fix: resolved isntrument bug on table

db/schema/schema.sql

@@ -1,12 +1,13 @@
 CREATE TABLE IF NOT EXISTS instruments (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
-    symbol TEXT NOT NULL UNIQUE,
+    symbol TEXT NOT NULL,
     asset_type TEXT NOT NULL,
     exchange TEXT,
     quote_currency TEXT NOT NULL,
     created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
     updated_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
-    deleted_at TIMESTAMP
+    deleted_at TIMESTAMP,
+    UNIQUE(symbol, exchange)
 );
 
 CREATE TABLE IF NOT EXISTS portfolios (

internal/db/migrations/20260411114506_internal_db_migrations_sqlite.initial_setup.sql

@@ -2,13 +2,14 @@
 -- +goose StatementBegin
 CREATE TABLE IF NOT EXISTS instruments (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
-    symbol TEXT NOT NULL UNIQUE,
+    symbol TEXT NOT NULL,
     asset_type TEXT NOT NULL,
     exchange TEXT,
     quote_currency TEXT NOT NULL,
     created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
     updated_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
-    deleted_at TIMESTAMP
+    deleted_at TIMESTAMP,
+    UNIQUE(symbol, exchange)
 );
 
 CREATE TABLE IF NOT EXISTS portfolios (

internal/repository/instrument_repo.go

@@ -73,7 +73,7 @@ func (r *InstrumentRepository) Create(ctx context.Context, in Instrument) (Instr
 				"instrument %q on exchange %q: %w",
 				in.Symbol,
 				in.Exchange,
-				domain.ErrPositionAlreadyExists,
+				domain.ErrInstrumentAlreadyExists,
 			)
 		}