line-by-line authorship
Git blame, and a way back to the commit.
Blame answers a narrow question well: who last touched this line, and in which commit. The useful part is what you do next, which is read that commit.
From a line to its commit
Every line carries its commit, and every commit is one click from the history graph, where you can see what else it changed and why. Blame on its own tells you a name; blame that leads into the history tells you a reason.
It says when it cannot answer
A binary file cannot be blamed line by line, and FluxGit says exactly that rather than showing an empty panel. Very large outputs are truncated, and the panel tells you how many lines it is showing rather than quietly cutting the rest. A tool that pretends to have an answer is worse than one that admits the limit.