feat(diff): apply and revert hunks, lines and files from outside the working tree

crates/rgitui_diff/Cargo.toml

@@ -15,6 +15,9 @@ rgitui_ui.workspace = true
 rgitui_git.workspace = true
 rgitui_settings.workspace = true
 anyhow.workspace = true
+# Only for parsing a hex OID out of a `DiffSource` when building the tree pair
+# an apply/revert patch comes from.
+git2.workspace = true
 log.workspace = true
 syntect = { version = "5.3", default-features = false, features = ["default-fancy"] }
 

crates/rgitui_git/src/project/mod.rs

@@ -13,6 +13,7 @@ mod refresh;
 mod search;
 mod submodule;
 mod watcher;
+mod worktree_patch;
 
 use anyhow::{Context as _, Result};
 use git2::{Repository, StatusOptions};
@@ -79,6 +80,11 @@ pub use submodule::{
     compute_submodules, submodule_init, submodule_init_all, submodule_update, submodule_update_all,
     SubmoduleInfo,
 };
+pub use worktree_patch::{
+    apply_worktree_patch, restore_worktree_files, snapshots_fit_undo_stack,
+    WorktreeFilePermissions, WorktreeFileSnapshot, WorktreeFileState, WorktreePatchDirection,
+    WorktreePatchOutcome, WorktreePatchScope, WorktreePatchSource, MAX_UNDO_SNAPSHOT_BYTES,
+};
 
 fn parse_remote_tracking_ref(name: &str) -> Option<(String, String)> {
     let trimmed = name.strip_prefix("refs/remotes/").unwrap_or(name);
@@ -256,6 +262,18 @@ pub enum GitProjectEvent {
     /// Emitted after ahead/behind for all branches has been recomputed in the background.
     AheadBehindRefreshed,
     OperationUpdated(GitOperationUpdate),
+    /// An apply/revert rewrote working-tree files on disk. Carries what those
+    /// files held beforehand, which is the only record of it: the previous
+    /// contents are not recoverable from git state.
+    WorktreePatchApplied {
+        /// Undo label, e.g. "Applied hunk 2 of src/main.rs from a1b2c3d".
+        label: String,
+        snapshots: Vec<worktree_patch::WorktreeFileSnapshot>,
+        /// Repository entity that started the asynchronous mutation.
+        repo_path: PathBuf,
+        /// Effective worktree captured when the operation started.
+        worktree_path: PathBuf,
+    },
 }
 
 /// The core Git project state holder.