When old_string survives all 9 fuzzy strategies without a match but
the closest candidate line matches after stripping whitespace, the
failure is whitespace-shaped (tabs vs spaces, indent depth). The
did-you-mean hint now appends a two-line diagnosis with leading
whitespace made visible:
Whitespace difference detected (→ = tab, · = space):
file has: →def start(self):
you sent: ····def start(self):
Use the exact whitespace shown in 'file has'.
Pattern ported from crush's diagnoseMismatch (agent-codebase survey) —
it converts the residual dead-end error into a one-turn fix. Only the
leading run is visualized (interior spacing stays readable); content-
shaped misses and raw-exact candidates are unchanged.
Teknium