[Feature]: Add support for filtering unassigned tasks #557
Description
Is your feature request related to a problem? Please describe.
When listing tasks, there is no way to filter for unassigned tasks. The assignee parameter only matches against a specific
assignee name, so finding all tasks with no assignee assigned requires fetching the full list and filtering manually.
Describe the solution you'd like
Support a special sentinel value (e.g. assignee: "none" or assignee: "") in task_list that returns only tasks where no
assignee is set. Alternatively, add a boolean unassigned: true parameter.
Additional context
This is particularly useful for AI agents picking up work from a shared backlog — they need to find tasks not yet claimed by
a human before starting work. Tried "", "unassigned", and "Unassigned" — all return no results rather than filtering for
truly unassigned tasks.