Top-left pill overlay on every code block (opposite corner from the
engine's own copy button) showing the current language; tapping opens
a curated ~20-language menu that rewrites just the fence line,
content untouched.
New engine mechanism to support it: CodeBlockSelection now exposes
fenceRange (the opening ```lang line's range, straight from the
tokenizer's own markerRanges[0] - was already computed, just never
exposed) plus a generic TextRangeReplacementRequest/
pendingTextRangeReplacement, since the existing pendingTextInsertion
only replaces at the current caret/selection, not an arbitrary
already-known range like a fence line the user isn't necessarily
positioned at.
Horizontal scroll for long lines investigated and dropped, per
explicit instruction after weighing it: the only viable path (a real,
selectable/editable independently-scrolling text region) needs an
embedded NSTextAttachmentViewProvider-backed NSTextView per code
block, which would split selection/copy/undo into two contexts
(the code block's own vs. the surrounding document's) instead of one
unified editing surface - a different regression, not a clean win.
Code blocks keep wrapping.
Puranjay Savar Mattas
283186b28f