diff --git a/.claude/skills/new-module/SKILL.md b/.claude/skills/new-module/SKILL.md
index 5473176..71dff26 100644
--- a/.claude/skills/new-module/SKILL.md
+++ b/.claude/skills/new-module/SKILL.md
@@ -102,6 +102,10 @@ There is **no `--dry-run` and no `--check-mode`** — to sanity-check config/pat
   `du -sh /opt/psi/MX/<name>/<version>` from a second shell; don't kill a healthy build.
 - modbuild runs hooks with `pipefail` + `nounset`: `yes | cmd` fails (SIGPIPE) — use
   `printf 'y\ny\n' | cmd`.
+- **Never `cp -a` / `cp -p` into `$PREFIX`**: chown is refused on `/opt/psi`, so every
+  file logs `failed to preserve ownership ... Permission denied` and cp exits non-zero
+  (olex2 2026-10: 12k-line log, die-guard aborted a healthy copy). Use
+  `cp -r --preserve=mode,timestamps,links src/. "$PREFIX"/` (or tar pipe / `install`).
 - modbuild has **no errexit in hooks**: a failed command scrolls by and the build still
   prints "done", installing the modulefile over a broken PREFIX. Guard every critical
   hook step with `|| std::die 42 "<what and how to recover>"` and end `install` with an
diff --git a/olex2/build b/olex2/build
index 193b429..b55ec68 100755
--- a/olex2/build
+++ b/olex2/build
@@ -38,7 +38,11 @@ pbuild::install() {
     local -r src="${SRC_DIR}/olex2"
 
     # 1. vendor tree, flat into $PREFIX (= BaseDir). Slow on /opt/psi: 12k files.
-    cp -a "${src}/." "${PREFIX}/" || std::die 42 "olex2: copying the vendor tree into ${PREFIX} failed"
+    #    NOT `cp -a`: on /opt/psi chown is refused, so -a ends with thousands of
+    #    "failed to preserve ownership ... Permission denied" and a non-zero exit
+    #    (that killed the first build). Keep mode/timestamps/links only.
+    cp -r --preserve=mode,timestamps,links "${src}/." "${PREFIX}/" || \
+        std::die 42 "olex2: copying the vendor tree into ${PREFIX} failed"
 
     # 2. zip loses nothing, but make sure the ELF binaries are executable and
     #    everything is world-readable on the shared install