Fix crypto subtype for trades api (#1022)

* fix: crypto subtype not persisted by permitting :subtype in CryptosController

* Backfill crypto subtype for existig accounts so Trades API works

* fix: backfill only unlinked cryptos; use raw SQL in migration; deterministic redirect in test

* Update schema.rb for BackfillcryptoSubtypeForTrades migration

---------

Signed-off-by: dataCenter430 <161712630+dataCenter430@users.noreply.github.com>

db/migrate/20260218120000_backfill_crypto_subtype_for_trades.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+class BackfillCryptoSubtypeForTrades < ActiveRecord::Migration[7.2]
+  def up
+    # Crypto accounts created via the UI before the controller permitted :subtype
+    # had subtype NULL, so supports_trades? was false and the Trades API returned 422.
+    # Backfill to "exchange" only for manual (unlinked) crypto accounts so they can use
+    # the Trades API. Skip accounts linked to a provider (e.g. CoinStats wallet) which
+    # intentionally leave subtype NULL and must remain wallet/sync-only.
+    # Uses raw SQL to avoid coupling to the Crypto model (see Rails migration guidelines).
+    say_with_time "Backfilling crypto subtype for manual accounts only" do
+      execute <<-SQL.squish
+        UPDATE cryptos
+        SET subtype = 'exchange'
+        WHERE subtype IS NULL
+          AND id IN (
+            SELECT a.accountable_id
+            FROM accounts a
+            WHERE a.accountable_type = 'Crypto'
+              AND NOT EXISTS (SELECT 1 FROM account_providers ap WHERE ap.account_id = a.id)
+          )
+      SQL
+    end
+  end
+
+  def down
+    # No-op: we cannot distinguish backfilled records from user-chosen "exchange",
+    # so reverting would incorrectly clear legitimately set subtypes.
+  end
+end