[Manohar Paturi (ManoharPaturi)]

Motivation & Context

The DevUI conversation create and update routes accepted any JSON value as metadata and stored it verbatim. A string or null value survived the write, and the first conversation list call after that crashed with an attribute error while copying stored metadata, taking the whole list endpoint down until restart while single conversation reads kept working, so the failure looked random. The Conversations API contract for metadata is a map of string keys to string values, and the boundary should enforce it.

Description & Review Guide

• What are the major changes? Both routes now run metadata through one shared validator that accepts only a map of string keys to string values and rejects every other shape with a 400, and an explicit null becomes an empty map so the store never holds a value the readers cannot copy.
• What is the impact of these changes? Writers sending valid metadata see no difference, invalid writes get a clear rejection instead of a delayed 500 for everyone, and existing stores are unaffected because validation happens before anything is stored.
• What do you want reviewers to focus on? The validation living at the route boundary rather than inside the store, since the store also serves internal callers that always pass well formed maps.

Related Issue

Fixes #9860

AI Assistance

• No material AI assistance was used.
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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.

[Manohar Paturi (ManoharPaturi)]

Understood, and sorry for jumping ahead. The issue now uses the Python bug report template with the verified reproduction, and I will leave this PR closed until the team agrees with the direction on #9860.