When the terminal drops the ESC[201~ end mark during a bracketed paste
(terminal race, torn write, SSH glitch, macOS sleep/wake), prompt_toolkit's
Vt100Parser keeps buffering all later input in _paste_buffer forever. From
the user's perspective, the CLI appears frozen — the only recovery was
closing the tab/session.
This patch monkey-patches Vt100Parser.feed() so that bracketed-paste mode
flushes buffered content as a normal BracketedPaste event after 2 seconds
without an end marker, then restores normal parsing.
Includes 8 regression tests covering normal paste, timeout recovery,
torn end marks, and edge cases.
Surgical reapply of PR #27518. Original branch was many months stale
(1193 files / 172k LOC of unrelated reverts); the substantive ~77 LOC
patch in cli.py plus the new 157-line test file were reapplied onto
current main with the contributor's authorship preserved via --author.
