[BUG] @ parsing not work when a char before @

[NaccOll]

Problem (one or two sentences)

#7876 changes @mention parsing, but not inserts a space before @ when the user actively uses it. Furthermore, dragging files into the chat box doesn't insert a space, which causes confusion.

This is because if the user enters anything and doesn't actively press the spacebar, highlighting won't work when dragging files or using @ to reference them and parse not work

Context (who is affected and when)

All users who reference files using @

Reproduction steps

Open Chat, enter any content, and then reference the file by @ or dragging and dropping the file. It is found that the file will not be parsed and LLM needs to read the file.

Expected result

When users actively use @ or drag and drop files, they can directly reference files without manually inserting spaces before @.

Actual result

When there is a character in front, actively using @ or dragging and dropping files can only generate normal text with @.

Variations tried (optional)

No response

App Version

3.28.3

API Provider (optional)

Not Applicable / Other

Model Used (optional)

N/A

Roo Code Task Links (optional)

No response

Relevant logs or errors (optional)

[roomote]

I'm exploring a potential fix for the @mention parsing issue where spaces are not automatically inserted before @ when using mentions or dragging files. I'll open a PR to share progress.

[roomote]

Opened PR #8064 with my attempt at addressing this issue. The fix automatically inserts a space before @ mentions when needed, while maintaining the regex restriction from PR #7876 that prevents accidental parsing in pasted logs. All CI checks have passed. Feedback welcome!