fix(block): Avoid infinite loop execution on AddToListBlock self-loop (#9629)

### Changes 🏗️

<img width="757" alt="image"
src="https://github.com/user-attachments/assets/909aab58-24c7-42ec-9580-ac3e9f32057e"
/>

Since a self-loop is now allowed for AddToListBlock, providing an entry
pin using a static output will cause infinite execution.
This PR change avoid such scenario to be allowed.

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  <!-- Put your test plan here: -->
  - [x] Described above

autogpt_platform/backend/backend/blocks/basic.py

@@ -468,11 +468,27 @@ class AddToListBlock(Block):
 
         @classmethod
         def get_missing_links(cls, data: BlockInput, links: List["Link"]) -> set[str]:
+            # If `list` self-loop present, the `entry` pin can't be static.
+            list_self_loop_present = any(
+                link.sink_name == "list" and link.sink_id == link.source_id
+                for link in links
+            )
+            entry_static_output_present = any(
+                link.sink_name == "entry" and link.is_static for link in links
+            )
+            if list_self_loop_present and entry_static_output_present:
+                raise ValueError(
+                    "The `entry` pin can't have static output from `AgentInput` or "
+                    "`StoreValue` block as long as the `list` pin has a self-loop."
+                    "This will cause an infinite execution loop."
+                )
+
             return super().get_missing_links(
                 data,
                 [
                     link
                     for link in links
+                    # Allow execution with `list` pin self-loop
                     if link.sink_name != "list" or link.sink_id != link.source_id
                 ],
             )