Python: Fix workflow kwargs collision with __global__ executor IDs

[WhaleTech (ryo-whaletech)]

Motivation & Context

Workflow invocation kwargs historically use __global__ both as a global namespace sentinel and as an executor-specific key. That shared key can allow executor-specific __global__ values to overwrite true globals; when a real executor has that ID, its targeted kwargs can also leak to sibling executors.

This fixes the namespace collision reported in #8310 while retaining the historical state representation for older consumers and checkpoints.

Description & Review Guide

• What are the major changes?

  • Store collision-free resolved kwargs in separate global and executor-specific namespaces while retaining the historical state representation for compatibility.
  • Centralize executor-ready kwargs conversion in Core and reuse it from AgentExecutor, GroupChat, and updated Declarative workflows.
  • Preserve raw caller input for nested workflow classification and retain Declarative's historical forwarding path when resolved state is absent.

• What is the impact of these changes?

  • Real __global__ executors receive their targeted kwargs plus true global kwargs without leaking values to siblings.
  • True global kwargs are no longer overwritten by executor-specific __global__ values.
  • Flat global mappings, ordinary per-executor mappings, legacy mixed mappings, and specific-over-global precedence remain compatible.
  • Older consumers and legacy checkpoints continue to receive the historical representation.

• What do you want reviewers to focus on?

  • The separation between the compatibility state and the collision-free resolved state.
  • The fallback boundary for older Declarative/Core combinations.
  • Shared routing behavior across AgentExecutor, GroupChat, Declarative, nested workflows, and checkpoints.

Related Issue

Fixes #8310

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

🟡 Changes recommended

Declarative workflow executors cannot consume the new non-mapping state object and will fail when forwarding invocation kwargs.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Introduces collision-free workflow kwargs routing while preserving legacy checkpoint compatibility.

Changes:

• Separates global and executor-specific kwargs.
• Updates nested workflow and agent resolution.
• Adds routing and checkpoint regression tests.

File summaries

File	Description
_const.py	Defines structured resolved kwargs.
_workflow.py	Normalizes invocation kwargs.
_workflow_executor.py	Forwards kwargs to nested workflows.
_agent_executor.py	Resolves kwargs for agents.
test_workflow_kwargs.py	Adds routing and restoration coverage.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Balanced

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[Copilot]

🟡 Changes recommended

Plain mixed global and executor-specific mappings no longer preserve their established merge behavior.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 1
• Review effort level: Balanced