[Manohar Paturi (ManoharPaturi)]

Motivation & Context

add_items signals both a missing conversation and unsupported item content with a plain ValueError, and the route answers every ValueError with 404. Posting a video-only item to an existing conversation therefore reported Not Found, which reads as a wrong conversation id rather than a request the client can fix.

Description & Review Guide

• What are the major changes? Unsupported item content now raises a ConversationItemValidationError (a ValueError subclass), and the items route maps it to 400 while a missing conversation stays 404.
• What is the impact of these changes? Only the status code for the malformed item case changes. Other handlers catching ValueError are unaffected because the new exception subclasses it.
• What do you want reviewers to focus on? The route test covers both cases against the HTTP surface: unsupported content on an existing conversation is 400, and an unknown conversation id is still 404.

Related Issue

Fixes #9506

AI Assistance

• No material AI assistance was used.
• This is an AI-assisted contribution. I reviewed, understood, and verified all submitted content and accept responsibility for it.

[Eduard van Valkenburg (eavanvalkenburg)]

The 400/404 exception split and route coverage are correct; only the import block needs to be made lint-clean.

[Eduard van Valkenburg (eavanvalkenburg)]

Please move this relative import below the complete fastapi import group, alongside the other local imports. Ruff enables the I/isort rules, so placing it between from fastapi import ... and from fastapi.middleware... leaves this file with an unsorted import block and will fail code quality.

[Manohar Paturi (ManoharPaturi)]

Moved: the conversations import now sits with the other local imports below the complete fastapi group, and ruff isort reports the block clean. Amended into the branch; the server suite still passes (51 tests).

[Manohar Paturi (ManoharPaturi)]

Thanks Eduard van Valkenburg (@eavanvalkenburg). I cleaned up the import block in _server.py so ConversationItemValidationError sits properly with the local package imports rather than interrupting the FastAPI group, and verified the file passes Ruff checks.

[Manohar Paturi (ManoharPaturi)]

The Public API Compatibility check fails on every open PR in this repo right now (e.g. #9602, #9607, and all of this author's open PRs), so it looks like a repo-wide CI issue rather than something introduced by this change.

The job crashes inside griffe while loading the base (main) snapshot, before it compares the PR changes — the traceback points at the base copy of the package:

griffe._internal.exceptions.AliasResolutionError: Could not resolve alias
agent_framework._workflows._edge.EdgeGroup.builtin_type pointing at builtins.type
(in /tmp/python-api-base-.../python/packages/core/agent_framework/_workflows/_edge.py:315)

Example run: https://github.com/microsoft/agent-framework/actions/runs/39810016173/job/119933441343

None of the changes in this PR touch _workflows/_edge.py. Filed an issue for the CI failure; happy to help debug if useful.