feat(core): add TOML config loader with ${ENV_VAR} substitution

.env.example

@@ -0,0 +1,8 @@
+# Charon environment variables.
+# Copy to `.env` and fill in real values. `.env` is git-ignored.
+
+# BNB Chain RPC endpoints.
+# Public defaults work for testing but are rate-limited; swap in a private
+# endpoint (QuickNode / Ankr / Blast / your own node) for production use.
+BNB_WS_URL=wss://bsc-rpc.publicnode.com
+BNB_HTTP_URL=https://bsc-rpc.publicnode.com

config/default.toml

@@ -0,0 +1,36 @@
+# Charon — v1 config (Venus on BNB Chain)
+#
+# Secrets (RPC URLs) are referenced via ${ENV_VAR} and substituted from
+# the environment at load time. See `.env.example` for the expected vars.
+
+[bot]
+# Drop opportunities below this USD profit threshold, in USD × 1e6.
+# 5_000_000 = $5.00. Integer fixed-point to avoid f64 precision.
+min_profit_usd_1e6 = 5000000
+# Skip liquidations when gas price exceeds this, in wei (decimal string).
+# "3000000000" = 3 gwei. Sub-gwei priority fees are representable.
+max_gas_wei = "3000000000"
+# Polling cadence for protocols without push events (ms).
+scan_interval_ms = 1000
+
+# ── Chains ────────────────────────────────────────────────────────────────
+[chain.bnb]
+chain_id  = 56
+ws_url    = "${BNB_WS_URL}"
+http_url  = "${BNB_HTTP_URL}"
+
+# ── Lending protocols ─────────────────────────────────────────────────────
+[protocol.venus]
+chain       = "bnb"
+# Venus Unitroller (main comptroller on BSC)
+comptroller = "0xfd36e2c2a6789db23113685031d7f16329158384"
+
+# ── Flash-loan sources ────────────────────────────────────────────────────
+[flashloan.aave_v3_bsc]
+chain = "bnb"
+# Aave V3 Pool on BSC (used for flashLoanSimple — 0.05% fee)
+pool  = "0x6807dc923806fe8fd134338eabca509979a7e0cb"
+
+# ── Deployed liquidator contracts ─────────────────────────────────────────
+# Populated once CharonLiquidator.sol is deployed on BSC mainnet. Do not
+# add a zero-address placeholder — config validation rejects it.

crates/charon-core/Cargo.toml

@@ -13,4 +13,5 @@ alloy = { workspace = true }
 serde = { workspace = true }
 anyhow = { workspace = true }
 async-trait = { workspace = true }
+toml = { workspace = true }
 thiserror = { workspace = true }