Every ancestor cost a manifest read and a full-file line diff — ~36k of each on SQLite where ~400 touched the file. The cache records already say who changed PATH (their diff is against the primary parent, so unlisted means byte-equal there): untouched ancestors inherit the parent's content pointer, the engine copies the parent's origins on pointer-identity, and the LCS trims the common prefix/suffix before its O(n*m) table.

Unfinishable on SQLite before; 0.5-1.2s typical, 57s for a 15k-line heavily-edited file (the multi-hunk quadratic middle remains — a real diff core is the named follow-up). Attribution of a repeated line between equally-valid origins can shift, as any LCS tiebreak may.

zit#172 check-in: 22bdf84fd3 user: dmestas tags: trunk