fix: mention ping detection

[beladiyaraj]

What Changed

Fixed @ file/folder mentions in the message box.

1. Fixed the issue where @ mentions only worked at the end of the message.
2. Fixed the issue where adding one file mention could break a later @ mention in the same message.
3. Fixed the issue where typing a new @ could show old search results from the previous mention for the same message.
4. Improved the logic so file suggestions follow the actual cursor position more reliably when editing text around existing mentions.
5. Added regression tests for the broken mention flows we found.

Why

Previously:

• @ mentions could behave differently depending on where they were typed in the sentence.
• After selecting one file, going back and typing another @ could fail or behave inconsistently.
• A fresh @ could show stale results from the previous search instead of starting clean for the same message.

Now:

• @ mentions work more reliably anywhere in the message.
• Multiple mentions in the same message behave correctly.
• A new @ starts from a clean suggestion state and only shows current matches.

UI Changes

None

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

This PR fixes the issue #857

Note

Fix mention ping detection using expanded cursor in composer trigger resolution

• Introduces detectComposerTriggerFromSnapshot in composer-logic.ts, which prefers expandedCursor when available (falling back to expanding the collapsed cursor) before calling detectComposerTrigger.
• Adds mode-aware ('collapsed' | 'expanded') cursor measurement to getComposerNodeTextLength, getAbsoluteOffsetForPoint, and $readSelectionOffsetFromEditorState in ComposerPromptEditor.tsx so mention nodes contribute their full text length in expanded mode.
• The editor now tracks both a collapsed and expanded cursor position, passing nextExpandedCursor to the active pending user input answer callback.
• Adds resolveComposerPathMenuEntries in composer-path-menu.ts to hide path suggestions when the query is empty or while debouncing/fetching/loading.
• Behavioral Change: @path mention trigger detection now uses the expanded cursor position, which may change which trigger is detected when the cursor is adjacent to a mention node.

^{Macroscope summarized e1458c8.}

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[juliusmarminge]

conflicts

[juliusmarminge]

@macroscope-app review this

[juliusmarminge]

bug with cursor moving to the end when inserting a mention at the start:
https://github.com/user-attachments/assets/6cf8108e-f3ea-419d-8012-30208fcc9757

[beladiyaraj]

bug with cursor moving to the end when inserting a mention at the start: https://github.com/user-attachments/assets/6cf8108e-f3ea-419d-8012-30208fcc9757

Let me fix this

[juliusmarminge]

conflcits

[beladiyaraj]

Hey @juliusmarminge i think this has been fixed in the commit 71a7473

so we can close this without merge