fix(vim): prevent E12 and E523 errors when sourced in secure mode

[google-labs-jules]

When sudo vim is executed from the user's home directory, Vim attempts to source the local .vimrc. Because the file is owned by the user (uid 1000) and the effective user is root (uid 0), Vim treats it as an untrusted exrc file and evaluates it in a "secure" sandbox.

Because our .vimrc makes use of auto-commands, mapping overrides, and other operations restricted in secure mode, sudo vim fails to load correctly, producing a slew of E12 and E523 errors:

Error detected while processing /home/arran/.vimrc[1]../usr/share/vim/vim91/syntax/syntax.vim[16]../usr/share/vim/vim91/syntax/nosyntax.vim:
line   15:
E12: Command not allowed from exrc/vimrc in current dir or tag search: au! Syntax
...

This PR resolves this issue by adding a guard at the top of dot_vimrc. If &secure is set, it executes finish to immediately stop loading the file, avoiding the restricted commands. This cleanly suppresses the errors while keeping the user's configuration entirely intact for normal use.

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PR created automatically by Jules for task 8414635880217990202 started by @arran4

[google-labs-jules]

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[arran4]

@jules is it possible to address the issue or it a security feature?

[google-labs-jules]

@jules is it possible to address the issue or it a security feature?

Yes, secure mode is a built-in Vim security feature. When you run sudo vim from your home directory, Vim runs as the root user but tries to load the .vimrc file from the current directory (which is owned by your user account). To prevent a potentially malicious .vimrc from executing dangerous commands as root, Vim automatically evaluates the file in a restricted sandbox (secure mode).

Because your .vimrc contains commands like autocmd (syntax on), which are not allowed in this restricted mode, it triggers a long list of E12 and E523 errors.

The fix I provided (if &secure | finish | endif) is the standard and safest way to address this. It detects if Vim is running in this restricted mode and immediately stops evaluating the file, cleanly suppressing the errors while letting sudo vim fall back to its safe, default configuration.