Change Details

As a first step of separating logic into message-specs to determine whether messages can be sidebar sources / can be pinned / etc, we should first dedup `isMessageSidebarSourceReactionEditOrPin` into `isInvalidSidebarSource` since the checks are the same. Addresses Part 1a of [[ https://linear.app/comm/issue/ENG-4849/thread-from-robotext-about-pinned-message-causing-errors#comment-36f2e045 | ENG-4849 ]]

As a first step of separating logic into message-specs to determine whether messages can be sidebar sources / can be pinned / etc, we should first dedup `isMessageSidebarSourceReactionEditOrPin` into `isInvalidSidebarSource` since the checks are the same. Addresses Part 1a of [[ https://linear.app/comm/issue/ENG-4849/thread-from-robotext-about-pinned-message-causing-errors#comment-36f2e045 | ENG-4849 ]]

As a first step of separating logic into message-specs to determine whether messages can be sidebar sources / can be pinned / etc, we should first dedup `isMessageSidebarSourceReactionEditOrPin` into `isInvalidSidebarSource` since the checks are the same. Addresses Part 1a of [[ https://linear.app/comm/issue/ENG-4849/thread-from-robotext-about-pinned-message-causing-errors#comment-36f2e045 | ENG-4849 ]]