Port from cline/cline#13970: models that send patch calls with an empty
old_string got back 'old_string cannot be empty' — an error that names the
problem but not the recovery, so the next call was byte-identical and the
run burned turns until loop detection killed it (upstream repro: Kimi K3
looping on old_text: null).
The rejection now states the recovery: set old_string to the exact text the
replacement should replace, read the file first if unsure, use write_file
for new files/full rewrites, and do not re-send the call unchanged. The
whitespace-only rejection gets the same treatment. No behavior change for
valid calls.
e21a6fb159