core: reject dashes in isolation instance names:

To avoid confusion and hard-to-debug behaviours, `-` are now rejected in isolation
instance names, only `_` is accepted.

libervia/backend/core/constants.py

@@ -57,12 +57,18 @@ class Const:
     isolation_name = os.environ.get("LIBERVIA_ISOLATION")
 
     if isolation_name:
-        # Validate isolation name: only allow [A-Za-z0-9_-] to prevent path traversal and
+        # Validate isolation name: only allow [A-Za-z0-9_] to prevent path traversal and
         # other issues.
-        if not isolation_name.replace("-", "").replace("_", "").isalnum():
+        if "-" in isolation_name:
+            raise ValueError(
+                f"Invalid LIBERVIA_ISOLATION name {isolation_name!r}: dashes are"
+                f" not allowed, please use underscores instead"
+                f" ({isolation_name.replace('-', '_')!r})"
+            )
+        if not isolation_name.replace("_", "").isalnum():
             raise ValueError(
                 f"Invalid LIBERVIA_ISOLATION name {isolation_name!r}, "
-                f"must only contain [A-Za-z0-9_-]"
+                f"must only contain [A-Za-z0-9_]"
             )
         isolation_mode = os.environ.get("LIBERVIA_ISOLATION_MODE", "normal").lower()
         match isolation_mode: