docs(fee): correct ADR historical example and add kRate=10000 case

Drop the mistaken Arc-curve attribution for early-testnet's 7 wei floor
(that era was EIP-1559), clarify committed vs live fee params, note the
EIP-1559-equivalence of the 1250/5000 test vector, and cover the
ProtocolConfig max kRate=10000 empty-block-to-zero boundary.

Author: kutluhaneth46

crates/execution-config/src/gas_fee.rs

@@ -390,8 +390,11 @@ mod tests {
 
     /// Empty blocks stop lowering the fee once `base_fee * k_rate < 10_000`
     /// (integer truncation on the decrease path). At production-scale gas
-    /// limits the resting value is `ceil(10000/k_rate) - 1` — matching early
-    /// testnet (`k_rate = 1250` → 7 wei) from #367.
+    /// limits the resting value is `ceil(10000/k_rate) - 1`.
+    ///
+    /// `k_rate = 1250` / `iem = 5000` is the EIP-1559 equivalence point
+    /// (`10000/8`, `10000/2`) already exercised by `test_calc_next_block_base_fee`
+    /// — not a historical Arc testnet parameter set (see #367 / #372).
     #[test]
     fn empty_blocks_rest_at_truncation_floor() {
         let k_rate = 1250;
@@ -421,5 +424,17 @@ mod tests {
             base_fee, resting,
             "long empty-block run reaches resting value"
         );
+
+        // Max ProtocolConfig kRate: decrease == base_fee, so one empty block
+        // reaches 0 (resting = ceil(10000/10000) - 1 = 0) before output clamps.
+        assert_eq!(
+            arc_calc_next_block_base_fee(0, gas_limit, 42, 10_000, iem),
+            0,
+            "kRate=10000 empties the fee in one step"
+        );
+        assert_eq!(
+            arc_calc_next_block_base_fee(0, gas_limit, 0, 10_000, iem),
+            0
+        );
     }
 }

docs/adr/0004-base-fee-validation.md

@@ -132,7 +132,6 @@ next_base_fee = arc_calc_next_block_base_fee(smoothed_gas, gas_limit, base_fee,
 if fee_params is not None:
     next_base_fee = clamp(next_base_fee, fee_params.minBaseFee, fee_params.maxBaseFee)
 
-
 # 4. Apply chainspec absolute bounds
 next_base_fee = clamp(next_base_fee, config.absolute_min_base_fee, config.absolute_max_base_fee)
 
@@ -172,9 +171,11 @@ resting_value = ceil(10000 / kRate) - 1
 effective_floor ≈ max(minBaseFee, resting_value)
 ```
 
-`10000 / kRate` is the truncation *threshold*; the fee comes to rest one wei below it (e.g. `kRate = 1250` ⇒ threshold 8, rest 7; `kRate = 200` ⇒ threshold 50, rest 49). Operators reading only `feeParams.minBaseFee` can miss this interaction. It does not affect mainnet as currently configured (`minBaseFee = 20 gwei`, `kRate = 200`), but early testnet sat at 7 wei for millions of blocks against a declared `minBaseFee` of 1. A future governance update that lowers `minBaseFee` below that resting value (or lowers `kRate` enough to raise it above `minBaseFee`) would recreate the gap. See #367.
+`10000 / kRate` is the truncation *threshold*; the fee comes to rest one wei below it (e.g. `kRate = 1250` ⇒ threshold 8, rest 7; `kRate = 200` ⇒ threshold 50, rest 49; `kRate = 10000` ⇒ rest 0, so a single empty block reaches zero before the output clamp). Operators reading only `feeParams.minBaseFee` can miss this interaction.
+
+This is a **forward-looking governance risk**, not a past Arc-curve incident: since the Arc fee curve has been live on testnet (`kRate = 200` from block ~21,659,090), `minBaseFee` has stayed well above the resting value (49 wei). The 7 wei floor observed earlier on testnet came from plain EIP-1559 dynamics (`/8`), not from Arc `kRate` truncation — do not treat that history as evidence the Arc curve already gapped. A future `updateFeeParams` that lowers `minBaseFee` below `ceil(10000/kRate) - 1` (or raises that resting value above `minBaseFee`) would create the gap. See #367.
 
-Also note: the fee parameters in `assets/testnet/config.json` are **historical genesis values**. Live testnet `ProtocolConfig.feeParams()` currently matches the mainnet parameter set.
+Also note: `assets/testnet/config.json` / `assets/devnet/config.json` fee params (`kRate: 25`, `minBaseFee: 1`) are **historical genesis values** (predicted Arc resting value 399). Live testnet `ProtocolConfig.feeParams()` currently matches the mainnet-like set (`kRate: 200`).
 
 ## Consequences