[DEMO - SCALE 23X] Modifiable node inputs

[mkmeral]

Problem Statement

Please note that this is a temporary ticket meant for live demo during Scale 23X conference

Allow to customize node inputs for graph structure

Proposed Solution

No response

Use Case

I want to be able to customize my node inputs in graphs, before they are sent to the agent

Alternatives Solutions

No response

Additional Context

No response

[mkmeral]

/strands

[github-actions]

Repository Analysis & Clarifying Questions

I've analyzed the repository structure and have identified the implementation approach for modifiable node inputs in graphs. Here's my analysis and some questions:

Repository Context

• Current Flow: The _build_node_input() method in graph.py constructs node inputs from either the original task (for entry points) or from task + outputs from previous nodes
• Existing Patterns: The codebase already has hooks that allow modification before execution:
  • BeforeToolCallEvent allows modifying selected_tool, tool_use
  • BeforeInvocationEvent allows modifying messages
  • BeforeNodeCallEvent exists but currently only has cancel_node as writable

Proposed Implementation

Extend BeforeNodeCallEvent to include a node_input field that hooks can modify before the node executes. This follows the existing pattern in the codebase and would require changes to:

1. src/strands/hooks/events.py - Add node_input field to BeforeNodeCallEvent
2. src/strands/multiagent/graph.py - Use the modified input from the event
3. Unit and integration tests

Clarifying Questions

Implementation Approach

1. Hook-based vs Builder Pattern: Should this be implemented through the hook system (extending BeforeNodeCallEvent) or via a builder pattern (e.g., GraphBuilder.set_input_transformer(node_id, transformer_fn))? The hook approach is more consistent with existing patterns.

2. Input Type: What type should the modifiable input be?

   • list[ContentBlock] (current internal format)
   • str | list[ContentBlock] (more flexible)
   • Both with automatic conversion?

3. Validation: Should there be validation of the modified input, or should it be passed directly to the node executor?

Scope & Timeline

4. Scale 23X Demo Timeline: What's the target date for the Scale 23X conference demo? This will help prioritize the implementation.

5. Additional Requirements: Beyond input modification, are there any other graph customization features needed for the demo (e.g., output transformation, conditional routing based on modified inputs)?

Scope Assessment

This appears to be a well-scoped feature that:

• Follows existing patterns in the codebase
• Can be implemented in 1-2 days
• Is appropriate for a single PR
• Does not require GitHub workflow changes

[mkmeral]

/strands implement hook based approach

[github-actions]

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[github-actions]

Implementation completed for the hook-based approach to modifiable node inputs.

Changes:

• Added node_input writable property to BeforeNodeCallEvent in hooks
• Graph now builds node input BEFORE invoking hooks, passing it to the event
• Hooks can modify event.node_input to customize what the agent receives

Example usage:

class MyHook(HookProvider):
    def on_before_node_call(self, event: BeforeNodeCallEvent) -> None:
        # Modify the input before it reaches the agent
        event.node_input = [{"text": f"[Custom Context] {event.node_input[0]['text']}"}]

A pull request has been created with the implementation and tests.