The Claude plugin manifest allows `commands`, `slash-commands`, and `skills`
to be either a single string or an array of strings — documented under
https://code.claude.com/docs/en/plugins-reference#path-behavior-rules and
used by real marketplace plugins such as addyosmani/agent-skills whose
plugin.json declares `"commands": ["./.claude/commands", "./commands"]`.
`resolvePluginDir` in `packages/coding-agent/src/discovery/claude-plugins.ts`
typed those manifest fields as `string` only, so array-shaped values were
silently dropped: no items loaded, no warning surfaced. Slash commands
(`spec`, `plan`, `build`, `test`, `review`) never appeared in the picker.
Normalize `string | string[]` at the resolver, load every in-root entry,
and emit one out-of-plugin-root warning per bad entry so misconfigured
paths remain observable. Skills and slash-command loaders now fan out over
the resolved directory list and merge warnings from all sources.
Fixes#4609
roboomp
d9ef874e2b