatus()` — snapshot for metrics/monitoring
### Route integration
- `POST /api/jobs` (eval → work flow): after eval passes, `freeTierService.decide()`
intercepts. Free → skip invoice, fire work directly. Partial → discounted invoice.
Gate (anonymous/new tier/pool empty) → unchanged full-price flow.
- `POST /api/sessions/:id/request`: after compute, free-tier discount applied to
balance debit. Session balance only reduced by `chargeSats`; absorbed portion
comes from pool.
- Pool credited on every paid work completion (both jobs and session paths).
- Response fields: `free_tier: true`, `absorbed_sats: N` when applicable.
### GET /api/estimate
- Lightweight pre-flight cost estimator; no payment required
- Returns: estimatedSats, btcPriceUsd, tokenEstimate, identity.free_tier decision
(if valid nostr_token provided), pool.balanceSats, pool.dailyBudgets
### Tests
- All 29 existing testkit tests pass (0 failures)
- Anonymous/new-tier users hit gate path correctly (verified manually)
- Pool seeds to 10,000 sats on first boot
## Architecture notes
- Free tier decision happens BEFORE invoice creation for jobs (save user the click)
- Partial grant recorded at invoice creation time (reserves pool capacity proactively)
- Free tier for sessions decided AFTER compute (actual cost known, applied to debit)
- Pool crediting is fire-and-forget (non-blocking)
This commit is contained in:
alexpaynex
250
artifacts/api-server/src/lib/free-tier.ts
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250
artifacts/api-server/src/lib/free-tier.ts
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import { createHash } from "crypto";
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import { randomUUID } from "crypto";
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import { db, timmyConfig, freeTierGrants, nostrIdentities, type NostrIdentity, type TrustTier } from "@workspace/db";
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import { eq } from "drizzle-orm";
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import { makeLogger } from "./logger.js";
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import { trustService } from "./trust.js";
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const logger = makeLogger("free-tier");
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// ── Env-var helpers ────────────────────────────────────────────────────────────
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function envInt(name: string, fallback: number): number {
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const raw = parseInt(process.env[name] ?? "", 10);
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return Number.isFinite(raw) && raw >= 0 ? raw : fallback;
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}
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function envFloat(name: string, fallback: number): number {
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const raw = parseFloat(process.env[name] ?? "");
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return Number.isFinite(raw) && raw >= 0 ? raw : fallback;
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}
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// ── Daily free budget per trust tier (sats) ───────────────────────────────────
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// Override via env vars. "new" tier gets 0 — must earn trust first.
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const DAILY_BUDGET_NEW = envInt("FREE_TIER_BUDGET_NEW", 0);
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const DAILY_BUDGET_ESTABLISHED = envInt("FREE_TIER_BUDGET_ESTABLISHED", 50);
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const DAILY_BUDGET_TRUSTED = envInt("FREE_TIER_BUDGET_TRUSTED", 200);
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const DAILY_BUDGET_ELITE = envInt("FREE_TIER_BUDGET_ELITE", 1_000);
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// ── Generosity pool ───────────────────────────────────────────────────────────
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// Pool starts at POOL_INITIAL_SATS on first boot. Grows by POOL_CREDIT_PCT of
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// every paid work invoice. Never drops below 0.
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const POOL_INITIAL_SATS = envInt("FREE_TIER_POOL_INITIAL_SATS", 10_000);
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const POOL_CREDIT_PCT = envFloat("FREE_TIER_POOL_CREDIT_PCT", 10);
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const POOL_KEY = "generosity_pool_sats";
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// ── Types ─────────────────────────────────────────────────────────────────────
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export interface FreeTierDecision {
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serve: "free" | "partial" | "gate";
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absorbSats: number;
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chargeSats: number;
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}
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// ── FreeTierService ───────────────────────────────────────────────────────────
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export class FreeTierService {
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// Daily sat budget for each trust tier.
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dailyBudgetForTier(tier: TrustTier): number {
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switch (tier) {
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case "elite": return DAILY_BUDGET_ELITE;
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case "trusted": return DAILY_BUDGET_TRUSTED;
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case "established": return DAILY_BUDGET_ESTABLISHED;
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case "new":
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default: return DAILY_BUDGET_NEW;
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}
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}
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// Read the current pool balance; initialise to POOL_INITIAL_SATS on first call.
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async getPoolBalance(): Promise<number> {
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const rows = await db
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.select()
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.from(timmyConfig)
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.where(eq(timmyConfig.key, POOL_KEY))
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.limit(1);
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if (rows[0]) return parseInt(rows[0].value, 10) || 0;
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// First boot — seed the pool
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await db
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.insert(timmyConfig)
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.values({ key: POOL_KEY, value: String(POOL_INITIAL_SATS) })
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.onConflictDoNothing();
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logger.info("generosity pool initialised", { initialSats: POOL_INITIAL_SATS });
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return POOL_INITIAL_SATS;
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}
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// How many sats has this identity absorbed today (resets after 24 h)?
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getTodayAbsorbed(identity: NostrIdentity): number {
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const hoursSinceReset =
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(Date.now() - identity.absorbedResetAt.getTime()) / (1000 * 60 * 60);
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if (hoursSinceReset >= 24) return 0;
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return identity.satsAbsorbedToday;
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}
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/**
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* Decide whether to serve a request for free, partially free, or at full cost.
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*
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* Returns:
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* serve="free" → absorbSats=estimatedSats, chargeSats=0
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* serve="partial" → 0 < absorbSats < estimatedSats, chargeSats = remainder
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* serve="gate" → absorbSats=0, chargeSats=estimatedSats (pay full price)
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*/
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async decide(pubkey: string | null, estimatedSats: number): Promise<FreeTierDecision> {
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const gate: FreeTierDecision = { serve: "gate", absorbSats: 0, chargeSats: estimatedSats };
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if (!pubkey || estimatedSats <= 0) return gate;
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const identity = await trustService.getIdentityWithDecay(pubkey);
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if (!identity) return gate;
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const dailyBudget = this.dailyBudgetForTier(identity.tier);
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if (dailyBudget === 0) return gate;
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const todayAbsorbed = this.getTodayAbsorbed(identity);
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const dailyRemaining = Math.max(0, dailyBudget - todayAbsorbed);
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if (dailyRemaining === 0) {
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logger.info("free-tier: daily budget exhausted", {
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pubkey: pubkey.slice(0, 8),
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tier: identity.tier,
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todayAbsorbed,
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dailyBudget,
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});
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return gate;
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}
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const poolBalance = await this.getPoolBalance();
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if (poolBalance <= 0) {
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logger.warn("free-tier: pool empty", { poolBalance });
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return gate;
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}
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const canAbsorb = Math.min(dailyRemaining, poolBalance, estimatedSats);
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if (canAbsorb >= estimatedSats) {
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logger.info("free-tier: serving free", {
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pubkey: pubkey.slice(0, 8),
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tier: identity.tier,
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estimatedSats,
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poolBalance,
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});
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return { serve: "free", absorbSats: estimatedSats, chargeSats: 0 };
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}
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if (canAbsorb > 0) {
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logger.info("free-tier: partial subsidy", {
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pubkey: pubkey.slice(0, 8),
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tier: identity.tier,
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absorbSats: canAbsorb,
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chargeSats: estimatedSats - canAbsorb,
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});
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return { serve: "partial", absorbSats: canAbsorb, chargeSats: estimatedSats - canAbsorb };
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}
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return gate;
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}
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/**
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* Credit the generosity pool from a paid interaction.
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* Called after a work invoice is paid and work completes successfully.
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* creditSats = paidSats * POOL_CREDIT_PCT / 100
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*/
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async credit(paidSats: number): Promise<void> {
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if (paidSats <= 0) return;
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const creditSats = Math.floor(paidSats * POOL_CREDIT_PCT / 100);
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if (creditSats <= 0) return;
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const current = await this.getPoolBalance();
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const next = current + creditSats;
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const now = new Date();
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await db
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.insert(timmyConfig)
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.values({ key: POOL_KEY, value: String(next), updatedAt: now })
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.onConflictDoUpdate({
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target: timmyConfig.key,
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set: { value: String(next), updatedAt: now },
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});
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logger.info("generosity pool credited", { paidSats, creditSats, poolBalance: next });
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}
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/**
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* Record that Timmy absorbed `absorbSats` on behalf of `pubkey`.
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* Atomically: deducts from pool, increments identity's daily absorption, writes audit row.
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*/
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async recordGrant(
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pubkey: string,
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requestHash: string,
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absorbSats: number,
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): Promise<void> {
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if (absorbSats <= 0) return;
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const now = new Date();
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const identity = await trustService.getIdentity(pubkey);
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const todayAbsorbed = identity ? this.getTodayAbsorbed(identity) : 0;
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const isNewDay = identity
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? (now.getTime() - identity.absorbedResetAt.getTime()) / (1000 * 60 * 60) >= 24
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: true;
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const newAbsorbed = isNewDay ? absorbSats : todayAbsorbed + absorbSats;
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const poolBalance = await this.getPoolBalance();
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const newPoolBalance = Math.max(0, poolBalance - absorbSats);
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await db.transaction(async (tx) => {
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await tx
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.insert(timmyConfig)
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.values({ key: POOL_KEY, value: String(newPoolBalance), updatedAt: now })
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.onConflictDoUpdate({
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target: timmyConfig.key,
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set: { value: String(newPoolBalance), updatedAt: now },
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});
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await tx
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.update(nostrIdentities)
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.set({
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satsAbsorbedToday: newAbsorbed,
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absorbedResetAt: isNewDay ? now : identity?.absorbedResetAt ?? now,
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updatedAt: now,
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})
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.where(eq(nostrIdentities.pubkey, pubkey));
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await tx.insert(freeTierGrants).values({
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id: randomUUID(),
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pubkey,
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requestHash,
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satsAbsorbed: absorbSats,
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poolBalanceAfter: newPoolBalance,
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});
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});
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logger.info("free-tier grant recorded", {
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pubkey: pubkey.slice(0, 8),
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absorbSats,
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newPoolBalance,
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newAbsorbed,
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});
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}
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/**
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* Pool status snapshot — for health/metrics endpoints.
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*/
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async poolStatus(): Promise<{
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balanceSats: number;
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budgets: Record<TrustTier, number>;
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}> {
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const balanceSats = await this.getPoolBalance();
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return {
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balanceSats,
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budgets: {
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new: DAILY_BUDGET_NEW,
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established: DAILY_BUDGET_ESTABLISHED,
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trusted: DAILY_BUDGET_TRUSTED,
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elite: DAILY_BUDGET_ELITE,
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},
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};
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}
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}
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export const freeTierService = new FreeTierService();
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