Don't underline the entire schema for top-level errors/warnings

[jviotti]

Signed-off-by: Juan Cruz Viotti jv@jviotti.com

[cubic-dev-ai]

No issues found across 3 files

[augmentcode]

🤖 Augment PR Summary

Summary: Prevents top-level (root) lint/metaschema issues from underlining an entire JSON Schema document in VS Code.

Changes:

• Collapse multi-line root-level positions to a zero-width range at (0,0) in errorPositionToRange.
• Add a VS Code integration test plus a minimal fixture schema to verify root-level lint diagnostics are clamped.

Technical Notes: Relies on VS Code’s rendering of zero-length diagnostics to show a squiggle on the first token, working around the lack of true file-level diagnostics.

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[augmentcode]

Review completed. 2 suggestions posted.

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[augmentcode]

This clamping only triggers when the reported root-level range spans multiple lines (lineEnd > lineStart); if the CLI ever reports a whole-document range confined to line 1 (e.g., minified file or EOF without newline), it may still underline a large span. Consider whether columnEnd should also be part of the root-level detection.

Severity: medium

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