Two separate schema issues blocked `/plugin marketplace add ./plugins`
followed by `/plugin install semantica@semantica-local`:
1. `marketplace.json` was missing the required top-level `owner` object.
Claude Code rejects with: `owner: Invalid input: expected object,
received undefined`.
2. `plugin.json` declared `"agents": "./agents"` (string), but Claude
Code's manifest schema rejects non-array `agents` with:
`Validation errors: agents: Invalid input`. Auto-discovery from
the default `agents/` directory works when the field is omitted,
provided agents are flat `<name>.md` files with frontmatter (Claude
Code's subagent convention) rather than `<name>/AGENT.md`
subdirectories.
Changes:
- add `owner` object to `marketplace.json`
- drop `agents` field from `plugin.json` (falls back to auto-discovery)
- rename `agents/<name>/AGENT.md` -> `agents/<name>.md` (frontmatter
content is unchanged, just the path)
After this, the documented local-install flow succeeds end-to-end.
Serge