fix(safe-paths): unlink symlinks and create files as the customer, never as root

drop_symlink and the logs/ symlink sweep now unlink AS THE CUSTOMER, and
user_touch no longer falls back to a root chown -h (a parent dir swapped for a
symlink between check and use could still redirect a root path operation).
A root-owned leftover error_log is fixed by the existing chown -R, which never
follows symlinks. Every operation these helpers perform is now safe even if the
customer races it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/safe-paths.sh

@@ -27,19 +27,20 @@ as_user() {
   fi
 }
 
-# drop_symlink PATH : if PATH is a symlink, unlink it (rm on a symlink never
-# touches the target) and log it.
+# drop_symlink PATH : if PATH is a symlink, unlink it and log it. The unlink
+# runs AS THE CUSTOMER: if a parent dir is swapped for a symlink between the
+# check and the rm, the customer can only unlink what they could already.
 drop_symlink() {
   if [ -L "$1" ]; then
-    echo "entrypoint: SECURITY: $1 was a symlink to '$(readlink "$1")' - removed" >&2
-    rm -f -- "$1"
+    echo "entrypoint: SECURITY: $1 was a symlink to '$(readlink "$1")' - removing" >&2
+    as_user rm -f -- "$1" || echo "entrypoint: WARNING: could not remove symlink $1" >&2
   fi
 }
 
 # secure_home : run once, right after adduser, before anything else touches
 # /home/$user.
 secure_home() {
-  local h="/home/$user" d
+  local h="/home/$user"
   if [ -L "$h" ] || [ ! -d "$h" ]; then
     echo "entrypoint: FATAL: $h is not a real directory (symlink or missing) - refusing to start" >&2
     exit 1
@@ -49,11 +50,10 @@ secure_home() {
   drop_symlink "$h/logs"
   # public_html may legitimately be a symlink (release-dir deploys); it is left
   # alone and every root-side operation on it runs as the customer instead.
-  if [ -d "$h/logs" ]; then
-    # find without -L never follows symlinks (start path verified real above).
-    find "$h/logs" -xdev -type l -print0 2>/dev/null | while IFS= read -r -d '' d; do
-      drop_symlink "$d"
-    done
+  if [ -d "$h/logs" ] && [ ! -L "$h/logs" ]; then
+    # As the customer, find without -L never follows symlinks; -delete unlinks.
+    as_user find "$h/logs" -xdev -type l \
+      -printf 'entrypoint: SECURITY: %p was a symlink to %l - removed\n' -delete >&2 || true
   fi
 }
 
@@ -62,12 +62,13 @@ user_mkdir() {
   as_user mkdir -p -- "$@"
 }
 
-# user_touch FILE : create FILE as the customer. If it already exists owned by
-# someone else (root-created by an older image), fix ownership with chown -h,
-# which never follows a symlink; a symlink there is dropped first.
+# user_touch FILE : create FILE as the customer (a symlink there is dropped
+# first). Root never touches/chowns it: if it already exists root-owned (left by
+# an older image) the touch fails quietly and the entrypoint's chown -R, which
+# never follows symlinks, fixes the owner.
 user_touch() {
   drop_symlink "$1"
-  as_user touch -- "$1" 2>/dev/null || chown -h "$user:$user" -- "$1" 2>/dev/null || true
+  as_user touch -- "$1" 2>/dev/null || true
 }
 
 # load_user_crontab : install /home/$user/crontab, read AS THE CUSTOMER. Root