[bhabishnu]

Issue:

Fixes #4356

Loop protection currently regenerates the whole sketch after modifying the AST. That changes the original source layout by removing comments and blank lines and reformatting the code, so runtime errors can end up pointing to the wrong line in the editor.

Changes:

• Keep using the Acorn AST to locate loops, but insert the protection code directly into the original source at those AST offsets.
• Apply edits from the end of the file backwards so earlier insertions don't shift the remaining offsets.
• Keep the inserted protection code on the existing lines so the original line numbers are preserved.
• Add regression coverage for the original repro, nested and brace-less loops, shared edit positions, and infinite-loop protection.

AI tools were used as an assistive tool during investigation and implementation. I reviewed the final diff and verified the behaviour and tests locally.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123
• meets the standards outlined in the accessibility guidelines

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[davepagurek]

This looks good to me! I'm going to get a web editor maintainer to take a look too to make sure there's nothing else I'm missing.