fix(forex): replace CurrencyFreaks with ECB

- Fetch GBP/USD through Frankfurter with a seven-day backward-only fallback and strict validation
- Preserve saved observations and backfill August 26–31, 2026
- Fail incomplete fetches and remove the unused cron API key dependency

Agent-Session: codex/01a080b3-6571-7580-9a47-1d7202ec529f

Author: PaulRBerg

.github/workflows/cron-update-data.yml

@@ -25,9 +25,7 @@ jobs:
           COINGECKO_API_KEY: ${{ secrets.COINGECKO_API_KEY }}
         run: just fetch-crypto-recent --currency all
 
-      - name: Fetch forex rates
-        env:
-          CURRENCY_FREAKS_API_KEY: ${{ secrets.CURRENCY_FREAKS_API_KEY }}
+      - name: Fetch ECB forex rates
         run: just fetch-forex
 
       - name: Validate TSV files

AGENTS.md

@@ -6,7 +6,7 @@ This document contains instructions for AI agents working on the Sablier Price D
 
 This repo provides centralized cryptocurrency and forex exchange rate data used across Sablier projects. The data is
 stored in TSV format and sourced from [CoinGecko](https://coingecko.com/api) (crypto prices) and
-[CurrencyFreaks](https://currencyfreaks.com/) (forex rates).
+[Frankfurter](https://frankfurter.dev/) with `providers=ECB` (forex rates; no API key required).
 
 ## Development
 
@@ -18,7 +18,7 @@ stored in TSV format and sourced from [CoinGecko](https://coingecko.com/api) (cr
 - `just tsv-check` - Validate TSV files against schema
 - `ni <package>` - Install dependency (`ni -D` for dev dependency)
 - `just fetch-crypto --currency <symbol>` - Fetch crypto prices from CoinGecko
-- `just fetch-forex` - Fetch GBP/USD rates from CurrencyFreaks
+- `just fetch-forex` - Append missing GBP/USD rates from Frankfurter (ECB)
 
 ## TSV Format
 
@@ -28,3 +28,13 @@ stored in TSV format and sourced from [CoinGecko](https://coingecko.com/api) (cr
 - **Price format**: Decimal number (high precision), no quotes
 - **Structure**: `id` (date) and `output` (price) columns
 - **Validation**: Use `just tsv-check` to validate TSV files
+
+## Forex provider policy
+
+`fetch-forex` preserves existing observations and fills missing dates only. CurrencyFreaks observations through
+2026-08-25 remain unchanged; new observations use ECB via Frankfurter v2. GBP is the base, USD is the quote.
+Weekend/holiday dates use the nearest earlier ECB observation, at most seven days before the requested date. Never use a
+future observation, change provider implicitly, or turn an API failure into a successful partial month. Only HTTP 404
+triggers backward lookup; other errors fail the command. Current-month runs stop at yesterday in UTC.
+
+Run provider tests with `node --import tsx --test src/cli/fetch-forex/frankfurter-client.test.ts`.

README.md

@@ -18,7 +18,13 @@ By centralizing the data here, we avoid duplication and ensure consistency acros
 All price data is sourced from industry-standard APIs:
 
 - **Cryptocurrency Prices**: [CoinGecko API](https://coingecko.com/api) - Daily historical prices in USD
-- **Forex Exchange Rates**: [CurrencyFreaks API](https://currencyfreaks.com/) - Daily GBP/USD exchange rates
+- **Forex Exchange Rates**: [Frankfurter API](https://frankfurter.dev/) - ECB GBP/USD reference rates, no API key
+  required
+
+Forex observations through August 25, 2026 retain their original CurrencyFreaks values. From August 26, missing dates
+are filled from Frankfurter v2 with the provider pinned to ECB. Weekend and holiday dates carry the nearest earlier ECB
+observation, up to seven days back. Fetches preserve saved observations and fail if a requested date cannot be resolved.
+Run `just fetch-forex --year 2026 --month 08` to fill a specific month.
 
 ## Data Structure
 
@@ -47,7 +53,7 @@ We use this data structure to make it easier to use the files in our
 - Dates are in UTC timezone
 - Dates are sorted chronologically
 - No duplicate dates within a file
-- Prices are daily closing prices (00:00 UTC)
+- Crypto prices use daily closing observations; forex uses ECB reference rates with the fallback policy above
 
 ## Installation
 

forex/GBP_USD.tsv

@@ -1695,4 +1695,10 @@ id	output
 "2026-08-22"	1.3634
 "2026-08-23"	1.3653
 "2026-08-24"	1.3638
-"2026-08-25"	1.3647
+"2026-08-25"	1.3647
+"2026-08-26"	1.363
+"2026-08-27"	1.3582
+"2026-08-28"	1.3583
+"2026-08-29"	1.3583
+"2026-08-30"	1.3583
+"2026-08-31"	1.3539

justfile

@@ -48,7 +48,7 @@ YEAR := ```
         --currency {{ currency }} \
         --recent-days {{ days }}
 
-# Fetch daily GBP/USD forex rates from CurrencyFreaks
+# Fetch daily GBP/USD forex rates from Frankfurter (ECB)
 [arg("year", long)]
 [arg("month", long)]
 @fetch-forex year=YEAR month="all" *args:

src/cli/fetch-forex.ts

@@ -9,7 +9,7 @@ import dayjs from "dayjs";
 import utc from "dayjs/plugin/utc.js";
 import ora from "ora";
 import { toFloat } from "radash";
-import { fetchDailyForexRates } from "./fetch-forex/currencyfreaks-client.js";
+import { fetchDailyForexRates } from "./fetch-forex/frankfurter-client.js";
 import { getForexTsvPath, updateTsvFile } from "./fetch-forex/tsv-utils.js";
 
 dayjs.extend(utc);
@@ -257,7 +257,7 @@ async function fetchForexRatesAction(options: FetchForexRatesOptions): Promise<v
       const spinner = ora(`Fetching ${yearStr}-${monthStr}`).start();
 
       try {
-        // Fetch daily rates from CurrencyFreaks API
+        // Fetch daily rates from Frankfurter API (ECB)
         const forexRates = await fetchDailyForexRates(year, month);
 
         // Update TSV file with new data
@@ -299,6 +299,9 @@ async function fetchForexRatesAction(options: FetchForexRatesOptions): Promise<v
 
     // Display summary table
     displaySummaryTable(results);
+    if (results.some((result) => result.status === "error")) {
+      throw new Error("One or more forex months failed to fetch");
+    }
     return;
   }
 
@@ -317,7 +320,7 @@ async function fetchForexRatesAction(options: FetchForexRatesOptions): Promise<v
   const spinner = ora(`Fetching GBP/USD forex rates for ${year}-${month}`).start();
 
   try {
-    // Fetch daily rates from CurrencyFreaks API
+    // Fetch daily rates from Frankfurter API (ECB)
     const forexRates = await fetchDailyForexRates(yearNum, monthNum);
 
     if (forexRates.length === 0) {
@@ -353,7 +356,7 @@ function createFetchForexRatesCommand(): Command {
   const command = new Command();
 
   command
-    .description("Fetch daily GBP/USD forex rates from CurrencyFreaks API")
+    .description("Fetch daily GBP/USD forex rates from Frankfurter API (ECB)")
     .option("--year <YYYY>", "Year in YYYY format (defaults to current year)")
     .option(
       "--month <MM>",