[Md. Shalah Uddin (shanto462)]

Motivation & Context

is_type_compatible had no case for a Literal source type. Its origin, typing.Literal, is not a class, so the check fell through to "different container types" and returned False. Edge validation then rejected a workflow where an executor sends Literal["approve", "reject"] to an executor that handles str, even though the runtime check is_instance_of already accepts these messages (#8351).

Description & Review Guide

• What are the major changes? A new case in is_type_compatible, before the union handling: a Literal source is compatible when every literal value fits the target, or one of its union members. A Literal member is checked by value with is_instance_of (same type and value, so True does not match Literal[1], as at runtime); any other member is checked with is_type_compatible(type(value), member), exactly how a plain str or int source is checked today. Tests cover Literal to str, int and bytes, mixed literals to a union, Literal[None] to Optional[str], a literal subset, Optional[Literal[...]], a union with a NewType member, an enum literal, list[Literal[...]], the rejected cases (including NewType and TypeVar targets), and a workflow that connects a Literal sender to a str handler.
• What is the impact of these changes? Workflows whose executors send Literal types to executors handling the literal values' type now build. str to a Literal target is still rejected, and other type pairs are unchanged.
• What do you want reviewers to focus on? The check runs before the union cases on purpose: checking each literal value on its own handles a mixed literal such as Literal["a", 1] against str | int, where no single union member accepts the whole literal. Non-Literal targets go through is_type_compatible rather than isinstance, so targets such as a NewType, a TypeVar or a non-runtime Protocol return False instead of raising during build(). One small change for Literal sources: Literal[True] against Literal[1] now returns False (it was True through ==), matching the runtime check.

Related Issue

Fixes #9354

No other open PR covers this issue.

AI Assistance

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AI assistance details: issue analysis, implementation, tests, 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 focused implementation matches runtime semantics and is comprehensively covered by regression tests.

0 open findings

What changed in this PR

Adds Literal source-type support to workflow edge compatibility validation.

Changes:

• Validates each literal value against target types and union members.
• Preserves strict Literal value-type matching.
• Adds utility and workflow regression tests.

File	Description
python/​packages/​core/​agent_framework/​_workflows/​_typing_utils.py	Implements Literal source compatibility.
python/​packages/​core/​tests/​workflow/​test_typing_utils.py	Covers compatible and rejected type combinations.
python/​packages/​core/​tests/​workflow/​test_validation.py	Verifies workflow construction with a Literal sender.

🧠 Review effort: Balanced

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