Upgrade allow_external warning to error

Author: EdwardJXLi

docs/introduction/advanced-settings.mdx

@@ -309,9 +309,9 @@ Controls import path overrides during import resolution.
 
 Enables and disables resolution of imports from `sys.path`.
 
-<Note>
-For this to properly work, you may also need to enable `allow_external`.
-</Note>
+<Warning>
+For this to properly work, you must also set `allow_external` to `True`.
+</Warning>
 
 ## Flag: `allow_external`
 > **Default: `False`**

src/codegen/sdk/core/codebase.py

@@ -213,6 +213,13 @@ def __init__(
         self.ctx = CodebaseContext(projects, config=config, secrets=secrets, io=io, progress=progress)
         self.console = Console(record=True, soft_wrap=True)
 
+        # Assert config assertions
+        # External import resolution must be enabled if syspath is enabled
+        if self.ctx.config.py_resolve_syspath:
+            if not self.ctx.config.allow_external:
+                msg = "allow_external must be set to True when py_resolve_syspath is enabled"
+                raise ValueError(msg)
+
     @noapidoc
     def __str__(self) -> str:
         return f"<Codebase(name={self.name}, language={self.language}, path={self.repo_path})>"