fix: FX fallback price broken for peggedREAL (BRTH shows mcap 0)

[0xshubhs]

Fixes #743.

Root cause

BRTH (id 352, peggedREAL, Polygon) has no market price: it isn't on CoinGecko and coins.llama.fi returns {"coins":{}} for it. That part is upstream. But the repo already has an FX-rate fallback for fiat-pegged assets without a market price, and it's broken for BRL pegs in two ways:

1. storeCharts.ts and getChainDominance.ts derive the FX ticker with pegType.slice(-3). For peggedREAL that yields "EAL", but the FX feed (rates/full) keys by ISO code (BRL), so the lookup always misses and the fallback price becomes 0. Every 3-letter pegType (EUR, GBP, JPY, ...) happens to work by accident; peggedREAL is the only 4-letter one and there are 5 such assets.
2. getStableCoins.ts and getStablecoinChains.ts don't use the FX fallback at all — they hardcode pegType === "peggedUSD" ? 1 : 0, so any non-USD asset without a market price gets mcap 0 in the /stablecoins and /stablecoinchains responses even when the chart code path would have priced it.

(BRZ and cREAL never surfaced this because they have CoinGecko prices.)

Change

• src/utils/fxRates.ts: add pegTypeFxTicker() (strips the pegged prefix, with an explicit peggedREAL -> BRL override) and fxFallbackPrice() (1 for USD pegs, 1/fxRate for fiat pegs, 0 for peggedVAR/unknown).
• storeCharts.ts, getChainDominance.ts: use pegTypeFxTicker instead of slice(-3). Also fixed the dominance guard: typeof (1/undefined) === "number" is true for NaN, so the old check never caught a missing rate — now isFinite.
• getStableCoins.ts, getStablecoinChains.ts: replace the hardcoded 0 with fxFallbackPrice fed from the same cron FX cache, so these responses price fiat pegs consistently with the chart/dominance paths.

Test

npm test brth passes (supply adapter reads 2.97k BRTH live from Polygon).

Fallback exercised against the live FX feed:

pegTypeFxTicker(peggedREAL) = BRL
OLD chart lookup (EAL): null
NEW chart lookup (BRL): 5.1451
fxFallbackPrice peggedREAL = 0.1943...   (1/5.1451)
fxFallbackPrice peggedUSD  = 1
fxFallbackPrice peggedVAR  = 0
fxFallbackPrice peggedEUR  = 1.1441...
BRTH mcap with fix ~= $578.61

No new type errors in the touched files (the two pre-existing TS2322s in storeCharts/getChainDominance are unchanged on master).

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📥 Commits

Reviewing files that changed from the base of the PR and between 3803bad and 51bae20.

📒 Files selected for processing (5)

• api2/cron-task/getStableCoins.ts
• api2/cron-task/getStablecoinChains.ts
• api2/cron-task/storeCharts.ts
• api2/routes/getChainDominance.ts
• src/utils/fxRates.ts

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