feat(ce-update): add plugin version check skill and ce_platforms filtering (#532)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

plugins/compound-engineering/skills/ce-update/SKILL.md

@@ -0,0 +1,69 @@
+---
+name: ce-update
+description: |
+  Check if the compound-engineering plugin is up to date and fix stale cache if not.
+  Use when the user says "update compound engineering", "check compound engineering version",
+  "ce update", "is compound engineering up to date", "update ce plugin", or reports issues
+  that might stem from a stale compound-engineering plugin version. This skill only works
+  in Claude Code — it relies on the plugin harness cache layout.
+disable-model-invocation: true
+ce_platforms: [claude]
+---
+
+# Check & Fix Plugin Version
+
+Verify the installed compound-engineering plugin version matches the latest released
+version, and fix stale marketplace/cache state if it doesn't. Claude Code only.
+
+## Pre-resolved context
+
+The three sections below contain pre-resolved data. Only the **Plugin root
+path** determines whether this session is Claude Code — if it contains an error
+sentinel, an empty value, or a literal `${CLAUDE_PLUGIN_ROOT}` string, tell the
+user this skill only works in Claude Code and stop. The other two sections may
+contain error sentinels even in valid Claude Code sessions; the decision logic
+below handles those cases.
+
+**Plugin root path:**
+!`echo "${CLAUDE_PLUGIN_ROOT}" 2>/dev/null || echo '__CE_UPDATE_ROOT_FAILED__'`
+
+**Latest released version:**
+!`gh release list --repo Everyinc/compound-engineering-plugin --limit 30 --json tagName --jq '[.[] | select(.tagName | startswith("compound-engineering-v"))][0].tagName | sub("compound-engineering-v";"")' 2>/dev/null || echo '__CE_UPDATE_VERSION_FAILED__'`
+
+**Cached version folder(s):**
+!`ls "${CLAUDE_PLUGIN_ROOT}/cache/every-marketplace/compound-engineering/" 2>/dev/null || echo '__CE_UPDATE_CACHE_FAILED__'`
+
+## Decision logic
+
+### 1. Platform gate
+
+If **Plugin root path** contains `__CE_UPDATE_ROOT_FAILED__`, a literal
+`${CLAUDE_PLUGIN_ROOT}` string, or is empty: tell the user this skill requires Claude Code
+and stop. No further action.
+
+### 2. Compare versions
+
+If **Latest released version** contains `__CE_UPDATE_VERSION_FAILED__`: tell the user the
+latest release could not be fetched (gh may be unavailable or rate-limited) and stop.
+
+If **Cached version folder(s)** contains `__CE_UPDATE_CACHE_FAILED__`: no marketplace cache
+exists. Tell the user: "No marketplace cache found — this appears to be a local dev checkout
+or fresh install." and stop.
+
+Take the **latest released version** and the **cached folder list**.
+
+**Up to date** — exactly one cached folder exists AND its name matches the latest version:
+- Tell the user: "compound-engineering **v{version}** is installed and up to date."
+
+**Out of date or corrupted** — multiple cached folders exist, OR the single folder name
+does not match the latest version. Use the **Plugin root path** value from above to
+construct the delete path.
+
+**Clear the stale cache:**
+```bash
+rm -rf "<plugin-root-path>/cache/every-marketplace/compound-engineering"
+```
+
+Tell the user:
+- "compound-engineering was on **v{old}** but **v{latest}** is available."
+- "Cleared the plugin cache. Now run `/plugin marketplace update` in this session, then restart Claude Code to pick up v{latest}."