diff --git a/.github/workflows/gate.yml b/.github/workflows/gate.yml
index 2b2b368..46e8def 100644
--- a/.github/workflows/gate.yml
+++ b/.github/workflows/gate.yml
@@ -32,6 +32,8 @@ jobs:
             bash -n "$f"
             echo "::endgroup::"
           done
+      - name: Sync owned-path regressions
+        run: bash omp-port/test-sync-owned-paths.sh
       - name: Port gate
         run: bash omp-port/check-port.sh
       - name: Install script test dependencies
diff --git a/PORTING.md b/PORTING.md
index 74ef846..ea7f235 100644
--- a/PORTING.md
+++ b/PORTING.md
@@ -40,6 +40,10 @@ upstream text at the pinned sha minus the paths in `omp-port/excluded.txt`, with
 check, which rebuilds the pin and diffs it against the tree, and the next build deletes it. Put the
 change in `rules.sed`, in a patch, or in an owned path instead.
 
+Before a sync replaces the skill and agent trees, it rejects uncommitted changes within them unless
+the changed path is owned or is below an owned directory. A similarly named sibling is not owned.
+Run `bash omp-port/test-sync-owned-paths.sh` to check this behavior in isolated repositories.
+
 The `upstream-sync` workflow does this daily. It runs `bash omp-port/check-port.sh` on `main` first,
 so a red trunk stops the run rather than being merged over, then builds at the newest upstream
 commit that touched `pstack/`, opens a PR carrying the sync and gate output in its body, and squash
diff --git a/omp-port/sync-upstream.sh b/omp-port/sync-upstream.sh
index 63b2839..d2065e1 100755
--- a/omp-port/sync-upstream.sh
+++ b/omp-port/sync-upstream.sh
@@ -105,7 +105,7 @@ do_build() {
 }
 
 cmd_sync() {
-	local target="${1:-}" pin touched dirty p
+	local target="${1:-}" pin touched p rel
 	pin=$(read_pin)
 	[ -n "$target" ] || target=$(upstream_head)
 	[[ $target =~ ^[0-9a-f]{40}$ ]] || die "target must be a full 40-hex sha, got '$target'"
@@ -118,14 +118,17 @@ cmd_sync() {
 	fi
 	# Only the built tree is destroyed by a sync, and owned paths are carried across it, so an
 	# uncommitted owned file or an edit anywhere else is not a reason to refuse.
-	dirty=$(git status --porcelain -- plugins/pstack/skills plugins/pstack/agents | sed 's/^...//')
-	while IFS= read -r p; do
-		dirty=$(printf '%s\n' "$dirty" | grep -v "^plugins/pstack/$p" || true)
-	done < <(owned_paths)
-	if [ -n "$(printf '%s' "$dirty" | tr -d '[:space:]')" ]; then
-		printf '%s\n' "$dirty" >&2
-		die "uncommitted changes the build would destroy, commit or stash them first"
-	fi
+	git status --porcelain -z --no-renames --untracked-files=all -- plugins/pstack/skills plugins/pstack/agents |
+		while IFS= read -r -d '' p; do
+			p=${p:3}
+			while IFS= read -r rel; do
+				if [[ "$p" == "plugins/pstack/$rel" || "$p" == "plugins/pstack/$rel/"* ]]; then
+					continue 2
+				fi
+			done < <(owned_paths)
+			printf '%q\n' "$p" >&2
+			die "uncommitted changes the build would destroy, commit or stash them first"
+		done
 	do_build "$target" "$pin" yes
 }
 
diff --git a/omp-port/test-sync-owned-paths.sh b/omp-port/test-sync-owned-paths.sh
new file mode 100755
index 0000000..71b218a
--- /dev/null
+++ b/omp-port/test-sync-owned-paths.sh
@@ -0,0 +1,176 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+PORT_DIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd -P)
+WORK=$(mktemp -d)
+trap 'rm -rf "$WORK"' EXIT
+fail=0
+
+init_repo() {
+	git -C "$1" init -q
+	git -C "$1" config user.name 'Sync fixture'
+	git -C "$1" config user.email sync-fixture@example.invalid
+	git -C "$1" config commit.gpgsign false
+	git -C "$1" config core.hooksPath /dev/null
+	git -C "$1" config core.quotePath true
+	git -C "$1" config status.renames true
+}
+
+mkdir -p "$WORK/canon/pstack/"{.cursor-plugin,skills/poteto-mode/playbooks,skills/upstream,agents}
+printf '{"version":"1.0.0"}\n' >"$WORK/canon/pstack/.cursor-plugin/plugin.json"
+printf 'playbook\n' >"$WORK/canon/pstack/skills/poteto-mode/playbooks/example.md"
+printf 'rename source\n' >"$WORK/canon/pstack/skills/upstream/rename.txt"
+printf 'agent\n' >"$WORK/canon/pstack/agents/example.md"
+init_repo "$WORK/canon"
+git -C "$WORK/canon" add .
+git -C "$WORK/canon" commit -qm 'Fixture pin'
+PIN=$(git -C "$WORK/canon" rev-parse HEAD)
+printf 'new upstream content\n' >"$WORK/canon/pstack/skills/upstream/target.txt"
+git -C "$WORK/canon" add .
+git -C "$WORK/canon" commit -qm 'Fixture target'
+TARGET=$(git -C "$WORK/canon" rev-parse HEAD)
+export TARGET
+
+gh() { printf '%s\t%s\t2026-01-01\tfixture target\n' "$TARGET" "${TARGET:0:7}"; }
+export -f gh
+git() {
+	if [ "${SYNC_FIXTURE_STATUS_FAIL:-}" = 1 ] && [ "${1:-}" = status ]; then
+		printf 'fixture status failure\n' >&2
+		return 73
+	fi
+	command git "$@"
+}
+export -f git
+
+mkdir -p "$WORK/template/"{omp-port/patches,plugins/pstack,.omp-plugin}
+cp "$PORT_DIR/"{sync-upstream.sh,lib.sh} "$WORK/template/omp-port/"
+git -C "$WORK/canon" archive "$PIN" pstack/skills pstack/agents |
+	tar -x --strip-components=1 -C "$WORK/template/plugins/pstack"
+for p in skills/pstack-omp skills/omp-mechanics 'skills/local[.]owner'; do
+	mkdir -p "$WORK/template/plugins/pstack/$p"
+	printf 'owned content\n' >"$WORK/template/plugins/pstack/$p/SKILL.md"
+done
+printf 'owned file\n' >"$WORK/template/plugins/pstack/skills/local-file"
+printf '%s\t-\n' skills/pstack-omp skills/omp-mechanics 'skills/local[.]owner' skills/local-file \
+	>"$WORK/template/omp-port/owned.txt"
+printf '%s\n' "$PIN" >"$WORK/template/omp-port/UPSTREAM"
+cp "$PORT_DIR/rules.sed" "$WORK/template/omp-port/rules.sed"
+: >"$WORK/template/omp-port/excluded.txt"
+printf '{"version":"1.0.0"}\n' >"$WORK/template/plugins/pstack/package.json"
+printf '{"metadata":{"version":"1.0.0"},"plugins":[{"name":"pstack","version":"1.0.0","description":"fixture"}]}\n' \
+	>"$WORK/template/.omp-plugin/marketplace.json"
+init_repo "$WORK/template"
+git -C "$WORK/template" add .
+git -C "$WORK/template" commit -qm 'Fixture port'
+
+run_case() {
+	local name="$1" expected="$2" mutation="$3" dir="$WORK/$1" status=0 ok=1 p reviewed
+	local status_fail=0
+	cp -a "$WORK/template" "$dir"
+	FIXTURE="$dir"
+	"$mutation"
+	cp -a "$dir/plugins/pstack" "$dir/before"
+	cp "$dir/omp-port/UPSTREAM" "$dir/pin.before"
+	CANON="$WORK/canon" RULES="$dir/omp-port/rules.sed" OWNED="$dir/omp-port/owned.txt" \
+		EXCLUDED="$dir/omp-port/excluded.txt" PATCH_DIR="$dir/omp-port/patches" SYNC_FIXTURE_STATUS_FAIL="$status_fail" \
+		bash "$dir/omp-port/sync-upstream.sh" "$TARGET" >"$dir/out" 2>&1 || status=$?
+	if [ "$expected" != allow ]; then
+		if [ "$expected" = reject ]; then
+			[ "$status" -ne 0 ] || ok=0
+			grep -qF 'uncommitted changes the build would destroy' "$dir/out" || ok=0
+		else
+			[ "$status" -eq 73 ] || ok=0
+			grep -qF 'fixture status failure' "$dir/out" || ok=0
+		fi
+		cmp -s "$dir/pin.before" "$dir/omp-port/UPSTREAM" || ok=0
+		diff -r "$dir/before" "$dir/plugins/pstack" >>"$dir/out" 2>&1 || ok=0
+	else
+		[ "$status" -eq 0 ] || ok=0
+		[ "$(cat "$dir/omp-port/UPSTREAM")" = "$TARGET" ] || ok=0
+		cmp -s "$WORK/canon/pstack/skills/upstream/target.txt" \
+			"$dir/plugins/pstack/skills/upstream/target.txt" || ok=0
+		while IFS=$'\t' read -r p reviewed; do
+			diff -r "$dir/before/$p" "$dir/plugins/pstack/$p" >>"$dir/out" 2>&1 || ok=0
+		done <"$dir/omp-port/owned.txt"
+	fi
+	if [ "$ok" -eq 1 ]; then
+		printf 'sync owned paths: %s PASS\n' "$name"
+	else
+		printf 'sync owned paths: %s FAIL, expected %s, exit %s\n' "$name" "$expected" "$status"
+		cat "$dir/out"
+		fail=1
+	fi
+}
+
+nothing() { :; }
+
+status_failure() { status_fail=1; }
+
+untracked_prefix_sibling() {
+	mkdir -p "$FIXTURE/plugins/pstack/skills/pstack-omp-audit"
+	printf 'irreplaceable local edit\000\377\n' >"$FIXTURE/plugins/pstack/skills/pstack-omp-audit/local.txt"
+}
+
+owned_edit() {
+	printf 'local owned edit\n' >>"$FIXTURE/plugins/pstack/skills/pstack-omp/SKILL.md"
+}
+
+owned_quoted_name() {
+	printf 'local bytes\000\377\n' >"$FIXTURE/plugins/pstack/skills/pstack-omp/"$'quote"\tline\n\377notes.txt'
+}
+
+unowned_quoted_name() {
+	mkdir -p "$FIXTURE/plugins/pstack/skills/"$'pstack-omp-audit"\tline\n\377'
+	printf 'local bytes\000\377\n' >"$FIXTURE/plugins/pstack/skills/"$'pstack-omp-audit"\tline\n\377/local.txt'
+}
+
+owned_file_edit() {
+	printf 'local file edit\n' >>"$FIXTURE/plugins/pstack/skills/local-file"
+}
+
+owned_file_suffix() {
+	printf 'not owned\n' >"$FIXTURE/plugins/pstack/skills/local-file.bak"
+}
+
+literal_owned_edit() {
+	printf 'literal owned edit\n' >>"$FIXTURE/plugins/pstack/skills/local[.]owner/SKILL.md"
+}
+
+regex_lookalike() {
+	mkdir -p "$FIXTURE/plugins/pstack/skills/local.owner"
+	printf 'not owned\n' >"$FIXTURE/plugins/pstack/skills/local.owner/local.txt"
+}
+
+rename_out_of_owned() {
+	git -C "$FIXTURE" mv plugins/pstack/skills/pstack-omp/SKILL.md plugins/pstack/skills/pstack-omp-audit.md
+}
+
+rename_into_owned() {
+	git -C "$FIXTURE" mv plugins/pstack/skills/upstream/rename.txt plugins/pstack/skills/pstack-omp/renamed.txt
+}
+
+rename_within_owned() {
+	git -C "$FIXTURE" mv plugins/pstack/skills/pstack-omp/SKILL.md plugins/pstack/skills/pstack-omp/renamed.md
+}
+
+agent_edit() {
+	printf 'local agent edit\n' >>"$FIXTURE/plugins/pstack/agents/example.md"
+}
+
+run_case baseline allow nothing
+run_case untracked-prefix-sibling reject untracked_prefix_sibling
+run_case owned-edit allow owned_edit
+run_case owned-quoted-name allow owned_quoted_name
+run_case unowned-quoted-name reject unowned_quoted_name
+run_case owned-file-edit allow owned_file_edit
+run_case owned-file-suffix reject owned_file_suffix
+run_case literal-owned-edit allow literal_owned_edit
+run_case regex-lookalike reject regex_lookalike
+run_case rename-out-of-owned reject rename_out_of_owned
+run_case rename-into-owned reject rename_into_owned
+run_case rename-within-owned allow rename_within_owned
+run_case agent-edit reject agent_edit
+run_case status-error status-error status_failure
+
+[ "$fail" -eq 0 ] || exit 1
+printf 'sync owned paths: PASS\n'