From 7842b48e60cd54be0e5f248563821a766590b0f0 Mon Sep 17 00:00:00 2001
From: Hermes Agent <hermes@localhost>
Date: Wed, 12 Aug 2026 05:45:02 +0000
Subject: Prevent archive overwrite races

---
 src/archive.rs | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

(limited to 'src/archive.rs')

diff --git a/src/archive.rs b/src/archive.rs
index ad424c4..c0a2195 100644
--- a/src/archive.rs
+++ b/src/archive.rs
@@ -27,6 +27,9 @@ impl NativeTarWriter {
 
         let output = output.as_ref();
         reject_output_inside_rootfs(rootfs, output)?;
+        if output.exists() {
+            bail!("archive output already exists; refusing to overwrite it: {}", output.display());
+        }
         let temporary = temporary_output_path(output)?;
         let result = (|| {
             let file = OpenOptions::new()
@@ -39,13 +42,18 @@ impl NativeTarWriter {
             archive
                 .finish()
                 .with_context(|| format!("finish archive {}", temporary.display()))?;
-            fs::rename(&temporary, output).with_context(|| {
+            // `rename` replaces an existing destination on Unix. Publishing via
+            // a hard link instead gives this same-directory temporary file an
+            // atomic no-replace final name.
+            fs::hard_link(&temporary, output).with_context(|| {
                 format!(
                     "publish completed archive {} as {}",
                     temporary.display(),
                     output.display()
                 )
-            })
+            })?;
+            fs::remove_file(&temporary)
+                .with_context(|| format!("remove temporary archive {}", temporary.display()))
         })();
         if result.is_err() {
             let _ = fs::remove_file(&temporary);
-- 
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