[M-Hietala]

Motivation & Context

Workflow validation rejects valid connections such as list[str] -> Sequence[str] because the parameterized container types have different origins. This also prevents Workflow.as_agent() from accepting a start handler typed as Sequence[Message], even though the supplied message list satisfies that interface.

Description & Review Guide

• What are the major changes? Update is_type_compatible to recognize parameterized collection interfaces implemented by list, set, frozenset, and dict, recursively checking their corresponding type arguments. For single-argument dictionary interfaces such as Iterable, check the key type. Add parameterized compatibility tests and workflow regressions for a Sequence[str] handler and a Sequence[Message] start handler used through as_agent().
• What is the impact of these changes? Valid connections such as list[str] -> Sequence[str], dict[str, int] -> Mapping[str, int], and set[int] -> Set[int] are accepted. Incompatible element types remain rejected, and existing unparameterized-container behavior is unchanged. Tuple-to-interface compatibility remains outside this change.
• What do you want reviewers to focus on? The direction of compatibility checks, recursive argument validation, dictionary-key handling for iterable interfaces, and the deliberately bounded set of supported source containers.

Related Issue

Fixes #9449

AI Assistance

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AI assistance details: Copilot assisted with implementation, focused validation, and this PR description.

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 links to an agreed issue with no competing open PR, or the Related Issue section documents a trivial-change or repository-automation exception.
• 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]

🟢 Approval recommended

The narrowly scoped implementation preserves compatibility direction and recursive validation, with focused regression coverage and no blocking issues identified.

No open issues 🎉

What changed in this PR

This PR fixes workflow type validation for parameterized collection interfaces, addressing #9449 and allowing Sequence[Message] start handlers through Workflow.as_agent().

Changes:

• Accepts compatible collection interfaces for list, set, frozenset, and dict, recursively checking type arguments.
• Uses dictionary key types for single-argument interfaces while preserving existing bare-container behavior and excluding tuples.
• Adds compatibility tests and end-to-end workflow regressions.

File	Description
python/​packages/​core/​tests/​workflow/​test_workflow_builder.py	Adds workflow execution and agent regressions for sequence handlers.
python/​packages/​core/​tests/​workflow/​test_typing_utils.py	Tests compatible and incompatible parameterized collection types.
python/​packages/​core/​agent_framework/​_workflows/​_typing_utils.py	Adds bounded collection-interface compatibility checks.

_{Review effort: Balanced}

[Eduard van Valkenburg (eavanvalkenburg)]

M-Hietala Runtime compatibility now accepts parameterized collection interfaces, but handler dispatch still matches only the collection origin. If a destination has Sequence[str] and Sequence[int] handlers, an upstream list[int] can pass validation and then select the first Sequence handler—the string handler—causing a runtime failure. Please validate element, key, and value type arguments during runtime matching, and add a workflow regression with differently parameterized collection handlers.