fix(assets-controller): add partialSupport from AccountsAPI

packages/assets-controller/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- `AccountsApiDataSource` now treats Accounts API `/v2/supportedNetworks` `partialSupport.balances` as active chains in addition to `fullSupport`, still gated by the Snaps assets migration feature flags ([#10144](https://github.com/MetaMask/core/pull/10144))
+
 ## [15.1.0]
 
 ### Changed

packages/assets-controller/src/data-sources/AccountsApiDataSource.ts

@@ -124,6 +124,39 @@ function decimalToChainId(decimalChainId: number | string): ChainId {
   return toCaipChainId(KnownCaipNamespace.Eip155, String(decimalChainId));
 }
 
+/**
+ * Collect chain ids from Accounts API `/v2/supportedNetworks`.
+ *
+ * `fullSupport` is the primary list. `partialSupport.balances` is included so
+ * networks that are not yet promoted to full support (e.g. Tron) can still be
+ * claimed by this data source on current clients. A raw array `partialSupport`
+ * (legacy / unused v2 mock shape) is ignored — only `{ balances }` is read.
+ *
+ * @param response - The v2 supported-networks payload.
+ * @param response.fullSupport - Fully supported chain ids (decimals or CAIP-2).
+ * @param response.partialSupport - Partial support object or legacy array; only `{ balances }` is read.
+ * @returns Unique normalized chain ids, `fullSupport` first then `partialSupport.balances`.
+ */
+function collectSupportedNetworkIds(response: {
+  fullSupport?: (number | string)[];
+  partialSupport?: { balances?: (number | string)[] } | (number | string)[];
+}): ChainId[] {
+  const fullSupport = response.fullSupport ?? [];
+  const { partialSupport } = response;
+  const partialBalances =
+    partialSupport && !Array.isArray(partialSupport)
+      ? (partialSupport.balances ?? [])
+      : [];
+
+  return [
+    ...new Set(
+      [...fullSupport, ...partialBalances].map((rawChainId) =>
+        decimalToChainId(rawChainId),
+      ),
+    ),
+  ];
+}
+
 /**
  * Convert a CAIP-2 chain ID from the API response to our ChainId type.
  * Handles both formats: "eip155:1" or just "1" (decimal).
@@ -367,17 +400,17 @@ export class AccountsApiDataSource extends AbstractDataSource<
   async #fetchActiveChains(): Promise<ChainId[]> {
     const response = await this.#apiClient.accounts.fetchV2SupportedNetworks();
 
-    // Use fullSupport networks as active chains, gated by the Snaps →
-    // AssetsController migration FF: non-migration namespaces (e.g. `eip155`)
-    // are always surfaced, while migration networks (Solana, Stellar, Tron) are
-    // only surfaced once their per-network stage reaches
+    // Use fullSupport and partialSupport.balances as active chains, gated by
+    // the Snaps → AssetsController migration FF: non-migration namespaces
+    // (e.g. `eip155`) are always surfaced, while migration networks (Solana,
+    // Stellar, Tron) are only surfaced once their per-network stage reaches
     // ReadAssetsControllerWithFallback.
     const { remoteFeatureFlags } = this.#messenger.call(
       'RemoteFeatureFlagController:getState',
     );
-    return response.fullSupport
-      .map(decimalToChainId)
-      .filter((chainId) => shouldSupportChain(chainId, remoteFeatureFlags));
+    return collectSupportedNetworkIds(response).filter((chainId) =>
+      shouldSupportChain(chainId, remoteFeatureFlags),
+    );
   }
 
   // ============================================================================