Add rate field to GetQuoteResponse

.claude/rules/fee-and-quotes.md

@@ -4,6 +4,9 @@ globs: csharp/**
 
 # Fee & Quote System
 
+## Rate Field on GetQuoteResponse
+`GetQuoteResponse.rate` (proto `string`, domain `QuoteWithSolverDto.Rate` as `decimal`) is the **gross, pre-fee** exchange rate returned by `IRateProvider.GetRateAsync(route)` — matches Layerswap semantics (`SwapQuoteModel.Rate` populated from the product of per-hop `route.Rate` values in `ViewModelMapper.MapQuoteResponseAsync`, where each `route.Rate` is the raw provider rate). For `SameAssetRateProvider` this is `1m`; for `TokenPriceRateProvider` it is `srcPriceUsd / dstPriceUsd`. Purely informational — the solver's fee and receive-amount math already uses this value internally; it's just surfaced now. Mapped to proto as invariant-culture `"G"` in `SolverProtoMapper.ToGetQuoteResponse`.
+
 ## Quote Fee Calculation
 `QuoteService` (in `Infrastructure/Quote/QuoteService.cs`) computes total fees for a quote:
 

csharp/src/Infrastructure/Quote/QuoteService.cs

@@ -210,6 +210,7 @@ await CalculateTotalFeeAsync(route, amount, rewardAmountInDestNative: rewardAmou
         {
             Amount = amount,
             ReceiveAmount = receiveAmount,
+            Rate = swapRate,
             TotalFee = totalFee,
             TotalServiceFee = totalServiceFee,
             TotalExpenseFee = totalExpenseFee,

csharp/src/Shared.Models/Models/QuoteWithSolverDto.cs

@@ -13,6 +13,8 @@ public class QuoteWithSolverDto : QuoteDto
 
     public BigInteger Amount { get; set; }
 
+    public decimal Rate { get; set; }
+
     public BigInteger RewardAmount { get; set; }
 
     public string Signature { get; set; } = string.Empty;

csharp/src/Shared.Proto/SolverProtoMapper.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using Google.Protobuf.WellKnownTypes;
 using Train.Solver.Shared.Models.Events;
 using DomainModels = Train.Solver.Shared.Models;
@@ -53,6 +54,7 @@ public static class SolverProtoMapper
         TotalExpenseFee = quote.TotalExpenseFee.ToString(),
         TotalRewardFee = quote.TotalRewardFee.ToString(),
         Amount = quote.Amount.ToString(),
+        Rate = quote.Rate.ToString("G", CultureInfo.InvariantCulture),
     };
 
     #endregion

protos/solver.proto

@@ -69,6 +69,7 @@ message GetQuoteResponse {
   string total_expense_fee = 11;     // BigInteger as string (source token units)
   string total_reward_fee = 12;      // BigInteger as string (source token units)
   string amount = 13;                // BigInteger as string (source amount — useful for reverse quotes)
+  string rate = 14;                  // Gross pre-fee exchange rate from IRateProvider (decimal): destination per 1 source token
 }
 
 message RewardInfo {