fix(installer): detect same-metadata content updates

install-skills.sh

@@ -365,7 +365,7 @@ install_plugin() {
     else
       mkdir -p "$dst_dir"
       # rsync resolved source (handles nested skills/ structures)
-      rsync -a --delete "$src_dir/" "$dst_dir/"
+      rsync -a --checksum --delete "$src_dir/" "$dst_dir/"
       state_set "$install_name" "$version" "$effective_install_type" "$source_digest"
       ok "$install_name → skill (v$version)"
       INSTALL_ACTION=true

tests/install-skills.test.sh

@@ -42,6 +42,9 @@ description: Installer fixture version two.
 ---
 version two
 EOF
+# Reproduce rsync's quick-check edge case: changed content with identical size
+# and mtime must still replace the recorded, unmodified installation.
+touch -r "$TEST_HOME/.agents/skills/example/SKILL.md" "$FIXTURE_REPO/skills-dev/example-plugin/skills/SKILL.md"
 HOME="$TEST_HOME" "$FIXTURE_REPO/install-skills.sh" >/dev/null
 grep -q 'version two' "$TEST_HOME/.agents/skills/example/SKILL.md"
 grep -q '"version": "2.0.0"' "$TEST_HOME/.agents/.ai-proj-helper-installed-skills.json"