Fix cmd-click crash when command-mark data is unavailable

[onemedicine]

Summary

• guard VT100ScreenState command-mark lookup against out-of-bounds coordinates, missing marks, and missing interval-tree entries
• let command-click URL resolution fall through cleanly when command-mark data is unavailable instead of crashing
• add targeted VT100ScreenTests coverage for the out-of-bounds and no-mark cases, and document the fix in the 3.7 release notes

Test plan

• make paranoid-deps
• tools/run_tests.expect ModernTests/VT100ScreenTests/testCommandMarkAtReturnsNilWhenLineIsOutOfBounds ModernTests/VT100ScreenTests/testCommandMarkAtReturnsNilWhenNoMarkOnLine

Notes

• I rebased this to the current master so the PR is a single fix commit on top of upstream.

[Copilot]

Pull request overview

This PR hardens command-mark lookup in VT100ScreenState so Cmd-click URL/prompt resolution can gracefully fall back when command-mark data is missing or inconsistent, avoiding a crash in the terminal interaction flow.

Changes:

• Add bounds/validity guards in VT100ScreenState -commandMarkAt:mustHaveCommand:range: for out-of-range coordinates, missing marks, and missing interval-tree entries.
• Add targeted VT100ScreenTests coverage for out-of-bounds and no-mark cases.
• Document the crash fix in the 3.7 release notes.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
sources/VT100Screen/VT100ScreenState.m	Adds defensive checks so command-mark lookup returns nil instead of crashing when mark data is unavailable/invalid.
ModernTests/VT100ScreenTests.swift	Adds regression tests covering out-of-bounds and no-mark command-mark lookups.
docs/notes-3.7.txt	Notes the Cmd-click crash fix in the 3.7 bug fixes section.

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[gnachman]

Thank you! This is a clean, well-guarded fix, and I appreciate the thorough regression tests covering the out-of-bounds, no-mark, and mark-without-command paths (and for addressing the review note about mustHaveCommand). All three tests pass here. Merged (squashed) as f036dee, with you as the author.