Fix struct field name normalization for gas estimation auto-fill

Dedot's SCALE codec normalizes struct field names to camelCase via
stringCamelCase (ref_time → refTime, proof_size → proofSize). Our
codec and auto-fill code was using raw metadata names (snake_case),
causing 'Cannot mix BigInt and other types' encoding errors in the
Information Pane after gas estimation.

Fix at the shared layer:
- Add normalizeFieldName() to lib/codec.ts matching Dedot's convention
- Use it in decomposeArgHex for struct and enum field value lookups
- Simplify gas estimation auto-fill to use camelCase directly

Author: itsyogesh

components/builder/extrinsic-builder.tsx

@@ -110,29 +110,11 @@ const ExtrinsicBuilder: React.FC<ExtrinsicBuilderProps> = ({
   useEffect(() => {
     if (!isReviveInstantiate || !gasEstimation.weightRequired || !tx) return;
 
-    // Resolve weight field names from metadata
-    const weightField = tx.meta?.fields?.find((f) => f.name === "weight_limit");
-    if (weightField) {
-      try {
-        const weightType = client.registry.findType(weightField.typeId);
-        const { typeDef } = weightType;
-        if (typeDef.type === "Struct" && typeDef.value.fields.length >= 2) {
-          const [field0, field1] = typeDef.value.fields;
-          const name0 = String(field0.name);
-          const name1 = String(field1.name);
-          builderForm.setValue("weight_limit", {
-            [name0]: String(gasEstimation.weightRequired.refTime),
-            [name1]: String(gasEstimation.weightRequired.proofSize),
-          });
-        }
-      } catch {
-        // Fallback: use camelCase names
-        builderForm.setValue("weight_limit", {
-          refTime: String(gasEstimation.weightRequired.refTime),
-          proofSize: String(gasEstimation.weightRequired.proofSize),
-        });
-      }
-    }
+    // Auto-fill weight_limit with camelCase keys (Dedot codec convention)
+    builderForm.setValue("weight_limit", {
+      refTime: String(gasEstimation.weightRequired.refTime),
+      proofSize: String(gasEstimation.weightRequired.proofSize),
+    });
 
     // Auto-fill storage deposit only for Charge
     if (gasEstimation.storageDeposit?.type === "Charge") {

lib/codec.ts

@@ -1,5 +1,13 @@
 import { DedotClient } from "dedot";
-import { u8aToHex, hexToU8a, hexStripPrefix, hexAddPrefix, decodeAddress } from "dedot/utils";
+import { u8aToHex, hexToU8a, hexStripPrefix, hexAddPrefix, decodeAddress, stringCamelCase } from "dedot/utils";
+
+/**
+ * Normalize a metadata field name to camelCase, matching Dedot's internal convention.
+ * Metadata uses snake_case (ref_time, proof_size), but Dedot codecs expect camelCase.
+ */
+export function normalizeFieldName(name: string): string {
+  return stringCamelCase(name.replace("#", "_"));
+}
 
 /**
  * Result type for encoding operations
@@ -541,7 +549,7 @@ export function decomposeArgHex(
       if (fields.length > 0 && typeof value === "object" && value !== null && !Array.isArray(value)) {
         const obj = value as Record<string, unknown>;
         const children: HexChildItem[] = fields.map((field) => {
-          const fieldName = field.name || "";
+          const fieldName = normalizeFieldName(field.name || "");
           const fieldValue = obj[fieldName];
           const result = encodeArg(client, field.typeId, fieldValue);
           return {
@@ -577,7 +585,7 @@ export function decomposeArgHex(
           if (typeof enumObj.value === "object" && enumObj.value !== null) {
             const obj = enumObj.value as Record<string, unknown>;
             const children: HexChildItem[] = variant.fields.map((field) => {
-              const fieldName = field.name || "";
+              const fieldName = normalizeFieldName(field.name || "");
               const fieldValue = obj[fieldName];
               const result = encodeArg(client, field.typeId, fieldValue);
               return {