test: improve e2e tests and add COMPLETE_EXCHANGE permission tests

- Fix E2E test assertion for buy/sell direction change
- Add data-testid to date buttons for reliable e2e selection
- Update e2e tests to use data-testid instead of fragile weekday matching
- Add tests for regular user cannot complete/no-show trades (COMPLETE_EXCHANGE permission)

backend/tests/test_exchange.py

@@ -769,6 +769,68 @@ class TestAdminCompleteTrade:
         assert response.status_code == 400
         assert "not yet started" in response.json()["detail"]
 
+    @pytest.mark.asyncio
+    async def test_regular_user_cannot_complete_trade(
+        self, client_factory, regular_user, admin_user
+    ):
+        """Regular user cannot complete trades (requires COMPLETE_EXCHANGE permission)."""
+        # Create a past trade in DB
+        async with client_factory.get_db_session() as db:
+            past_time = datetime.now(UTC) - timedelta(hours=1)
+            exchange = Exchange(
+                user_id=regular_user["user"]["id"],
+                slot_start=past_time,
+                slot_end=past_time + timedelta(minutes=15),
+                direction=TradeDirection.BUY,
+                eur_amount=10000,
+                sats_amount=500000,
+                market_price_eur=20000.0,
+                agreed_price_eur=21000.0,
+                premium_percentage=5,
+                status=ExchangeStatus.BOOKED,
+            )
+            db.add(exchange)
+            await db.commit()
+            await db.refresh(exchange)
+            trade_id = exchange.id
+
+        # Regular user tries to complete
+        async with client_factory.create(cookies=regular_user["cookies"]) as client:
+            response = await client.post(f"/api/admin/trades/{trade_id}/complete")
+
+        assert response.status_code == 403
+
+    @pytest.mark.asyncio
+    async def test_regular_user_cannot_mark_no_show(
+        self, client_factory, regular_user, admin_user
+    ):
+        """Regular user cannot mark trades as no-show (requires COMPLETE_EXCHANGE permission)."""
+        # Create a past trade in DB
+        async with client_factory.get_db_session() as db:
+            past_time = datetime.now(UTC) - timedelta(hours=1)
+            exchange = Exchange(
+                user_id=regular_user["user"]["id"],
+                slot_start=past_time,
+                slot_end=past_time + timedelta(minutes=15),
+                direction=TradeDirection.BUY,
+                eur_amount=10000,
+                sats_amount=500000,
+                market_price_eur=20000.0,
+                agreed_price_eur=21000.0,
+                premium_percentage=5,
+                status=ExchangeStatus.BOOKED,
+            )
+            db.add(exchange)
+            await db.commit()
+            await db.refresh(exchange)
+            trade_id = exchange.id
+
+        # Regular user tries to mark as no-show
+        async with client_factory.create(cookies=regular_user["cookies"]) as client:
+            response = await client.post(f"/api/admin/trades/{trade_id}/no-show")
+
+        assert response.status_code == 403
+
 
 class TestAdminNoShowTrade:
     """Test admin marking trades as no-show."""

frontend/app/exchange/page.tsx

@@ -462,6 +462,7 @@ export default function ExchangePage() {
                   return (
                     <button
                       key={dateStr}
+                      data-testid={`date-${dateStr}`}
                       onClick={() => handleDateSelect(date)}
                       disabled={isDisabled}
                       style={{

frontend/e2e/exchange.spec.ts

@@ -79,11 +79,17 @@ test.describe("Exchange Page - Regular User Access", () => {
   test("clicking buy/sell changes direction", async ({ page }) => {
     await page.goto("/exchange");
 
-    // Click Sell BTC
+    // Initially in buy mode - summary shows BTC first: "You buy [sats], you sell €X"
+    // Verify buy mode is initially active
+    const buyButton = page.getByRole("button", { name: "Buy BTC" });
+    await expect(buyButton).toBeVisible();
+
+    // Click Sell BTC to switch direction
     await page.getByRole("button", { name: "Sell BTC" }).click();
 
-    // The summary should mention "You send" for sell
+    // In sell mode, the summary shows EUR first: "You buy €X, you sell [sats]"
-    await expect(page.getByText(/You send/)).toBeVisible();
+    // We can verify by checking the summary text contains "You buy €" (EUR comes first)
+    await expect(page.getByText(/You buy €\d/)).toBeVisible();
   });
 
   test("exchange page shows date selection", async ({ page }) => {
@@ -112,17 +118,9 @@ test.describe("Exchange Page - With Availability", () => {
   test("shows available slots when availability is set", async ({ page }) => {
     await page.goto("/exchange");
 
-    // Get tomorrow's display name to click the correct button
+    // Use data-testid for reliable date selection
-    const tomorrow = new Date();
+    const tomorrowStr = getTomorrowDateStr();
-    tomorrow.setDate(tomorrow.getDate() + 1);
+    const dateButton = page.getByTestId(`date-${tomorrowStr}`);
-    const weekday = tomorrow.toLocaleDateString("en-US", { weekday: "short" });
-
-    // Click tomorrow's date using the weekday name
-    // Wait for the button to be enabled (availability loading must complete)
-    const dateButton = page
-      .locator("button")
-      .filter({ hasText: new RegExp(`^${weekday}`) })
-      .first();
     await expect(dateButton).toBeEnabled({ timeout: 15000 });
     await dateButton.click();
 
@@ -140,16 +138,9 @@ test.describe("Exchange Page - With Availability", () => {
   test("clicking slot shows confirmation form", async ({ page }) => {
     await page.goto("/exchange");
 
-    // Get tomorrow's display name
+    // Use data-testid for reliable date selection
-    const tomorrow = new Date();
+    const tomorrowStr = getTomorrowDateStr();
-    tomorrow.setDate(tomorrow.getDate() + 1);
+    const dateButton = page.getByTestId(`date-${tomorrowStr}`);
-    const weekday = tomorrow.toLocaleDateString("en-US", { weekday: "short" });
-
-    // Click tomorrow's date - wait for button to be enabled first
-    const dateButton = page
-      .locator("button")
-      .filter({ hasText: new RegExp(`^${weekday}`) })
-      .first();
     await expect(dateButton).toBeEnabled({ timeout: 15000 });
     await dateButton.click();
 
@@ -169,16 +160,9 @@ test.describe("Exchange Page - With Availability", () => {
   test("confirmation shows trade details", async ({ page }) => {
     await page.goto("/exchange");
 
-    // Get tomorrow's display name
+    // Use data-testid for reliable date selection
-    const tomorrow = new Date();
+    const tomorrowStr = getTomorrowDateStr();
-    tomorrow.setDate(tomorrow.getDate() + 1);
+    const dateButton = page.getByTestId(`date-${tomorrowStr}`);
-    const weekday = tomorrow.toLocaleDateString("en-US", { weekday: "short" });
-
-    // Click tomorrow's date - wait for button to be enabled first
-    const dateButton = page
-      .locator("button")
-      .filter({ hasText: new RegExp(`^${weekday}`) })
-      .first();
     await expect(dateButton).toBeEnabled({ timeout: 15000 });
     await dateButton.click();