diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4a98b635..c5a3a56b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,15 @@
 # Changelog
 
+## 0.5.4.1 — 2026-03-17
+
+- **`/gstack-upgrade` now catches stale vendored copies automatically.** If your global gstack is up to date but the vendored copy in your project is behind, `/gstack-upgrade` detects the mismatch and syncs it. No more manually asking "did we vendor it?" — it just tells you and offers to update.
+- **Upgrade sync is safer.** If `./setup` fails while syncing a vendored copy, gstack restores the previous version from backup instead of leaving a broken install.
+
+### For contributors
+
+- Standalone usage section in `gstack-upgrade/SKILL.md.tmpl` now references Steps 2 and 4.5 (DRY) instead of duplicating detection/sync bash blocks. Added one new version-comparison bash block.
+- Update check fallback in standalone mode now matches the preamble pattern (global path → local path → `|| true`).
+
 ## 0.5.4 — 2026-03-17
 
 - **Engineering review is always the full review now.** `/plan-eng-review` no longer asks you to choose between "big change" and "small change" modes. Every plan gets the full interactive walkthrough (architecture, code quality, tests, performance). Scope reduction is only suggested when the complexity check actually triggers — not as a standing menu option.
diff --git a/VERSION b/VERSION
index 7d856835..01b7df36 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.5.4
+0.5.4.1
diff --git a/gstack-upgrade/SKILL.md b/gstack-upgrade/SKILL.md
index 9d635651..50b67dfc 100644
--- a/gstack-upgrade/SKILL.md
+++ b/gstack-upgrade/SKILL.md
@@ -156,6 +156,13 @@ rm -rf "$LOCAL_GSTACK.bak"
 ```
 Tell user: "Also updated vendored copy at `$LOCAL_GSTACK` — commit `.claude/skills/gstack/` when you're ready."
 
+If `./setup` fails, restore from backup and warn the user:
+```bash
+rm -rf "$LOCAL_GSTACK"
+mv "$LOCAL_GSTACK.bak" "$LOCAL_GSTACK"
+```
+Tell user: "Sync failed — restored previous version at `$LOCAL_GSTACK`. Run `/gstack-upgrade` manually to retry."
+
 ### Step 5: Write marker + clear cache
 
 ```bash
@@ -193,9 +200,26 @@ When invoked directly as `/gstack-upgrade` (not from a preamble):
 
 1. Force a fresh update check (bypass cache):
 ```bash
-~/.claude/skills/gstack/bin/gstack-update-check --force
+~/.claude/skills/gstack/bin/gstack-update-check --force 2>/dev/null || \
+.claude/skills/gstack/bin/gstack-update-check --force 2>/dev/null || true
 ```
 Use the output to determine if an upgrade is available.
 
 2. If `UPGRADE_AVAILABLE <old> <new>`: follow Steps 2-6 above.
-3. If no output (up to date): tell the user "You're already on the latest version (v{version})."
+
+3. If no output (primary is up to date): check for a stale local vendored copy.
+
+Run the Step 2 bash block above to detect the primary install type and directory (`INSTALL_TYPE` and `INSTALL_DIR`). Then run the Step 4.5 detection bash block above to check for a local vendored copy (`LOCAL_GSTACK`).
+
+**If `LOCAL_GSTACK` is empty** (no local vendored copy): tell the user "You're already on the latest version (v{version})."
+
+**If `LOCAL_GSTACK` is non-empty**, compare versions:
+```bash
+PRIMARY_VER=$(cat "$INSTALL_DIR/VERSION" 2>/dev/null || echo "unknown")
+LOCAL_VER=$(cat "$LOCAL_GSTACK/VERSION" 2>/dev/null || echo "unknown")
+echo "PRIMARY=$PRIMARY_VER LOCAL=$LOCAL_VER"
+```
+
+**If versions differ:** follow the Step 4.5 sync bash block above to update the local copy from the primary. Tell user: "Global v{PRIMARY_VER} is up to date. Updated local vendored copy from v{LOCAL_VER} → v{PRIMARY_VER}. Commit `.claude/skills/gstack/` when you're ready."
+
+**If versions match:** tell the user "You're on the latest version (v{PRIMARY_VER}). Global and local vendored copy are both up to date."
diff --git a/gstack-upgrade/SKILL.md.tmpl b/gstack-upgrade/SKILL.md.tmpl
index a441b8d6..0acf16c2 100644
--- a/gstack-upgrade/SKILL.md.tmpl
+++ b/gstack-upgrade/SKILL.md.tmpl
@@ -154,6 +154,13 @@ rm -rf "$LOCAL_GSTACK.bak"
 ```
 Tell user: "Also updated vendored copy at `$LOCAL_GSTACK` — commit `.claude/skills/gstack/` when you're ready."
 
+If `./setup` fails, restore from backup and warn the user:
+```bash
+rm -rf "$LOCAL_GSTACK"
+mv "$LOCAL_GSTACK.bak" "$LOCAL_GSTACK"
+```
+Tell user: "Sync failed — restored previous version at `$LOCAL_GSTACK`. Run `/gstack-upgrade` manually to retry."
+
 ### Step 5: Write marker + clear cache
 
 ```bash
@@ -191,9 +198,26 @@ When invoked directly as `/gstack-upgrade` (not from a preamble):
 
 1. Force a fresh update check (bypass cache):
 ```bash
-~/.claude/skills/gstack/bin/gstack-update-check --force
+~/.claude/skills/gstack/bin/gstack-update-check --force 2>/dev/null || \
+.claude/skills/gstack/bin/gstack-update-check --force 2>/dev/null || true
 ```
 Use the output to determine if an upgrade is available.
 
 2. If `UPGRADE_AVAILABLE <old> <new>`: follow Steps 2-6 above.
-3. If no output (up to date): tell the user "You're already on the latest version (v{version})."
+
+3. If no output (primary is up to date): check for a stale local vendored copy.
+
+Run the Step 2 bash block above to detect the primary install type and directory (`INSTALL_TYPE` and `INSTALL_DIR`). Then run the Step 4.5 detection bash block above to check for a local vendored copy (`LOCAL_GSTACK`).
+
+**If `LOCAL_GSTACK` is empty** (no local vendored copy): tell the user "You're already on the latest version (v{version})."
+
+**If `LOCAL_GSTACK` is non-empty**, compare versions:
+```bash
+PRIMARY_VER=$(cat "$INSTALL_DIR/VERSION" 2>/dev/null || echo "unknown")
+LOCAL_VER=$(cat "$LOCAL_GSTACK/VERSION" 2>/dev/null || echo "unknown")
+echo "PRIMARY=$PRIMARY_VER LOCAL=$LOCAL_VER"
+```
+
+**If versions differ:** follow the Step 4.5 sync bash block above to update the local copy from the primary. Tell user: "Global v{PRIMARY_VER} is up to date. Updated local vendored copy from v{LOCAL_VER} → v{PRIMARY_VER}. Commit `.claude/skills/gstack/` when you're ready."
+
+**If versions match:** tell the user "You're on the latest version (v{PRIMARY_VER}). Global and local vendored copy are both up to date."