fix(agent): stop double-loading .claude/skills as synthetic plugins

[MattPua]

Problem

Skills in .claude/skills showed up twice in the session skill list: once bare (e.g. canvas-templates) and once under a synthetic plugin prefix (e.g. repo-skills-<hash>:canvas-templates). Same for ~/.claude/skills under user-skills:.

Changes

The Claude Agent SDK already auto-loads ~/.claude/skills and <repoPath>/.claude/skills natively as @skills-dir plugins. discover-plugins.ts was additionally symlinking those same directories into synthetic user-skills/repo-skills-<hash> plugins, so every skill loaded twice under two different names. Removed discoverUserSkills/discoverRepoSkills — only sources the SDK can't see on its own (marketplace-installed plugins, the user's Codex skills dir) still need manual discovery.

How did you test this?

• npx vitest run packages/workspace-server/src/services/agent/discover-plugins.test.ts — updated tests pass.
• pnpm --filter @posthog/workspace-server typecheck — no new errors (2 pre-existing unrelated failures confirmed present on main too).
• biome check on touched files — clean.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 67dbff7.}