SD-3386 - fix: deletion handling across paragraph boundaries

[chittolinag]

Issue

In suggesting mode, deleting a selection that spans two paragraphs pushed the remainder of the second paragraph onto a new line, as if Enter was pressed. On the real Backspace/Delete keymap path the tracked interception could crash position mapping (RangeError: Position NaN), and the dispatch fallback then deleted the text untracked. Accepting or rejecting the change failed silently, leaving the inline decoration painted, and the hover bubble reported "Accepted" even after a reject.

Proposed solution

• ProseMirror describes a cross-paragraph deletion as a ReplaceStep carrying a structural paragraph re-join shell; the tracked-changes compiler misread that shell as replacement content, inserted it at the selection end (splitting the paragraph), and minted a malformed replacement the decision engine refuses. replaceStep.js now compiles slices without inline leaf content as plain tracked deletions, skips the invert/mirror mapping pairing for that mark-only compile (the source of the NaN), and emits an explicit caret hint at the deletion's left edge.
• Decision resolve events now carry which decision was taken; the comment model stores it and the resolved badge shows "Rejected" vs "Accepted". The bubble's accept/reject no longer mark the thread resolved when the underlying editor decision did not apply.
• Regression tests cover the command path, the real keymap path (Backspace and Delete), the accept/reject lifecycle, and the badge/resolve behavior.

[linear-code]

SD-3386

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.23810% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...perdoc/src/components/CommentsLayer/use-comment.js	80.00%	2 Missing ⚠️

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[chatgpt-codex-connector]

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