CodeMirror collapses a CRLF pair into one line break, so the document is
shorter than the string it was given. The composer derived the caret from
the JS string length, which put it past the end of the document and made
dispatch throw `RangeError: Selection points outside of document`.
Because the exception fires before the transaction applies, the document
never updates, the un-normalized text stays in React state, and the draft
persists as-is: every later visit to the session restores it and crashes
again, with no way out from the UI.
Derive the caret from the change set instead, in the controlled writeback
and in the imperative insert/replace handles.
fixes#3013
# Conflicts:
# CHANGELOG.md
# packages/vscode/CHANGELOG.md
Iuliia Ivashko
eca9353382