pstack skills disappear in other repos/worktrees until reinstall (cache sha churn + per-window prune race) #789

Symptom

pstack skills (/poteto-mode, /how, /bro, …) often don't show up in Cursor windows opened on other repos or git worktrees. Uninstalling and reinstalling pstack brings them back, until the next time. Other plugins from this monorepo (cursor-team-kit, gmail, google-calendar, google-drive, x) share the same cache key, so they are probably affected too. pstack is the one I notice because I use its slash commands all day.

Environment

• Cursor 3.27.12 (also seen on 3.26.x), macOS, Apple silicon, Glass layout
• pstack 0.15.30 from the cursor-public marketplace
• Usually 2 or 3 windows open at once, each on a different repo or worktree

What the logs and local state show

1. The cache key changes almost daily. Plugins from this repo are cached at ~/.cursor/plugins/cache/cursor-public/<plugin>/<monorepo commit sha>/. Over the last 6 days my windows picked up six different shas (d457567, ddf824a, 111cf6a, 190d287, d1453c1, 9b93e81), because any commit to the monorepo moves the pin, even one that only touches a third-party plugin.
2. Every window installs at the same moment. When a new sha arrives, each open window logs loadFromMarketplaceSource: Plugin missing from cache, installing: pstack within the same second and clones into the same directory. On 2026-10-22 16:02:11 and 2026-10-23 18:42:08/12 this happened in 2 to 3 windows at once.
3. Each load deletes the other versions. In cursor-agent-exec, after a plugin loads, pruneOldVersions({…, keepVersions:[e.version]}) removes every other sha directory. A window that loaded the previous sha keeps paths into a directory another window just deleted.
4. A failed load leaves a plugin with no skills. On a load error, loadFromMarketplaceSource records the plugin with loadError and skills: []. It still counts as installed but shows no skills until the window reloads. I saw concurrent-install collisions on other marketplace plugins, logged as Cursor plugin load error: gmail@4bf3e08…: EEXIST: file already exists, mkdir …/.cursor-plugin, gmail@4bf3e08…: ENOENT … open …/.cache-complete, and agentmail@aebd765…: ENOENT … unlink …/.mcp.json in two windows in the same millisecond.
5. The installed-plugin cache is stored per workspace. globalStorage/state.vscdb has one cursor.plugins.installedIds.<teamId>|<workspace uri> key per folder (54 for me), and every git worktree counts as a new workspace. The lists differ a lot: my main checkout has 17 plugin ids, while worktrees and repos I opened before installing have 4 to 8. The renderer hydrates this on window open (_hydrateInstalledPluginIdsFromStorage).
6. Backend misses. marketplace listEnabledPlugins failed … treating source as unavailable appears 114 times in my logs over about 2 weeks. A window that opens during one loads no marketplace plugins at all until it reloads.

Likely cause

A per-window cache of a shared on-disk directory, a pin that moves daily, and prune-on-load, with no lock between windows. Whichever window installs or prunes first can leave the other windows with a deleted path or a half-written directory. Items 5 and 6 explain why it shows up in "some other repo" and not everywhere at once. I haven't caught the slash menu missing pstack in the same window as a logged error, so the exact trigger is inferred from logs and code, not observed.

Workaround

Developer: Reload Window (or a full quit) in the affected window usually brings the skills back without reinstalling.

Asks

• Pin the cache per plugin (version or tree hash of pstack/) instead of the monorepo commit, so an unrelated commit doesn't force a reinstall.
• Lock or atomically rename (tmp dir → final path) when installing into the cache, and don't prune a version another window still has loaded.
• When a plugin load fails, retry or surface the error instead of silently keeping the plugin with skills: [].

Related: #136 (install, enable and cache lifecycle docs), #527 (disable-model-invocation and the / palette), and the forum thread on skills not showing until restart or a new repo.