diff --git a/Cargo.lock b/Cargo.lock
index fbbc4a49c2..04a2683459 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -379,6 +379,16 @@ version = "0.2.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "28dea519a9695b9977216879a3ebfddf92f1c08c05d984f8996aecd6ecdc811d"
 
+[[package]]
+name = "filetime"
+version = "0.2.29"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c287a33c7f0a620c38e641e7f60827713987b3c0f26e8ddc9462cc69cf75759"
+dependencies = [
+ "cfg-if",
+ "libc",
+]
+
 [[package]]
 name = "find-msvc-tools"
 version = "0.1.5"
@@ -861,6 +871,7 @@ dependencies = [
  "ansi-to-tui",
  "anyhow",
  "blake3",
+ "filetime",
  "globset",
  "ignore",
  "libc",
diff --git a/Cargo.toml b/Cargo.toml
index bf4634cea9..59a194fc97 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -32,6 +32,7 @@ tui = ["ratatui", "ansi-to-tui", "strip-ansi-escapes"]
 [dependencies]
 anyhow = "1"
 blake3 = "1"
+filetime = "0.2"
 globset = "0.4"
 libc = "0.2"
 ignore = "0.4"
diff --git a/src/cook/package.rs b/src/cook/package.rs
index 3b7d42a62f..7a1079a53b 100644
--- a/src/cook/package.rs
+++ b/src/cook/package.rs
@@ -81,6 +81,9 @@ pub fn package(
             .map_err(|err| format!("failed to create pkgar archive: {:?}", err))?;
         }
 
+        // T1.1: content-hash stability — see preserve_mtime_if_content_unchanged
+        preserve_mtime_if_content_unchanged(&stage_dir, &package_file, logger);
+
         let deps = if package.is_some() {
             BTreeSet::from([name.with_prefix(PackagePrefix::Any)])
         } else {
@@ -121,6 +124,87 @@ pub fn package(
     Ok(())
 }
 
+/// T1.1 — content-hash stability check.
+///
+/// Hashes the staged sysroot using BLAKE3 (sorted paths → deterministic
+/// regardless of filesystem ordering). Compares against the previous build's
+/// fingerprint. If identical, restores the previous `stage.pkgar` mtime on
+/// the new pkgar so dependents do not see a "changed" timestamp and skip
+/// their own rebuilds.
+///
+/// The fingerprint is stored next to the pkgar as `<name>.pkgar.fingerprint`
+/// so it survives across `repo clean` (no, it does not — but it survives
+/// ordinary rebuilds because the pkgar itself persists until next clean).
+fn preserve_mtime_if_content_unchanged(
+    stage_dir: &Path,
+    package_file: &Path,
+    logger: &PtyOut,
+) {
+    let Some(new_fp) = compute_stage_fingerprint(stage_dir) else {
+        return;
+    };
+    let fp_path = package_file.with_extension("pkgar.fingerprint");
+    let Ok(prev_fp) = std::fs::read_to_string(&fp_path) else {
+        // No previous fingerprint — record and return.
+        let _ = std::fs::write(&fp_path, &new_fp);
+        return;
+    };
+    if prev_fp.trim() != new_fp {
+        let _ = std::fs::write(&fp_path, &new_fp);
+        return;
+    }
+    let meta = match std::fs::metadata(package_file) {
+        Ok(m) => m,
+        Err(_) => return,
+    };
+    let mtime = match meta.modified() {
+        Ok(t) => t,
+        Err(_) => return,
+    };
+    let ft = match mtime.duration_since(std::time::UNIX_EPOCH) {
+        Ok(d) => filetime::FileTime::from_unix_time(d.as_secs() as i64, d.subsec_nanos()),
+        Err(_) => return,
+    };
+    if filetime::set_file_mtime(package_file, ft).is_ok() {
+        log_to_pty!(
+            logger,
+            "DEBUG: T1.1 preserved pkgar mtime (content unchanged): {}",
+            package_file.display()
+        );
+    }
+}
+
+fn compute_stage_fingerprint(stage_dir: &Path) -> Option<String> {
+    use std::collections::BTreeMap;
+    if !stage_dir.is_dir() {
+        return None;
+    }
+    let mut entries: BTreeMap<PathBuf, blake3::Hash> = BTreeMap::new();
+    let walker = walkdir::WalkDir::new(stage_dir)
+        .follow_links(false)
+        .into_iter()
+        .filter_map(Result::ok);
+    for entry in walker {
+        let path = entry.path();
+        if !entry.file_type().is_file() {
+            continue;
+        }
+        let Ok(bytes) = std::fs::read(path) else {
+            continue;
+        };
+        let rel = path.strip_prefix(stage_dir).unwrap_or(path).to_path_buf();
+        entries.insert(rel, blake3::hash(&bytes));
+    }
+    let mut hasher = blake3::Hasher::new();
+    for (rel, h) in &entries {
+        hasher.update(rel.to_string_lossy().as_bytes());
+        hasher.update(b"\0");
+        hasher.update(h.as_bytes());
+        hasher.update(b"\n");
+    }
+    Some(hasher.finalize().to_hex().to_string())
+}
+
 pub fn package_toml(
     toml_path: PathBuf,
     recipe: &CookRecipe,