feat(executor): EIP-1559 gas oracle + concurrent nonce manager

config/default.toml

@@ -28,9 +28,11 @@ signer_key = "${CHARON_SIGNER_KEY:-}"
 
 # ── Chains ────────────────────────────────────────────────────────────────
 [chain.bnb]
-chain_id  = 56
-ws_url    = "${BNB_WS_URL}"
-http_url  = "${BNB_HTTP_URL}"
+chain_id           = 56
+ws_url             = "${BNB_WS_URL}"
+http_url           = "${BNB_HTTP_URL}"
+# Validator-friendly tip on BSC; raise during congestion.
+priority_fee_gwei  = 1
 
 # ── Lending protocols ─────────────────────────────────────────────────────
 [protocol.venus]

crates/charon-core/src/config.rs

@@ -186,12 +186,25 @@ fn default_cold_scan_blocks() -> u64 {
 
 /// RPC endpoints for a single chain. **The URLs typically embed API keys;
 /// `Debug` prints `<redacted>` rather than the URL.**
+///
+/// `priority_fee_gwei` is the EIP-1559 priority fee (tip) the gas
+/// oracle attaches per chain, expressed in gwei for operator
+/// readability. Defaults to `1` — BSC validators are fine with a
+/// 1 gwei tip; L2s running sub-gwei tips should override explicitly.
+/// The oracle converts to wei internally; mixing units silently
+/// under-filters at 1e9×.
 #[derive(Clone, Deserialize)]
 #[serde(deny_unknown_fields)]
 pub struct ChainConfig {
     pub chain_id: u64,
     pub ws_url: String,
     pub http_url: String,
+    #[serde(default = "default_priority_fee_gwei")]
+    pub priority_fee_gwei: u64,
+}
+
+fn default_priority_fee_gwei() -> u64 {
+    1
 }
 
 impl fmt::Debug for ChainConfig {
@@ -200,6 +213,7 @@ impl fmt::Debug for ChainConfig {
             .field("chain_id", &self.chain_id)
             .field("ws_url", &"<redacted>")
             .field("http_url", &"<redacted>")
+            .field("priority_fee_gwei", &self.priority_fee_gwei)
             .finish()
     }
 }