derive NameRegistration JSON the same way on every build

sumTypeJSON switches to the _owsf form on swift builds, but this JSON is
  the RNAME payload and the resolver's HTTP contract, so a swift client and
  a Linux relay would disagree on every field. taggedObjectJSON is what it
  already resolves to everywhere else.

  The label modifier keeps the reservedReason_ collision escape out of the
  API, as AgentWorkersDetails does: both arms now say reservedReason.

protocol/simplex-messaging.md

@@ -1549,7 +1549,7 @@ seconds since the Unix epoch. Lengths are characters.
 |---|---|---|---|
 | `expires` | `registered` | number | absent only from a v20/v21 router, which sent the record alone |
 | `graceUntil` | `registered` | number | after `expires`; until here only the owner may renew. Absent on the same condition as `expires` |
-| `reservedReason_` | `registered` | string | a reason word, present only when the name is held back as well |
+| `reservedReason` | `registered` | string | a reason word, present only when the name is held back as well |
 | `nameRecord` | `registered` | object | the record, schema below |
 | `pricing` | `available` | object | `registrationPrices`, `basePrice` and `minLabelLength`, below |
 | `reservedReason` | `reserved` | string | a reason word |
@@ -1566,7 +1566,7 @@ JSON and in a client's own API.
 
 `available` alone means registrable: a name the registry holds back answers
 `reserved` instead, so a client has no flags to combine. A reservation on a name
-that *is* registered is carried in `reservedReason_`, and is why that name will
+that *is* registered is carried in `reservedReason`, and is why that name will
 not free up when it expires.
 
 There is no separate answer for an auction. A name past its grace period answers

scripts/resolver/service/snrc-resolve.py

@@ -744,7 +744,7 @@ def registration(name: str):
             "type": "registered",
             "expires": reg["expires"],
             "graceUntil": reg["graceEnds"],
-            "reservedReason_": reg["reasonCode"],
+            "reservedReason": reg["reasonCode"],
             "nameRecord": name_record(name),
         }
     if reg["reasonCode"]:

src/Simplex/Messaging/Names/Record.hs

@@ -23,7 +23,7 @@ import Data.Int (Int64)
 import Data.Map.Strict (Map)
 import Data.Text (Text)
 import Simplex.Messaging.Encoding.String
-import Simplex.Messaging.Parsers (defaultJSON, dropPrefix, sumTypeJSON)
+import Simplex.Messaging.Parsers (defaultJSON, dropPrefix, taggedObjectJSON)
 import Simplex.Messaging.SystemTime (SystemSeconds)
 
 -- | Resolved name record returned by the names role. JSON keys match the
@@ -132,4 +132,10 @@ oldRegistration nameRecord =
 
 $(JQ.deriveJSON defaultJSON ''NamePricing)
 
-$(JQ.deriveJSON (sumTypeJSON $ dropPrefix "NR") ''NameRegistration)
+-- taggedObjectJSON, not sumTypeJSON: this JSON is the RNAME payload and the
+-- resolver contract, so it must not vary with the swift build flag. The label
+-- modifier keeps the reservedReason_ collision escape out of the API.
+$( JQ.deriveJSON
+    (taggedObjectJSON $ dropPrefix "NR") {J.fieldLabelModifier = takeWhile (/= '_')}
+    ''NameRegistration
+ )

tests/SMPNamesTests.hs

@@ -54,7 +54,7 @@ testNameRecord =
 -- from the Haskell value: the literal JSON is the contract with the resolver.
 registeredBody :: NameRecord -> LB.ByteString
 registeredBody nameRec =
-  "{\"type\":\"registered\",\"expires\":1813853483,\"graceUntil\":1821629483,\"reservedReason_\":null,\"nameRecord\":" <> J.encode nameRec <> "}"
+  "{\"type\":\"registered\",\"expires\":1813853483,\"graceUntil\":1821629483,\"reservedReason\":null,\"nameRecord\":" <> J.encode nameRec <> "}"
 
 availableBody :: LB.ByteString
 availableBody = "{\"type\":\"available\",\"pricing\":{\"registrationPrices\":{\"3\":12793,\"4\":3198},\"basePrice\":100,\"minLabelLength\":3}}"
@@ -177,7 +177,7 @@ availabilitySpec = do
     J.encode NRRTrademark `shouldBe` "\"trademark\""
   where
     heldBackBody =
-      "{\"type\":\"registered\",\"expires\":1813853483,\"graceUntil\":1821629483,\"reservedReason_\":\"internal\",\"nameRecord\":" <> J.encode testNameRecord <> "}"
+      "{\"type\":\"registered\",\"expires\":1813853483,\"graceUntil\":1821629483,\"reservedReason\":\"internal\",\"nameRecord\":" <> J.encode testNameRecord <> "}"
     answers body a =
       withResolverServer (resolveResp status200 body) $ \port _ -> do
         env <- newNamesEnv (testNamesConfig port)