fix(scripts): bring the generated hooks/ directory under the mirror's ownership

`checked_paths` covered hooks/hooks.json but not the hooks/ directory
holding it, so a stray file dropped inside, or an empty hooks/ left
behind once .apm/hooks/ stopped producing anything, was invisible to
--check. Check and sync agreed in both cases, so the invariant held --
but a stray in a directory the mirror owns should be drift, exactly as
it is inside skills/ or agents/. A stray at the PLUGIN root stays out
of scope by design: README.md, docs/, bin/, .mcp.json are hand-authored.

hooks/ is now wiped and rebuilt like every MIRROR_DIRS destination, and
the directory is listed in checked_paths so the recursive manifest sees
one-sided entries.

Issue #97 item 4 reports `prompts` as documented-but-unmirrored. That is
refuted: MIRROR_DIRS lists DESTINATION directories, and apm folds
.apm/prompts/ into commands/ (renaming *.prompt.md to *.md), verified
empirically. A plugin adding .apm/prompts/ is mirrored today; adding a
`prompts` entry would name an output directory apm never emits. Pinned
with a characterization test that fires if that mapping ever changes,
plus a comment so it is not refiled.

Guards the new wipe with ${target_dir:?}: `set -u` aborts on an unset
variable but not an empty one, which would make it `rm -rf /hooks`.

Refs #97

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X7GvKuJfy2WrdBmUttV4DT

tests/test-sync-plugin-content.sh

@@ -17,7 +17,9 @@ fi
 # Minimal fixture exercising every mirrored category -- all five of
 # scripts/sync-plugin-content.sh's MIRROR_DIRS (agents, skills, commands,
 # instructions, extensions) plus the merged hooks file -- without needing network
-# access (no apm.yml dependencies). Two deliberately-shaped skill subdirectories:
+# access (no apm.yml dependencies). It also carries a .apm/prompts/ entry, which has
+# no MIRROR_DIRS destination of its own: apm folds prompts into commands/. Two
+# deliberately-shaped skill subdirectories:
 #
 #   skills/hello/tests/                    -- a dev-time fixture that must NOT be mirrored
 #   skills/hello/assets/templates/tests/   -- a template asset that MUST be mirrored
@@ -34,7 +36,7 @@ make_fixture() {
   mkdir -p "$dir/.apm/skills/hello/tests" "$dir/.apm/skills/hello/scripts" \
     "$dir/.apm/skills/hello/assets/templates/tests" "$dir/.apm/agents" \
     "$dir/.apm/hooks" "$dir/.apm/commands" "$dir/.apm/instructions" \
-    "$dir/.apm/extensions"
+    "$dir/.apm/extensions" "$dir/.apm/prompts"
   cat > "$dir/apm.yml" <<'YAML'
 name: fixture
 version: 0.0.1
@@ -81,6 +83,12 @@ EOF
 description: mycmd
 ---
 Do a thing.
+EOF
+  cat > "$dir/.apm/prompts/greet.prompt.md" <<'EOF'
+---
+description: greet
+---
+Greet the user.
 EOF
   cat > "$dir/.apm/instructions/style.instructions.md" <<'EOF'
 ---
@@ -539,6 +547,98 @@ else
   fi
 fi
 
+# --- 20. .apm/prompts/ is mirrored, via commands/ rather than a prompts/ of its own ---
+# The script header lists prompts among the .apm/ directories it mirrors while
+# MIRROR_DIRS has no `prompts` entry, which reads as a hole and has already been filed
+# as one. It is not: MIRROR_DIRS names DESTINATION directories, and apm's exporter
+# folds .apm/prompts/ into commands/ (renaming *.prompt.md to *.md) alongside
+# .apm/commands/. This pins that mapping, so an apm upgrade that gave prompts a
+# destination of its own — the one change that would genuinely need a MIRROR_DIRS
+# entry — fails here instead of silently dropping the content.
+echo ""
+echo "--- .apm/prompts/ content arrives in commands/, not in a prompts/ directory ---"
+FIXTURE20="$(make_fixture)"; track "$FIXTURE20"
+bash "$SCRIPT" "$FIXTURE20" > /dev/null 2>&1
+if [[ -f "$FIXTURE20/commands/greet.md" ]]; then
+  pass ".apm/prompts/greet.prompt.md is mirrored to commands/greet.md"
+else
+  fail ".apm/prompts/ content never reached commands/ — apm's prompts mapping changed"
+fi
+if [[ ! -e "$FIXTURE20/prompts" ]]; then
+  pass "no prompts/ directory is produced at the plugin root"
+else
+  fail "a prompts/ directory appeared at the plugin root — it now needs a MIRROR_DIRS entry"
+fi
+if bash "$SCRIPT" --check "$FIXTURE20" > /dev/null 2>&1; then
+  pass "--check is clean with .apm/prompts/ content present"
+else
+  fail "--check reports drift on a freshly synced fixture carrying .apm/prompts/"
+fi
+
+# --- 21. A stray file inside the generated hooks/ directory is drift ---
+# hooks/ is mirror-owned output, so it is scoped like a MIRROR_DIRS destination and
+# not like the plugin root (where README.md, docs/, bin/ and .mcp.json are all
+# hand-authored and deliberately none of this script's business). Before hooks/ came
+# under that ownership, --check exited 0 on a stray inside it and a real sync left the
+# stray untouched — agreeing with each other, but agreeing on the wrong answer.
+echo ""
+echo "--- a stray file inside the generated hooks/ directory is reported and removed ---"
+FIXTURE21="$(make_fixture)"; track "$FIXTURE21"
+bash "$SCRIPT" "$FIXTURE21" > /dev/null 2>&1
+if [[ ! -f "$FIXTURE21/hooks/hooks.json" ]]; then
+  fail "initial sync did not create hooks/hooks.json -- can't test the stray case"
+else
+  printf '{"stray": true}\n' > "$FIXTURE21/hooks/extra.json"
+  if bash "$SCRIPT" --check "$FIXTURE21" > /dev/null 2>&1; then
+    fail "no drift reported for a stray file inside the generated hooks/ directory"
+  else
+    pass "a stray file inside hooks/ is reported as drift"
+    bash "$SCRIPT" "$FIXTURE21" > /dev/null 2>&1
+    if [[ ! -e "$FIXTURE21/hooks/extra.json" ]] && [[ -f "$FIXTURE21/hooks/hooks.json" ]]; then
+      pass "re-sync removes the stray and keeps hooks/hooks.json"
+    else
+      fail "re-sync did not clean the stray out of hooks/"
+    fi
+    if bash "$SCRIPT" --check "$FIXTURE21" > /dev/null 2>&1; then
+      pass "re-sync clears the stray-hooks-file drift"
+    else
+      fail "re-sync did not clear the stray-hooks-file drift"
+    fi
+  fi
+fi
+
+# --- 22. An empty leftover hooks/ directory is drift, not an acceptable resting state ---
+# When .apm/hooks/ produces no hooks.json, the correct mirror state is no hooks/
+# directory at all — not an empty one. Empty leftovers are exactly what earlier
+# revisions of this script left behind in this repo's own plugin roots.
+echo ""
+echo "--- an empty leftover hooks/ directory is reported and removed ---"
+FIXTURE22="$(make_fixture)"; track "$FIXTURE22"
+rm -rf "$FIXTURE22/.apm/hooks"
+bash "$SCRIPT" "$FIXTURE22" > /dev/null 2>&1
+if [[ -e "$FIXTURE22/hooks" ]]; then
+  fail "sync created hooks/ for a plugin whose .apm/hooks/ produces no hooks.json"
+else
+  pass "no hooks/ directory when .apm/hooks/ produces nothing"
+fi
+mkdir -p "$FIXTURE22/hooks"
+if bash "$SCRIPT" --check "$FIXTURE22" > /dev/null 2>&1; then
+  fail "no drift reported for an empty leftover hooks/ directory"
+else
+  pass "an empty leftover hooks/ directory is reported as drift"
+  bash "$SCRIPT" "$FIXTURE22" > /dev/null 2>&1
+  if [[ ! -e "$FIXTURE22/hooks" ]]; then
+    pass "re-sync removes the empty leftover hooks/ directory"
+  else
+    fail "re-sync left the empty hooks/ directory in place"
+  fi
+  if bash "$SCRIPT" --check "$FIXTURE22" > /dev/null 2>&1; then
+    pass "re-sync clears the empty-hooks-directory drift"
+  else
+    fail "re-sync did not clear the empty-hooks-directory drift"
+  fi
+fi
+
 echo ""
 echo "Results: $PASS passed, $FAIL failed"
 [[ $FAIL -eq 0 ]]