Editing a message makes user and channel mentions break

(#421) Bug Awaiting confirmation messaging

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Comment by @cproudlock
RexSystem 1 vote originally by @cproudlock on GitHub
The issue is in how the message editor reconstructs mentions from display text. When a message is loaded for editing, fluxer_app/src/utils/MarkdownToSegmentUtils.tsx (convertMarkdownToSegments, line 39) correctly parses the raw markdown mention syntax (e.g. <@12345>) and creates segments. However, the segment state isn't properly persisted through the edit lifecycle. When the user saves the edit, displayToActual() in the textarea segments hook converts from the display text back to raw markdown — but it doesn't properly reconstruct the <@id> format for mentions that were in the original message. The fix would be to ensure that when loading a message for editing in EditingMessageInput.tsx (around line 130-146), the segments created by convertMarkdownToSegments are fully registered in the segment manager so that displayToActual() can reconstruct them on save.