Write final.patch (base_sha → HEAD) to logs_root after pipeline completes

Per-stage diff.patch files only capture incremental changes between
checkpoints. This adds a comprehensive final.patch covering all changes
from the run's base SHA to the final HEAD, written to logs_root for all
execution environments. Especially important for Daytona where the
sandbox is destroyed after the run.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

crates/arc-attractor/src/engine.rs

@@ -1211,6 +1211,21 @@ impl PipelineEngine {
             final_git_commit_sha: last_git_sha.clone(),
         });
 
+        // Write final.patch: comprehensive diff from base_sha to HEAD
+        if let (Some(ref mode), Some(ref base)) = (&config.git_checkpoint, &config.base_sha) {
+            let patch = match mode {
+                GitCheckpointMode::Host(work_dir) => {
+                    git_diff_host(work_dir.clone(), base.clone()).await
+                }
+                GitCheckpointMode::Remote => {
+                    git_diff_remote(&*self.services.execution_env, base).await
+                }
+            };
+            if let Some(patch) = patch {
+                let _ = std::fs::write(config.logs_root.join("final.patch"), patch);
+            }
+        }
+
         // Return last outcome, or success if no outcomes recorded
         let last_outcome = node_outcomes
             .get(completed_nodes.last().unwrap_or(&String::new()))

crates/arc-attractor/tests/daytona_integration.rs

@@ -474,6 +474,12 @@ async fn daytona_git_checkpoint_remote_emits_events() {
         "checkpoint should have git_commit_sha"
     );
 
+    // Assert final.patch exists and contains changes from the run
+    let final_patch = dir.path().join("final.patch");
+    assert!(final_patch.exists(), "final.patch should exist in logs_root");
+    let patch_content = std::fs::read_to_string(&final_patch).unwrap();
+    assert!(!patch_content.is_empty(), "final.patch should not be empty");
+
     env.cleanup().await.unwrap();
 }
 

crates/arc-attractor/tests/integration.rs

@@ -8395,6 +8395,12 @@ async fn git_checkpoint_host_emits_events_and_diff_patch() {
         "checkpoint should have git_commit_sha"
     );
 
+    // 9. Assert final.patch exists and contains the changes
+    let final_patch = logs_dir.path().join("final.patch");
+    assert!(final_patch.exists(), "final.patch should exist in logs_root");
+    let patch_content = std::fs::read_to_string(&final_patch).unwrap();
+    assert!(patch_content.contains("hello.txt"), "final.patch should contain hello.txt changes");
+
     // Cleanup worktree
     let _ = std::process::Command::new("git")
         .args(["worktree", "remove", "--force"])