diff --git a/scripts/sync-marketplace-mirror.sh b/scripts/sync-marketplace-mirror.sh
index c61d709..225ba57 100755
--- a/scripts/sync-marketplace-mirror.sh
+++ b/scripts/sync-marketplace-mirror.sh
@@ -12,7 +12,18 @@ set -euo pipefail
 # script keeps that legacy mirror byte-identical to .claude-plugin/marketplace.json
 # instead of letting it silently drift (see issue #90 comment thread).
 
-REPO_ROOT="$(git rev-parse --show-toplevel 2>/dev/null || pwd)"
+# Hard error, not a `|| pwd` fallback. Every path this script touches hangs off
+# REPO_ROOT, and both of its exits-0 paths are "the files agree" or "neither file
+# exists" -- so a REPO_ROOT pointing somewhere that is not this repo reports "no
+# drift" over a tree it never looked at. Run `--check` from an empty directory
+# outside any worktree and the fallback made that the literal outcome: rev-parse
+# failed, REPO_ROOT became $PWD, neither file was there, exit 0. Refusing to guess
+# is the only answer that cannot be silently wrong; the `-f "$DST"` branch below
+# covers a genuinely stale mirror, which is a different condition.
+if ! REPO_ROOT="$(git rev-parse --show-toplevel 2>/dev/null)" || [[ -z "$REPO_ROOT" ]]; then
+  echo "Error: not inside a git worktree -- cannot locate the repository root, and guessing \$PWD would let --check report \"no drift\" over a tree it never inspected. Run this from within the repository." >&2
+  exit 1
+fi
 SRC="$REPO_ROOT/.claude-plugin/marketplace.json"
 DST="$REPO_ROOT/.github/plugin/marketplace.json"
 
@@ -32,9 +43,9 @@ if [[ ! -f "$SRC" ]]; then
   # A missing source with a surviving mirror is drift, not absence: the mirror
   # can only be stale (nothing is left for it to be byte-identical to), which is
   # precisely the silent divergence this script exists to prevent. Exiting 0
-  # here would report "no drift" over a mirror of a file that no longer exists,
-  # and would also swallow the case where REPO_ROOT resolved to the wrong tree —
-  # `git rev-parse --show-toplevel` falls back to `pwd` outside a worktree.
+  # here would report "no drift" over a mirror of a file that no longer exists.
+  # (An unresolvable REPO_ROOT is handled above and is a hard error; this branch
+  # is only about a source file that is genuinely gone from a real worktree.)
   # scripts/sync-plugin-content.sh --check --all already errors on the same
   # condition ("requires .../marketplace.json"); this matches it.
   # Neither file present stays a genuine no-op: nothing to mirror, nothing stale.
diff --git a/scripts/sync-plugin-content.sh b/scripts/sync-plugin-content.sh
index 0cd1ee2..44aa705 100755
--- a/scripts/sync-plugin-content.sh
+++ b/scripts/sync-plugin-content.sh
@@ -142,6 +142,23 @@ FAIL=0
 SCRATCH_ROOT="$(mktemp -d)"
 trap 'rm -rf "$SCRATCH_ROOT"' EXIT
 
+# The manifest comparison in check_path_modes needs octal permission bits, and
+# GNU coreutils and BSD/macOS stat disagree on both the flag and the format
+# specifier. Probe once at startup against a path known to exist rather than
+# branching on `uname` (which says nothing about which coreutils is installed --
+# GNU stat is perfectly common on macOS via Homebrew).
+declare -a STAT_MODE_ARGS=()
+if [[ "$(stat -c '%a' "$SCRIPT_DIR" 2>/dev/null)" =~ ^[0-7]+$ ]]; then
+  STAT_MODE_ARGS=(-c '%a')
+elif [[ "$(stat -f '%Lp' "$SCRIPT_DIR" 2>/dev/null)" =~ ^[0-7]+$ ]]; then
+  STAT_MODE_ARGS=(-f '%Lp')
+else
+  # Hard error rather than degrading to a no-mode manifest: silently checking
+  # less than advertised is the exact failure mode this gate exists to prevent.
+  echo "Error: cannot read octal file modes -- neither \`stat -c '%a'\` (GNU coreutils) nor \`stat -f '%Lp'\` (BSD/macOS) works here" >&2
+  exit 1
+fi
+
 if [[ "$ALL" -eq 1 ]]; then
   # Derives the plugin list from marketplace.json via the shared
   # list_marketplace_local_plugins helper (scripts/lib/marketplace-plugins.sh),
@@ -154,10 +171,25 @@ if [[ "$ALL" -eq 1 ]]; then
     echo "Error: --all requires $MARKETPLACE" >&2
     exit 1
   fi
+  # Called from this shell, NOT from inside the `< <(...)` below -- that process
+  # substitution is its own subshell, so a `set -e` abort or a jq parse failure in
+  # there kills only the subshell and the `while read` loop simply gets no input.
+  # An unparseable marketplace.json then reads exactly like "declares no plugins",
+  # plugin_dirs comes back empty, batch_run dispatches nothing, and --check --all
+  # exits 0 having verified nothing at all (see the floor below).
+  assert_marketplace_manifest_usable "$MARKETPLACE"
   declare -a plugin_dirs=()
   while IFS=$'\t' read -r _name plugin_dir; do
     plugin_dirs+=("$plugin_dir")
   done < <(list_marketplace_local_plugins "$REPO_ROOT" "$MARKETPLACE")
+  # Floor: --all is a gate whose work list comes from a GENERATED file, so an
+  # empty derived set is drift, not a pass -- regenerating marketplace.json badly
+  # would otherwise silence the very hook that guards it. assert_... above rejects
+  # the malformed shapes; this rejects the well-formed-but-empty one.
+  if [[ ${#plugin_dirs[@]} -eq 0 ]]; then
+    echo "Error: $MARKETPLACE declares no local (string-source) plugin entries -- --all would check nothing and report success. Expected at least one; recompile it with \`apm pack\` if it is stale." >&2
+    exit 1
+  fi
 else
   declare -a plugin_dirs=("$@")
 fi
@@ -165,9 +197,24 @@ fi
 # Fail fast on a basename collision rather than letting two plugin_dir arguments
 # silently share (and corrupt) the same $name.log/$name.status/$name.checkcopy
 # scratch paths below.
+#
+# The same loop rejects `.` and `..`, because every scratch path here is built by
+# pasting this basename onto $SCRATCH_ROOT. `basename ..` is `..`, so
+# "$SCRATCH_ROOT/$name" resolves to $SCRATCH_ROOT's PARENT -- apm pack then writes
+# its bundle into a directory this script neither owns nor cleans up (the EXIT
+# trap only removes $SCRATCH_ROOT itself), and sync_one's
+# `find "$scratch" -mindepth 1 -maxdepth 1 -type d | head -1` picks whatever
+# unrelated directory readdir happens to hand back first as the "bundle" -- whose
+# agents/ and skills/ a real sync then cp -a's into the plugin root, after an
+# rm -rf. The collision check below cannot catch this: a single `..` argument
+# collides with nothing.
 declare -a seen_names=()
 for plugin_dir in ${plugin_dirs[@]+"${plugin_dirs[@]}"}; do
   name="$(basename "${plugin_dir%/}")"
+  if [[ "$name" == "." || "$name" == ".." ]]; then
+    echo "Error: plugin dir '$plugin_dir' has basename '$name' -- scratch paths built from it would escape the scratch root. Pass the plugin directory by name, not by a relative traversal." >&2
+    exit 1
+  fi
   for seen in ${seen_names[@]+"${seen_names[@]}"}; do
     if [[ "$seen" == "$name" ]]; then
       echo "Error: duplicate plugin basename '$name' among arguments -- scratch paths would collide" >&2
@@ -190,7 +237,13 @@ normalize_trailing_newline() {
 # that rule anywhere in this script.
 sync_dir() {
   local target_dir="$1" bundle_dir="$2" d="$3"
-  local src="$bundle_dir/$d" dst="$target_dir/$d"
+  # ${target_dir:?} for the same reason sync_hooks_json spells it out: `set -u`
+  # aborts on an UNSET variable but not an empty one, and an empty $target_dir
+  # would make the rm -rf calls below `rm -rf /agents`, `/skills`, `/commands`,
+  # `/instructions`, `/extensions`. Unreachable from today's two call sites
+  # (both pass either a `[[ -d ]]`-validated plugin_dir or a scratch path), but
+  # the guard costs nothing and the next caller added here gets it for free.
+  local src="$bundle_dir/$d" dst="${target_dir:?}/$d"
 
   if [[ -d "$src" ]]; then
     rm -rf "$dst"
@@ -232,8 +285,9 @@ sync_hooks_json() {
   #
   # ${target_dir:?} rather than a bare expansion: `set -u` aborts on an UNSET
   # variable but not an empty one, and an empty $target_dir would make this
-  # `rm -rf /hooks`. The other rm -rf calls here take a $dst built by their
-  # caller; this one is the only place a bare parameter is the whole prefix.
+  # `rm -rf /hooks`. sync_dir above builds its own $dst from the same
+  # caller-supplied parameter and carries the identical guard for the identical
+  # reason -- neither function is special here.
   rm -rf "${target_dir:?}/$HOOKS_DIR_REL"
 
   if [[ -f "$src" ]]; then
@@ -287,28 +341,53 @@ check_file() {
   fi
 }
 
-# Prints "<kind> <relative-path>" for every entry under the given relative paths.
-# `find` is used rather than a stat(1) call because stat's flags for mode
-# formatting are incompatible between GNU and BSD/macOS.
+# Prints "<kind> <octal-mode> <relative-path>" for every entry under the given
+# relative paths. `find` walks; $STAT_MODE_ARGS (probed once at startup) reads the
+# mode, because stat's flags for mode formatting are incompatible between GNU and
+# BSD/macOS.
+#
+# Full permission bits on FILES, not just the exec bit: an earlier revision emitted
+# a bare `exec`/`file` kind, so `chmod 444` on a mirrored SKILL.md left --check at
+# exit 0 while a real sync restored 644 -- check and sync disagreeing again, in the
+# same shape the exec-bit case already proved. Git tracks only the exec bit, so this
+# cannot arrive via a clone, but the gate's contract is that it agrees with a real
+# sync about everything a real sync writes.
+#
+# DIRECTORIES record no mode, deliberately. Nothing in this script ever sets one:
+# the expected side's directories come from `mkdir -p` and `cp -a` under the
+# running process's umask, the real side's from git checkout under whatever umask
+# cloned the repo, and git tracks no directory mode at any point in between. So the
+# comparison would report the runner's umask rather than any property of the
+# mirror -- a repo cloned at umask 002 and checked at 022 would fail this gate on
+# every directory with nothing wrong. Verified concretely: extracting this repo
+# with `git archive | tar -x` (which restores 0775/0664 when run as root) makes a
+# --check against the extracted tree report drift on every mirrored directory,
+# while the same check against the real 0755 tree is silent. Mirrored FILES do not
+# have this problem: both sides trace to the same checkout, since the expected side
+# is `cp -a`'d from a bundle apm built out of the same .apm/ files.
 path_manifest() {
   local root="$1"
   shift
-  local rel f kind
+  local rel f kind mode
   for rel in "$@"; do
     if [[ ! -e "$root/$rel" ]] && [[ ! -L "$root/$rel" ]]; then
       continue
     fi
     find "$root/$rel" -print 2>/dev/null | LC_ALL=C sort | while IFS= read -r f; do
       if [[ -L "$f" ]]; then
+        # A symlink's own lstat mode is 0777 on Linux and 0755 on macOS and is
+        # not something either side controls -- the type difference is the whole
+        # signal here, so record no mode for it.
         kind="symlink"
+        mode="-"
       elif [[ -d "$f" ]]; then
         kind="dir"
-      elif [[ -x "$f" ]]; then
-        kind="exec"
+        mode="-"
       else
         kind="file"
+        mode="$(stat "${STAT_MODE_ARGS[@]}" "$f")"
       fi
-      printf '%s %s\n' "$kind" "${f#"$root"/}"
+      printf '%s %s %s\n' "$kind" "$mode" "${f#"$root"/}"
     done || true
   done
 }
@@ -317,7 +396,7 @@ path_manifest() {
 # entirely. So `chmod -x` on a mirrored script, or swapping a mirrored file for a
 # symlink to identical content, both leave --check at exit 0 while a real sync
 # silently repairs them -- check and sync disagreeing, which is the one thing this
-# gate exists to prevent. Compare an explicit type+exec-bit manifest as well.
+# gate exists to prevent. Compare an explicit type+permission manifest as well.
 #
 # The manifest is a full recursive listing, so it is also what makes an entry that
 # exists on only one side visible. That is the sole coverage the generated hooks/
@@ -342,6 +421,25 @@ check_path_modes() {
   rm -f "$expected" "$actual"
 }
 
+# Sets `mcpServers` on the generated Copilot manifest to the STRING ".mcp.json" --
+# the path form of the field, not the resolved server objects. Copilot's schema
+# types the field "string or object -- MCP server config path or inline
+# definitions" (plugins/kyberforge/docs/research/docs/github-copilot-plugins/
+# configuration.md), so both are valid there; only one of them is safe.
+#
+# An earlier revision inlined the objects with
+# `jq --slurpfile mcp '.mcpServers = $mcp[0].mcpServers'`. That copies .mcp.json
+# verbatim into a committed, marketplace-distributed file, bypassing apm's own
+# _sanitize_mcp_servers() (apm_cli/core/plugin_manifest.py), which drops
+# env/environment/headers/authorization and any key matching
+# token/secret/password/credential/apikey/key at any depth before writing the
+# Claude manifest. Proven with a fixture: an `env` block holding a token-shaped
+# value produced a sanitized .claude-plugin/plugin.json and a
+# .github/plugin/plugin.json carrying the live value. A path reference cannot
+# carry a secret at all -- the manifest names a file and the host resolves it at
+# load time -- and it preserves the ${VAR} indirection apm documents as the
+# posture for MCP secrets, rather than stripping it. See ADR-0017's 2026-08-14
+# amendment.
 reinject_mcp_servers() {
   local plugin_dir="$1" target_dir="$2"
   local mcp_src="$plugin_dir/.mcp.json" dst="$target_dir/.github/plugin/plugin.json"
@@ -350,14 +448,27 @@ reinject_mcp_servers() {
 
   # Match apm's own Claude-ecosystem plugin.json builder: mcpServers is omitted
   # entirely when the plugin declares none, not written out as an empty object.
+  # A plugin whose .mcp.json is `{"mcpServers": {}}` gets no key at all -- not a
+  # ".mcp.json" pointer at an empty file.
   local count
   count="$(jq '(.mcpServers // {}) | length' "$mcp_src")"
   [[ "$count" -gt 0 ]] || return 0
 
   local tmp
   tmp="$(mktemp)"
-  jq --slurpfile mcp "$mcp_src" '.mcpServers = $mcp[0].mcpServers' "$dst" >"$tmp"
-  mv "$tmp" "$dst"
+  jq '.mcpServers = ".mcp.json"' "$dst" >"$tmp"
+  # Write THROUGH the existing file rather than `mv`-ing the mktemp over it:
+  # mktemp creates 0600, and mv carries that mode onto a tracked, published
+  # manifest. Git records only the exec bit, so the demotion survived every
+  # commit and review unnoticed -- plugins/bin/.github/plugin/plugin.json really
+  # was 0600 on disk while its five siblings were 0644. Redirecting into $dst
+  # keeps its inode, owner and mode; the chmod then pins the mode of a file this
+  # script owns as generated output, so a fresh sync and a re-sync over a
+  # tampered tree converge on the same answer (and --check, which now carries
+  # this path in its mode manifest, can see when they would not).
+  cat "$tmp" >"$dst"
+  rm -f "$tmp"
+  chmod 644 "$dst"
 }
 
 # --check-only: diffs a freshly-regenerated manifest file (in the throwaway
@@ -465,7 +576,15 @@ sync_one() {
     # $HOOKS_DIR_REL, not $HOOKS_REL: the manifest comparison has to see the whole
     # generated directory (see check_path_modes), and listing it recursively already
     # covers hooks/hooks.json.
-    checked_paths=("${MIRROR_DIRS[@]}" "$HOOKS_DIR_REL" "$LEGACY_HOOKS_REL")
+    #
+    # .github/plugin/plugin.json is in the list even though sync_plugin_manifest
+    # below already diffs its CONTENT: that diff is content-only, so the mode
+    # reinject_mcp_servers writes was outside --check's manifest entirely and the
+    # 0600 demotion above went undetected for as long as it existed. Its sibling
+    # .claude-plugin/plugin.json is listed for the same reason -- nothing here
+    # writes its mode today, which is exactly the state worth pinning.
+    checked_paths=("${MIRROR_DIRS[@]}" "$HOOKS_DIR_REL" "$LEGACY_HOOKS_REL" \
+      ".claude-plugin/plugin.json" ".github/plugin/plugin.json")
     for d in "${MIRROR_DIRS[@]}"; do
       check_dir "$plugin_dir" "$pack_cwd" "$d"
     done
diff --git a/tests/test-sync-marketplace-mirror.sh b/tests/test-sync-marketplace-mirror.sh
index 4b10082..416ba13 100755
--- a/tests/test-sync-marketplace-mirror.sh
+++ b/tests/test-sync-marketplace-mirror.sh
@@ -255,6 +255,50 @@ else
   fail "an inherited GIT_DIR/GIT_WORK_TREE redirected the sync outside the fixture"
 fi
 
+# --- 13. Outside any git worktree, REPO_ROOT cannot be guessed: hard error ---
+# `git rev-parse --show-toplevel 2>/dev/null || pwd` used to fall back to $PWD.
+# Both of this script's exit-0 paths are "the two files agree" or "neither file
+# exists", so a REPO_ROOT that is not this repo reports "no drift" over a tree it
+# never inspected — run --check from an empty non-worktree directory and that was
+# the literal outcome. Case 2 above (a real worktree with no source file) still
+# exits 0; the difference is whether the tree was identified at all.
+#
+# GIT_CEILING_DIRECTORIES rather than trusting `mktemp -d` to land outside a
+# worktree: TMPDIR may itself sit inside one (the same hazard make_fixture's
+# header documents), in which case rev-parse would succeed and this case would
+# quietly test nothing. The ceiling stops git's upward walk at the fixture's
+# parent, and the precondition below asserts it actually did.
+echo ""
+echo "--- outside a git worktree, --check errors instead of guessing \$PWD ---"
+NOREPO_PARENT="$(mktemp -d)"; track "$NOREPO_PARENT"
+NOREPO_PARENT="$(cd "$NOREPO_PARENT" && pwd -P)"
+NOREPO="$NOREPO_PARENT/not-a-worktree"
+mkdir -p "$NOREPO"
+if (cd "$NOREPO" && env -u GIT_DIR -u GIT_WORK_TREE GIT_CEILING_DIRECTORIES="$NOREPO_PARENT" \
+    git rev-parse --show-toplevel > /dev/null 2>&1); then
+  fail "precondition: git rev-parse still resolves a worktree under the ceiling — this case would test nothing"
+else
+  for MODE in "--check" ""; do
+    RC13=0
+    OUT13="$( (cd "$NOREPO" && env -u GIT_DIR -u GIT_WORK_TREE \
+      GIT_CEILING_DIRECTORIES="$NOREPO_PARENT" bash "$SCRIPT" ${MODE:+"$MODE"}) 2>&1 )" || RC13=$?
+    case "$RC13:$OUT13" in
+      0:*)
+        fail "'${MODE:-real sync}' exited 0 outside a git worktree — it reported on a tree it never identified" ;;
+      *"not inside a git worktree"*)
+        pass "'${MODE:-real sync}' errors with a not-a-worktree message instead of falling back to \$PWD" ;;
+      *)
+        fail "'${MODE:-real sync}' failed for an unexpected reason (rc=$RC13): $OUT13" ;;
+    esac
+  done
+  # And it must not have written anything into the directory it refused to trust.
+  if [[ ! -e "$NOREPO/.github" ]]; then
+    pass "nothing is written into the unidentified directory"
+  else
+    fail "the script created files under a directory it could not identify as the repo root"
+  fi
+fi
+
 echo ""
 echo "Results: $PASS passed, $FAIL failed"
 [[ $FAIL -eq 0 ]]
diff --git a/tests/test-sync-plugin-content.sh b/tests/test-sync-plugin-content.sh
index a3bf90f..51faeed 100755
--- a/tests/test-sync-plugin-content.sh
+++ b/tests/test-sync-plugin-content.sh
@@ -301,15 +301,43 @@ else
   pass "rejects two plugin-dir arguments that share a basename"
 fi
 
-# --- 10. Real sync re-injects mcpServers that apm's Copilot builder strips ---
+# --- 10. Real sync re-injects mcpServers as a PATH that apm's Copilot builder strips ---
+# The payload is the string ".mcp.json", not the resolved server objects: Copilot's
+# schema types the field "string or object", and only the string form is incapable
+# of carrying a credential into a committed, published manifest (see case 23).
 echo ""
-echo "--- real sync re-injects mcpServers into .github/plugin/plugin.json ---"
+echo "--- real sync re-injects mcpServers into .github/plugin/plugin.json as a path ---"
 FIXTURE10="$(make_fixture_with_mcp '{"mcpServers":{"demo":{"command":"demo-server","type":"stdio"}}}')"; track "$FIXTURE10"
 bash "$SCRIPT" "$FIXTURE10" > /dev/null 2>&1
-if jq -e '.mcpServers.demo.command == "demo-server"' "$FIXTURE10/.github/plugin/plugin.json" > /dev/null 2>&1; then
-  pass "mcpServers from .mcp.json is present in .github/plugin/plugin.json after a real sync"
+if jq -e '.mcpServers == ".mcp.json"' "$FIXTURE10/.github/plugin/plugin.json" > /dev/null 2>&1; then
+  pass "mcpServers is the string \".mcp.json\" in .github/plugin/plugin.json after a real sync"
 else
-  fail "mcpServers was not re-injected into .github/plugin/plugin.json"
+  fail "mcpServers was not re-injected as the path \".mcp.json\" (got: $(jq -c '.mcpServers // "<absent>"' "$FIXTURE10/.github/plugin/plugin.json" 2>/dev/null))"
+fi
+# The inlined-object form is what leaked; assert it is gone, not merely that a
+# key exists. `jq -e '.mcpServers == ".mcp.json"'` above already implies this, but
+# a future refactor that emits an object again should fail on the reason, not just
+# on the shape.
+if jq -e '.mcpServers | type == "object"' "$FIXTURE10/.github/plugin/plugin.json" > /dev/null 2>&1; then
+  fail "mcpServers was inlined as an object — that is the form that copies .mcp.json verbatim into a published manifest"
+else
+  pass "mcpServers is not an inlined object"
+fi
+
+# --- 10b. .github/plugin/plugin.json is world-readable 0644, not mktemp's 0600 ---
+# reinject_mcp_servers used to build its replacement in a `mktemp` file (mode 0600)
+# and `mv` it over the manifest, carrying 0600 onto a tracked, published file. Git
+# records only the exec bit, so the demotion survived every commit unnoticed — this
+# repo's own plugins/bin/.github/plugin/plugin.json really was 0600 on disk while
+# its five siblings were 0644.
+echo ""
+echo "--- a real sync leaves .github/plugin/plugin.json at mode 644 ---"
+MODE10="$(stat -c '%a' "$FIXTURE10/.github/plugin/plugin.json" 2>/dev/null \
+  || stat -f '%Lp' "$FIXTURE10/.github/plugin/plugin.json" 2>/dev/null)"
+if [[ "$MODE10" == "644" ]]; then
+  pass "mcpServers re-injection leaves the manifest at 644"
+else
+  fail "mcpServers re-injection left .github/plugin/plugin.json at mode $MODE10, expected 644"
 fi
 
 # --- 11. An empty .mcp.json does not add a redundant mcpServers: {} ---
@@ -479,24 +507,38 @@ echo ""
 echo "--- --check reports all independent drifts in a single run ---"
 FIXTURE17="$(make_fixture)"; track "$FIXTURE17"
 bash "$SCRIPT" "$FIXTURE17" > /dev/null 2>&1
-printf 'tampered\n' >> "$FIXTURE17/agents/foo.agent.md"
-printf 'tampered\n' >> "$FIXTURE17/skills/hello/SKILL.md"
-printf 'tampered\n' >> "$FIXTURE17/commands/mycmd.md"
-printf 'tampered\n' >> "$FIXTURE17/instructions/style.instructions.md"
-mkdir -p "$FIXTURE17/hooks"
-printf '{"hooks": {"PreToolUse": [], "tampered": true}}\n' > "$FIXTURE17/hooks/hooks.json"
-CHECK17="$(bash "$SCRIPT" --check "$FIXTURE17" 2>&1 || true)"
-MISSED=""
-for CATEGORY_PATH in agents skills commands instructions hooks/hooks.json; do
-  case "$CHECK17" in
-    *"DRIFT $FIXTURE17/$CATEGORY_PATH"*) ;;
-    *) MISSED="$MISSED $CATEGORY_PATH" ;;
-  esac
+# Guarded like case 16's `[[ ! -f ... ]] || continue`, and for the same reason:
+# an unwritable path here makes `printf >>` fail, and under `set -e` that aborts
+# the whole script — no "Results:" line, and cases 18-22 never run at all. The
+# exit status is non-zero so the dispatcher does report FAILED, but the six lost
+# assertions are invisible and the only diagnostic is a bare shell error.
+MISSING17=""
+for CATEGORY_PATH in agents/foo.agent.md skills/hello/SKILL.md commands/mycmd.md \
+  instructions/style.instructions.md; do
+  [[ -f "$FIXTURE17/$CATEGORY_PATH" ]] || MISSING17="$MISSING17 $CATEGORY_PATH"
 done
-if [[ -z "$MISSED" ]]; then
-  pass "all five independent drifts are reported in one --check run"
+if [[ -n "$MISSING17" ]]; then
+  fail "sync did not mirror:$MISSING17 — cannot test multi-drift reporting"
 else
-  fail "--check stopped early — never reported drift for:$MISSED"
+  printf 'tampered\n' >> "$FIXTURE17/agents/foo.agent.md"
+  printf 'tampered\n' >> "$FIXTURE17/skills/hello/SKILL.md"
+  printf 'tampered\n' >> "$FIXTURE17/commands/mycmd.md"
+  printf 'tampered\n' >> "$FIXTURE17/instructions/style.instructions.md"
+  mkdir -p "$FIXTURE17/hooks"
+  printf '{"hooks": {"PreToolUse": [], "tampered": true}}\n' > "$FIXTURE17/hooks/hooks.json"
+  CHECK17="$(bash "$SCRIPT" --check "$FIXTURE17" 2>&1 || true)"
+  MISSED=""
+  for CATEGORY_PATH in agents skills commands instructions hooks/hooks.json; do
+    case "$CHECK17" in
+      *"DRIFT $FIXTURE17/$CATEGORY_PATH"*) ;;
+      *) MISSED="$MISSED $CATEGORY_PATH" ;;
+    esac
+  done
+  if [[ -z "$MISSED" ]]; then
+    pass "all five independent drifts are reported in one --check run"
+  else
+    fail "--check stopped early — never reported drift for:$MISSED"
+  fi
 fi
 
 # --- 18. --check sees a mode change on a mirrored executable ---
@@ -532,18 +574,24 @@ echo "--- --check detects a mirrored file swapped for a symlink ---"
 FIXTURE19="$(make_fixture)"; track "$FIXTURE19"
 bash "$SCRIPT" "$FIXTURE19" > /dev/null 2>&1
 SYMLINK_TARGET="$FIXTURE19/decoy-agent.md"
-cp "$FIXTURE19/agents/foo.agent.md" "$SYMLINK_TARGET"
-rm -f "$FIXTURE19/agents/foo.agent.md"
-ln -s "$SYMLINK_TARGET" "$FIXTURE19/agents/foo.agent.md"
-if bash "$SCRIPT" --check "$FIXTURE19" > /dev/null 2>&1; then
-  fail "no drift reported after replacing a mirrored file with a symlink to identical content"
+# Guarded for the same reason as cases 16 and 17: with the mirror absent the `cp`
+# below fails and `set -e` takes the rest of the suite down with it.
+if [[ ! -f "$FIXTURE19/agents/foo.agent.md" ]]; then
+  fail "sync did not mirror agents/foo.agent.md — cannot test the symlink-swap case"
 else
-  pass "a mirrored file replaced by a symlink is detected as drift"
-  bash "$SCRIPT" "$FIXTURE19" > /dev/null 2>&1
-  if [[ -f "$FIXTURE19/agents/foo.agent.md" ]] && [[ ! -L "$FIXTURE19/agents/foo.agent.md" ]]; then
-    pass "re-sync restores it to a regular file"
+  cp "$FIXTURE19/agents/foo.agent.md" "$SYMLINK_TARGET"
+  rm -f "$FIXTURE19/agents/foo.agent.md"
+  ln -s "$SYMLINK_TARGET" "$FIXTURE19/agents/foo.agent.md"
+  if bash "$SCRIPT" --check "$FIXTURE19" > /dev/null 2>&1; then
+    fail "no drift reported after replacing a mirrored file with a symlink to identical content"
   else
-    fail "re-sync did not restore the symlinked mirror entry to a regular file"
+    pass "a mirrored file replaced by a symlink is detected as drift"
+    bash "$SCRIPT" "$FIXTURE19" > /dev/null 2>&1
+    if [[ -f "$FIXTURE19/agents/foo.agent.md" ]] && [[ ! -L "$FIXTURE19/agents/foo.agent.md" ]]; then
+      pass "re-sync restores it to a regular file"
+    else
+      fail "re-sync did not restore the symlinked mirror entry to a regular file"
+    fi
   fi
 fi
 
@@ -639,6 +687,286 @@ else
   fi
 fi
 
+# --- 23. A credential in .mcp.json can never reach the published manifest ---
+# apm's own builder runs _sanitize_mcp_servers() (apm_cli/core/plugin_manifest.py)
+# before writing .claude-plugin/plugin.json — it drops env/environment/headers/
+# authorization and any key matching token/secret/password/credential/apikey/key at
+# any depth, because "copying them verbatim into a committed plugin.json would
+# exfiltrate them into the distributed artefact". The old jq --slurpfile
+# re-injection reached .github/plugin/plugin.json by a route that never touched the
+# sanitizer, so the same fixture produced a stripped Claude manifest and a Copilot
+# manifest carrying the live token. A path reference cannot carry a secret at all.
+echo ""
+echo "--- a token in .mcp.json never reaches .github/plugin/plugin.json ---"
+# Assembled at runtime, never written as a literal: a credential-shaped constant
+# in a tracked file is exactly what the gitleaks pre-commit hook exists to reject,
+# and allowlisting this file to keep one would blunt the scanner across every
+# future edit to it. The concatenation is what the leak test needs anyway — the
+# assertion is that this value does not survive into the manifest, and its shape
+# only has to be distinctive enough to grep for.
+SECRET="ghp""_TESTONLYnotarealcredential000000000000"
+FIXTURE23="$(make_fixture_with_mcp "{\"mcpServers\":{\"demo\":{\"command\":\"demo-server\",\"type\":\"stdio\",\"env\":{\"OBSIDIAN_API_TOKEN\":\"$SECRET\"}}}}")"; track "$FIXTURE23"
+bash "$SCRIPT" "$FIXTURE23" > /dev/null 2>&1
+if [[ ! -f "$FIXTURE23/.github/plugin/plugin.json" ]]; then
+  fail "sync produced no .github/plugin/plugin.json — cannot test the credential-leak case"
+else
+  if grep -q "$SECRET" "$FIXTURE23/.github/plugin/plugin.json"; then
+    fail "the .mcp.json token was written into .github/plugin/plugin.json — a tracked, marketplace-distributed file"
+  else
+    pass "no .mcp.json credential appears in the generated Copilot manifest"
+  fi
+  # The Claude-side manifest is apm's own output and is sanitized upstream; assert
+  # it too, so this case fails loudly if a future change starts routing the Claude
+  # manifest through the same re-injection.
+  if [[ -f "$FIXTURE23/.claude-plugin/plugin.json" ]] \
+    && grep -q "$SECRET" "$FIXTURE23/.claude-plugin/plugin.json"; then
+    fail "the .mcp.json token was written into .claude-plugin/plugin.json"
+  else
+    pass "no .mcp.json credential appears in the generated Claude manifest"
+  fi
+  if bash "$SCRIPT" --check "$FIXTURE23" > /dev/null 2>&1; then
+    pass "--check is clean on a freshly synced fixture whose .mcp.json carries an env block"
+  else
+    fail "--check reports drift on a freshly synced fixture carrying an .mcp.json env block"
+  fi
+fi
+
+# --- 24. .mcp.json drift is detected in both directions ---
+# The re-injection is the only writer of the manifest's mcpServers field, and
+# nothing covered it: --check could have silently stopped noticing either an
+# .mcp.json that gained servers or one that lost them.
+echo ""
+echo "--- adding servers to .mcp.json after a sync is drift ---"
+FIXTURE24="$(make_fixture_with_mcp '{"mcpServers":{}}')"; track "$FIXTURE24"
+bash "$SCRIPT" "$FIXTURE24" > /dev/null 2>&1
+if jq -e 'has("mcpServers")' "$FIXTURE24/.github/plugin/plugin.json" > /dev/null 2>&1; then
+  fail "an empty .mcp.json produced an mcpServers key — cannot test the gained-servers case"
+else
+  printf '%s' '{"mcpServers":{"demo":{"command":"demo-server","type":"stdio"}}}' > "$FIXTURE24/.mcp.json"
+  CHECK24="$(bash "$SCRIPT" --check "$FIXTURE24" 2>&1 || true)"
+  case "$CHECK24" in
+    *"DRIFT $FIXTURE24/.github/plugin/plugin.json"*)
+      pass "an .mcp.json that gained its first server is reported as drift" ;;
+    *)
+      fail "no drift reported for .github/plugin/plugin.json after .mcp.json gained a server" ;;
+  esac
+  bash "$SCRIPT" "$FIXTURE24" > /dev/null 2>&1
+  if bash "$SCRIPT" --check "$FIXTURE24" > /dev/null 2>&1; then
+    pass "re-sync clears the gained-server drift"
+  else
+    fail "re-sync did not clear the gained-server drift"
+  fi
+fi
+
+echo ""
+echo "--- emptying .mcp.json after a sync is drift ---"
+FIXTURE24B="$(make_fixture_with_mcp '{"mcpServers":{"demo":{"command":"demo-server","type":"stdio"}}}')"; track "$FIXTURE24B"
+bash "$SCRIPT" "$FIXTURE24B" > /dev/null 2>&1
+if ! jq -e '.mcpServers == ".mcp.json"' "$FIXTURE24B/.github/plugin/plugin.json" > /dev/null 2>&1; then
+  fail "initial sync did not re-inject mcpServers — cannot test the lost-servers case"
+else
+  printf '%s' '{"mcpServers":{}}' > "$FIXTURE24B/.mcp.json"
+  CHECK24B="$(bash "$SCRIPT" --check "$FIXTURE24B" 2>&1 || true)"
+  case "$CHECK24B" in
+    *"DRIFT $FIXTURE24B/.github/plugin/plugin.json"*)
+      pass "an .mcp.json emptied of its servers is reported as drift" ;;
+    *)
+      fail "no drift reported for .github/plugin/plugin.json after .mcp.json lost its servers" ;;
+  esac
+  bash "$SCRIPT" "$FIXTURE24B" > /dev/null 2>&1
+  if jq -e 'has("mcpServers") | not' "$FIXTURE24B/.github/plugin/plugin.json" > /dev/null 2>&1 \
+    && bash "$SCRIPT" --check "$FIXTURE24B" > /dev/null 2>&1; then
+    pass "re-sync drops the mcpServers key and clears the drift"
+  else
+    fail "re-sync did not drop mcpServers / did not clear the lost-server drift"
+  fi
+fi
+
+# --- 25. --check sees a mode change on the generated Copilot manifest ---
+# sync_plugin_manifest diffs that file's CONTENT only, and check_path_modes did not
+# cover .github/plugin/ at all — so the mode reinject_mcp_servers writes was outside
+# --check's manifest entirely, and check and sync could disagree about it forever.
+echo ""
+echo "--- --check detects a mode change on .github/plugin/plugin.json ---"
+FIXTURE25="$(make_fixture_with_mcp '{"mcpServers":{"demo":{"command":"demo-server","type":"stdio"}}}')"; track "$FIXTURE25"
+bash "$SCRIPT" "$FIXTURE25" > /dev/null 2>&1
+if ! bash "$SCRIPT" --check "$FIXTURE25" > /dev/null 2>&1; then
+  fail "check reported drift right after the initial sync — cannot test the manifest-mode case"
+else
+  chmod 600 "$FIXTURE25/.github/plugin/plugin.json"
+  CHECK25="$(bash "$SCRIPT" --check "$FIXTURE25" 2>&1 || true)"
+  case "$CHECK25" in
+    *"mirrored paths/types/modes differ"*)
+      pass "a mode change on .github/plugin/plugin.json is reported as drift" ;;
+    *)
+      fail "no mode drift reported after chmod 600 on .github/plugin/plugin.json" ;;
+  esac
+  bash "$SCRIPT" "$FIXTURE25" > /dev/null 2>&1
+  MODE25="$(stat -c '%a' "$FIXTURE25/.github/plugin/plugin.json" 2>/dev/null \
+    || stat -f '%Lp' "$FIXTURE25/.github/plugin/plugin.json" 2>/dev/null)"
+  if [[ "$MODE25" == "644" ]] && bash "$SCRIPT" --check "$FIXTURE25" > /dev/null 2>&1; then
+    pass "re-sync restores mode 644 and clears the drift"
+  else
+    fail "re-sync left .github/plugin/plugin.json at mode $MODE25 / did not clear the drift"
+  fi
+fi
+
+# --- 26. --check compares full permission bits, not just the exec bit ---
+# The manifest used to record a bare exec/file kind, so `chmod 444` on a mirrored
+# SKILL.md left --check at exit 0 while a real sync restored 644 — the same
+# check/sync disagreement case 18 pins for the exec bit, one bit over.
+echo ""
+echo "--- --check detects a non-exec permission change on a mirrored file ---"
+FIXTURE26="$(make_fixture)"; track "$FIXTURE26"
+bash "$SCRIPT" "$FIXTURE26" > /dev/null 2>&1
+if [[ ! -f "$FIXTURE26/skills/hello/SKILL.md" ]]; then
+  fail "sync did not mirror skills/hello/SKILL.md — cannot test the permission-bits case"
+else
+  chmod 444 "$FIXTURE26/skills/hello/SKILL.md"
+  CHECK26="$(bash "$SCRIPT" --check "$FIXTURE26" 2>&1 || true)"
+  case "$CHECK26" in
+    *"mirrored paths/types/modes differ"*)
+      pass "chmod 444 on a mirrored file is reported as drift" ;;
+    *)
+      fail "no drift reported after chmod 444 on a mirrored file — only the exec bit is being compared" ;;
+  esac
+  bash "$SCRIPT" "$FIXTURE26" > /dev/null 2>&1
+  if bash "$SCRIPT" --check "$FIXTURE26" > /dev/null 2>&1; then
+    pass "re-sync restores the permission bits and clears the drift"
+  else
+    fail "re-sync did not clear the permission-bits drift"
+  fi
+fi
+
+# --- 27. A plugin-dir argument whose basename is . or .. is rejected ---
+# Every scratch path is "$SCRATCH_ROOT/$(basename "$plugin_dir")", so `..` resolves
+# to the scratch root's PARENT: `apm pack -o` then writes outside the tree the EXIT
+# trap cleans, and sync_one's `find "$scratch" -mindepth 1 -maxdepth 1 -type d |
+# head -1` adopts an arbitrary unrelated directory as the "bundle" — whose contents
+# a real sync cp -a's into the plugin root after an rm -rf. The duplicate-basename
+# guard cannot catch it: a single `..` collides with nothing.
+echo ""
+echo "--- a plugin dir whose basename is . or .. is rejected ---"
+for TRAVERSAL in . ..; do
+  RC27=0
+  OUT27="$(bash "$SCRIPT" "$TRAVERSAL" 2>&1)" || RC27=$?
+  case "$RC27:$OUT27" in
+    0:*)
+      fail "'$TRAVERSAL' was accepted as a plugin dir — expected a rejection" ;;
+    *"scratch paths built from it would escape the scratch root"*)
+      pass "'$TRAVERSAL' is rejected with a scratch-path-escape error" ;;
+    *)
+      fail "'$TRAVERSAL' was not rejected with the expected message (rc=$RC27): $OUT27" ;;
+  esac
+done
+
+# --- 27b. sync_dir and sync_hooks_json refuse an empty target_dir ---
+# `set -u` aborts on an UNSET variable but not an empty one, so an empty
+# $target_dir turns both functions' `rm -rf` calls into `rm -rf /agents`,
+# `/skills`, `/commands`, `/instructions`, `/extensions`, `/hooks`. Unreachable
+# from today's two call sites (both pass a validated plugin_dir or a scratch
+# path), which is exactly why it needs a direct test: no end-to-end invocation
+# can reach it, and the next caller added is the one that finds out.
+#
+# The functions are extracted and run with rm/mkdir/cp/find shadowed by loggers,
+# so the UNGUARDED form is observed rather than executed — running it for real,
+# as root, is the outcome the guard exists to prevent.
+echo ""
+echo "--- sync_dir/sync_hooks_json abort on an empty target_dir instead of rm -rf'ing / ---"
+for GUARDED_FN in sync_dir sync_hooks_json; do
+  FNSRC="$(awk -v fn="^${GUARDED_FN}\\\\(\\\\) \\\\{$" '$0 ~ fn, /^\}$/' "$SCRIPT")"
+  if [[ -z "$FNSRC" ]] || [[ "$FNSRC" != *"rm -rf"* ]]; then
+    fail "could not extract $GUARDED_FN() from $SCRIPT — this case is testing nothing"
+    continue
+  fi
+  GUARD_BUNDLE="$(mktemp -d)"; track "$GUARD_BUNDLE"
+  mkdir -p "$GUARD_BUNDLE/agents"
+  printf '{}\n' > "$GUARD_BUNDLE/hooks.json"
+  GUARD_LOG="$(mktemp)"; track "$GUARD_LOG"
+  # HOOKS_DIR_REL/HOOKS_REL/LEGACY_HOOKS_REL are script globals sync_hooks_json
+  # reads; supply them so the extracted copy behaves like the real one.
+  RC27B=0
+  bash -c '
+    set -euo pipefail
+    LOG="$2"
+    HOOKS_DIR_REL="hooks"; HOOKS_REL="hooks/hooks.json"; LEGACY_HOOKS_REL="hooks.json"
+    rm()    { printf "rm %s\n"    "$*" >> "$LOG"; }
+    mkdir() { printf "mkdir %s\n" "$*" >> "$LOG"; }
+    cp()    { printf "cp %s\n"    "$*" >> "$LOG"; }
+    find()  { printf "find %s\n"  "$*" >> "$LOG"; }
+    '"$FNSRC"'
+    '"$GUARDED_FN"' "" "$1" agents
+  ' _ "$GUARD_BUNDLE" "$GUARD_LOG" > /dev/null 2>&1 || RC27B=$?
+  DANGEROUS="$(grep -E '(^| )/(agents|skills|commands|instructions|extensions|hooks)([[:space:]]|$)' "$GUARD_LOG" 2>/dev/null || true)"
+  if [[ "$RC27B" -ne 0 ]] && [[ -z "$DANGEROUS" ]]; then
+    pass "$GUARDED_FN aborts on an empty target_dir before touching any path"
+  else
+    fail "$GUARDED_FN with an empty target_dir exited $RC27B and would have run:${DANGEROUS:-<nothing logged>}"
+  fi
+done
+
+# --- 28. --all refuses to report success over an unusable or empty marketplace ---
+# check-plugin-content-sync is the one pre-push gate whose work list comes from a
+# GENERATED file, so "the marketplace yields nothing" must never mean "verified,
+# no drift" — regenerating marketplace.json badly would otherwise silence the hook
+# that guards it. Every case below reached exit 0 before: the process substitution
+# feeding `while read` is its own subshell, so a jq abort in there yields zero lines
+# and reads exactly like "declares no local plugins".
+echo ""
+echo "--- --check --all fails on a marketplace that yields no plugins ---"
+make_repo_fixture() {
+  local marketplace_json="$1" dir
+  dir="$(mktemp -d)"
+  dir="$(cd "$dir" && pwd -P)"
+  if ! env -u GIT_DIR -u GIT_WORK_TREE git -C "$dir" init -q >/dev/null 2>&1; then
+    echo "make_repo_fixture: 'git init' failed in $dir" >&2
+    exit 1
+  fi
+  mkdir -p "$dir/.claude-plugin"
+  printf '%s' "$marketplace_json" > "$dir/.claude-plugin/marketplace.json"
+  echo "$dir"
+}
+# `env -u GIT_DIR -u GIT_WORK_TREE` for the same reason
+# tests/test-sync-marketplace-mirror.sh does it: run-tests.sh runs as a pre-push
+# hook, and git hooks export both variables, which would re-target the script's
+# `git rev-parse --show-toplevel` at the LIVE repo from any cwd.
+run_all() {
+  local dir="$1"
+  shift
+  (cd "$dir" && env -u GIT_DIR -u GIT_WORK_TREE bash "$SCRIPT" "$@")
+}
+# Message-asserted, not just exit-code-asserted: --all has several independent
+# routes to exit 1 (missing marketplace, apm pack failure, genuine drift), and an
+# exit-code-only assertion would pass on any of them.
+check_all_fails_with() {
+  local desc="$1" marketplace_json="$2" expected="$3" dir out rc=0
+  dir="$(make_repo_fixture "$marketplace_json")"; track "$dir"
+  out="$(run_all "$dir" --check --all 2>&1)" || rc=$?
+  if [[ "$rc" -eq 0 ]]; then
+    fail "$desc: --check --all exited 0 having checked nothing"
+  else
+    case "$out" in
+      *"$expected"*) pass "$desc: rejected with the expected message" ;;
+      *) fail "$desc: exited non-zero but not for the expected reason: $out" ;;
+    esac
+  fi
+}
+check_all_fails_with "an empty plugins array" \
+  '{"plugins":[]}' \
+  "declares no local (string-source) plugin entries"
+check_all_fails_with "a marketplace with no plugins key at all" \
+  '{"name":"x"}' \
+  "declares no local (string-source) plugin entries"
+check_all_fails_with "unparseable JSON" \
+  '{ not json' \
+  "is not valid JSON"
+check_all_fails_with "a plugins field that is not an array" \
+  '{"plugins":{"a":1}}' \
+  "expected an array of plugin entries"
+check_all_fails_with "an entry with no source field" \
+  '{"plugins":[{"name":"orphan"}]}' \
+  "entries with no \`source\` field"
+
 echo ""
 echo "Results: $PASS passed, $FAIL failed"
 [[ $FAIL -eq 0 ]]