refactor(agent)!: remove packages, manifests, and fork

[Yevanchen]

Parent

• feat(platform): pivot Mosoo to an API-first managed Agent runtime #546

What to build

Remove the Agent distribution and portability product surface:

• Agent Package import and export.
• Portable Agent manifests and manifest-version negotiation.
• Agent Fork, including target-Type Fork behavior.
• Package upload/download, validation, storage, UI, CLI, documentation, generated contracts, and tests.
• Compatibility parsers, format conversion, and tombstone endpoints whose only purpose is accepting the removed package format.

Do not replace these concepts with another marketplace or archive format.

Retain only the reusable configuration required by the Session API:

• A Workspace-private saved Agent configuration.
• Immutable Agent revisions; updating a saved configuration creates a new revision.
• Every Session records the exact revision it resolves.
• Managed Agent slugs resolve to Mosoo-owned immutable revisions through the same execution contract.
• Creating or updating a private revision does not require Publish.

A private Agent revision is a runtime configuration reference, not a portable package or distribution unit. Its active API representation contains only fields consumed by execution; it does not preserve package metadata, public visibility, import provenance, or Fork lineage.

Historical Sessions, messages, artifacts, usage, and frozen execution provenance remain readable. That does not require keeping package operations alive.

Production D1 remains append-only. Any physical removal or rewrite of existing production columns requires separate explicit approval, a backup, verification queries, and a rollback plan. Inert historical storage is acceptable temporarily; reachable compatibility code is not.

Billing, balances, subscriptions, invoices, and BYOK settlement are non-goals.

Acceptance criteria

• Agent Package import/export routes, GraphQL mutations, services, jobs, contracts, UI, CLI commands, documentation, generated clients, and active tests are removed rather than hidden.
• Agent Fork and all target-Type or Fork-lineage behavior are removed.
• No reachable compatibility parser, old-format converter, or package tombstone remains.
• Active product and public contracts contain no portable Agent manifest or package-format version.
• A Workspace can create a private Agent configuration and receive immutable revision 1 without Publish.
• Updating that configuration creates immutable revision 2 without mutating revision 1.
• Sessions can start explicitly from revision 1 and revision 2, and each Session snapshot retains the correct revision.
• A managed Agent slug and private Agent revision enter the same Session execution path.
• Existing historical Sessions and artifacts remain readable after package features are removed.
• Repository-wide searches find no reachable Import, Export, Package, Manifest, or Fork product path; unavoidable historical migration identifiers are documented.
• Tests cover authorization, immutable revision creation, revision pinning, and removal of package/fork entrypoints.
• No billing or BYOK settlement work is introduced.

Blocked by

• feat(api): add the durable Agent Session API #582 — the thin private configuration and immutable revision contract must be executable before the package lifecycle is removed.