feat(graph): add edge_execution_mode toggle for AND/OR predecessor logic

[dbschmigelski]

Description

• Add EdgeExecutionMode enum with OR (default) and AND modes to control when graph nodes become ready to execute
• Fix latent bug in _compute_ready_nodes_for_resume that always used AND logic regardless of intended behavior

Motivation

Currently, when multiple nodes connect to a target node, the target executes as soon as ANY predecessor completes (OR logic). Users need the ability to wait for ALL predecessors to complete before executing (AND logic) for fan-in/join patterns.

  # A, B, C all connect to Z
  builder = GraphBuilder()
  builder.add_node(agent_a, "A")
  builder.add_node(agent_b, "B")
  builder.add_node(agent_c, "C")
  builder.add_node(agent_z, "Z")
  builder.add_edge("A", "Z")
  builder.add_edge("B", "Z")
  builder.add_edge("C", "Z")
  builder.set_entry_point("A")
  builder.set_entry_point("B")
  builder.set_entry_point("C")

  # OR mode (default): Z executes when ANY of A, B, C completes
  # AND mode: Z waits until ALL of A, B, C complete
  builder.set_edge_execution_mode(EdgeExecutionMode.AND)

  graph = builder.build()

Bug Fix

_compute_ready_nodes_for_resume previously used all() unconditionally, meaning resume always applied AND logic even though the default behavior is OR. This is now fixed to respect the edge_execution_mode setting.

Related Issues

#1081

Documentation PR

None

Type of Change

New feature

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[codecov]

Codecov Report

❌ Patch coverage is 97.36842% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/strands/multiagent/graph.py	97.05%	0 Missing and 1 partial ⚠️

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