fix(security): enforce disabled flag on blocks in graph validation (#12059)

## Summary
Blocks marked `disabled=True` (like BlockInstallationBlock) were not
being checked during graph validation, allowing them to be used via
direct API calls despite being hidden from the UI.

This adds a security check in `_validate_graph_get_errors()` to reject
any graph containing disabled blocks.

## Security Advisory
GHSA-4crw-9p35-9x54

## Linear
SECRT-1927

## Changes
- Added `block.disabled` check in graph validation (6 lines)

## Testing
- Graphs with disabled blocks → rejected with clear error message
- Graphs with valid blocks → unchanged behavior

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<h2>Greptile Overview</h2>

<details><summary><h3>Greptile Summary</h3></summary>

Adds critical security validation to prevent execution of disabled
blocks (like `BlockInstallationBlock`) via direct API calls. The fix
validates that `block.disabled` is `False` during graph validation in
`_validate_graph_get_errors()` on line 747-750, ensuring disabled blocks
are rejected before graph creation or execution. This closes a
vulnerability where blocks marked disabled in the UI could still be used
through API endpoints.
</details>


<details><summary><h3>Confidence Score: 5/5</h3></summary>

- This PR is safe to merge and addresses a critical security
vulnerability
- The fix is minimal (6 lines), correctly placed in the validation flow,
includes clear security context (GHSA reference), and follows existing
validation patterns. The check is positioned after block existence
validation and before input validation, ensuring disabled blocks are
caught early in both graph creation and execution paths.
- No files require special attention
</details>


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<!-- /greptile_comment -->

---------

Co-authored-by: Nicholas Tindle <nicholas.tindle@agpt.co>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

autogpt_platform/backend/backend/data/graph.py

@@ -743,6 +743,11 @@ class GraphModel(Graph, GraphMeta):
                 # For invalid blocks, we still raise immediately as this is a structural issue
                 raise ValueError(f"Invalid block {node.block_id} for node #{node.id}")
 
+            if block.disabled:
+                raise ValueError(
+                    f"Block {node.block_id} is disabled and cannot be used in graphs"
+                )
+
             node_input_mask = (
                 nodes_input_masks.get(node.id, {}) if nodes_input_masks else {}
             )

autogpt_platform/backend/backend/executor/manager.py

@@ -213,6 +213,9 @@ async def execute_node(
         block_name=node_block.name,
     )
 
+    if node_block.disabled:
+        raise ValueError(f"Block {node_block.id} is disabled and cannot be executed")
+
     # Sanity check: validate the execution input.
     input_data, error = validate_exec(node, data.inputs, resolve_input=False)
     if input_data is None: