fix(liquidity): preselect highest LP holding

apps/amm/client/src/api/quote.rs

@@ -462,12 +462,21 @@ fn compute_active_quote(
     let lp_options = holding_options(&holdings, pair.lp_definition);
     let lp_holding = if input.request.create_fresh_lp {
         None
-    } else {
+    } else if input.request.lp_holding_id.is_some() {
         select_holding(
             &holdings,
             pair.lp_definition,
             input.request.lp_holding_id.as_deref(),
         )
+    } else {
+        lp_options
+            .iter()
+            .max_by(|left, right| {
+                left.balance
+                    .cmp(&right.balance)
+                    .then_with(|| right.id.cmp(&left.id))
+            })
+            .cloned()
     };
     let lp_destination_selected =
         input.request.create_fresh_lp || lp_holding.is_some() || lp_options.is_empty();

apps/amm/client/src/api/tests.rs

@@ -717,22 +717,38 @@ fn active_pool_quote_uses_ratio_and_existing_lp_holding() {
         ),
     ];
     let lp_holding = AccountId::new([64; 32]);
+    let highest_lp_holding = AccountId::new([65; 32]);
     scenario.snapshot.wallet_accounts.push(account_read(
         lp_holding,
         &token_holding(pair.lp_definition, 500),
     ));
+    scenario.snapshot.wallet_accounts.push(account_read(
+        highest_lp_holding,
+        &token_holding(pair.lp_definition, 750),
+    ));
     scenario.request.initial_price_real_raw = None;
     scenario.request.max_amount_a_raw = Some(String::from("1000"));
     scenario.request.max_amount_b_raw = Some(String::from("3000"));
     scenario.request.slippage_bps = Some(50);
 
-    let awaiting_destination = scenario.quote();
-    assert_eq!(awaiting_destination["lpDestinationRequired"], true);
-    assert_eq!(awaiting_destination["canSubmit"], false);
+    let default_destination = scenario.quote();
+    assert_eq!(default_destination["lpDestinationRequired"], false);
     assert_eq!(
-        awaiting_destination["errors"][0]["code"],
+        default_destination["selectedLpHoldingId"],
+        highest_lp_holding.to_string()
+    );
+    assert_eq!(default_destination["canSubmit"], true);
+    assert_eq!(default_destination["errors"], json!([]));
+
+    scenario.request.lp_holding_id = Some(AccountId::new([66; 32]).to_string());
+    let invalid_destination = scenario.quote();
+    assert_eq!(invalid_destination["lpDestinationRequired"], true);
+    assert_eq!(invalid_destination["canSubmit"], false);
+    assert_eq!(
+        invalid_destination["errors"][0]["code"],
         "lp_destination_required"
     );
+
     scenario.request.lp_holding_id = Some(lp_holding.to_string());
 
     let quote_value = scenario.quote();
@@ -742,6 +758,7 @@ fn active_pool_quote_uses_ratio_and_existing_lp_holding() {
     assert_eq!(quote_value["expectedLpRaw"], "1000");
     assert_eq!(quote_value["minimumLpRaw"], "995");
     assert_eq!(quote_value["requiresFreshLp"], false);
+    assert_eq!(quote_value["selectedLpHoldingId"], lp_holding.to_string());
     assert_eq!(quote_value["canSubmit"], true);
     assert_eq!(quote_value["errors"], json!([]));