Replace gix with configurable libgit2 diffs

src/app/view/preferences.rs

@@ -183,6 +183,65 @@ impl App {
             ]
             .spacing(10),
         );
+        let git_group = preference_group(
+            PreferenceSection::Git,
+            "GIT DIFFS",
+            column![
+                row![
+                    hint(
+                        text("Algorithm").size(13).width(Length::Fill),
+                        "Default uses libgit2's Myers diff. Patience favors unique matching lines; Minimal spends more time finding the smallest edit script.",
+                    ),
+                    pick_list(
+                        &GIT_DIFF_ALGORITHMS[..],
+                        Some(self.preference_draft.git_diff_algorithm),
+                        Message::PreferenceGitDiffAlgorithmChanged,
+                    )
+                    .width(240),
+                ]
+                .spacing(12)
+                .align_y(Alignment::Center),
+                preference_input_row(
+                    "Context lines",
+                    "Unchanged lines shown before and after each changed block. libgit2 defaults to 3.",
+                    text_input("3", &self.preference_draft.git_context_lines)
+                        .on_input(Message::PreferenceGitContextLinesChanged),
+                ),
+                preference_input_row(
+                    "Interhunk lines",
+                    "Merge nearby changed blocks when no more than this many unchanged lines separate them. Zero keeps libgit2's default separation.",
+                    text_input("0", &self.preference_draft.git_interhunk_lines)
+                        .on_input(Message::PreferenceGitInterhunkLinesChanged),
+                ),
+                row![
+                    hint(
+                        text("Whitespace").size(13).width(Length::Fill),
+                        "Controls which whitespace-only edits libgit2 omits from the displayed diff.",
+                    ),
+                    pick_list(
+                        &GIT_DIFF_WHITESPACE_MODES[..],
+                        Some(self.preference_draft.git_whitespace),
+                        Message::PreferenceGitWhitespaceChanged,
+                    )
+                    .width(240),
+                ]
+                .spacing(12)
+                .align_y(Alignment::Center),
+                hint(
+                    checkbox(self.preference_draft.git_indent_heuristic)
+                        .label("Use indentation heuristic")
+                        .on_toggle(Message::PreferenceGitIndentHeuristicChanged),
+                    "Shift ambiguous hunk boundaries toward indentation changes, which usually makes source-code diffs easier to read.",
+                ),
+                hint(
+                    checkbox(self.preference_draft.git_ignore_blank_lines)
+                        .label("Ignore blank-line changes")
+                        .on_toggle(Message::PreferenceGitIgnoreBlankLinesChanged),
+                    "Hide hunks whose changed lines are all blank.",
+                ),
+            ]
+            .spacing(10),
+        );
         let generation_group = preference_group(
             PreferenceSection::Generation,
             "GENERATION",
@@ -580,6 +639,7 @@ impl App {
             model_group,
             endpoint_group,
             dev_brain_group,
+            git_group,
             generation_group,
             execution_group,
             acceleration_group,