FKN SHITSTATION AND THEIR GODDAMN SANDBOX BS - Sandbox will be it's own separate entity

app/config.py

@@ -319,16 +319,25 @@ def is_shipstation_test_mode() -> bool:
 def get_shipstation_setting(key: str) -> str:
     """
     Test-mode-aware lookup for ShipStation-related settings (API key,
-    store/warehouse/carrier IDs). When SHIPSTATION_TEST_MODE is on, looks
-    for a TEST_{key} override first, falling back to the normal {key}
-    value if the override is blank - so test mode works immediately if
-    your test/sandbox account mirrors production's store/warehouse/
-    carrier IDs, while still letting you override specific values if your
-    test account uses different ones. When test mode is off, this is
-    identical to config.get(key).
+    store/warehouse/carrier IDs, service codes). When SHIPSTATION_TEST_MODE
+    is on, ONLY the TEST_{key} value is used - no fallback to the
+    production value. When test mode is off, this is identical to
+    config.get(key).
+
+    This used to fall back to the production value when the TEST_ override
+    was blank, on the theory the sandbox might share IDs with production.
+    Confirmed against ShipStation's own docs that it never does - "Sandbox
+    data is isolated from production data... anything you create in the
+    sandbox will not be accessible in production, or vice-versa." A
+    fallback to a production store/warehouse/carrier ID under a sandbox API
+    key isn't a convenience, it's a guaranteed rejection - and it's exactly
+    what produced three separate confusing "not found"/"invalid" errors in
+    a row (carrier, then warehouse, then store) before this was caught.
+    Every caller of this function already raises a clear, specific
+    "X is not configured" error when it gets back an empty string, so
+    isolating test mode fully just turns those three confusing
+    ShipStation-side rejections into one obvious message instead.
     """
     if is_shipstation_test_mode():
-        test_value = get(f"TEST_{key}", "")
-        if test_value:
-            return test_value
+        return get(f"TEST_{key}", "")
     return get(key, "")