Include manifestless plugin directories in the package census #442

🤖 Generated by the Agentic Engineer

Problem

An on-disk plugins/ child with an agent but no plugin.json is invisible to the orphan checks because they enumerate only existing plugin.json files. The package gate can report lockstep despite an incomplete unlisted plugin directory.

Proposed direction

Observe the complete direct plugin-directory inventory before validating manifest membership. Require each package directory to have the supported manifests and a unique matching marketplace/catalogue identity.

Acceptance criteria

• A manifestless or unlisted plugin child fails with a package-census diagnostic.
• Complete listed plugins remain valid.
• Linked roots and failed or partial directory observations remain refused.
• No untracked consumer resource is silently counted or adopted.

Size: S. Part of #38.