Why

The agent ecosystem (Claude Desktop, Cursor, custom agents, …) has no shared answer for sovereign, ACL-gated storage. Every agent today bolts on its own DB, vector store, or secrets vault. Solid's pitch — user-owned data, queryable, access-controlled — is exactly what agents need, but the wire connecting them doesn't exist yet.

MCP (Model Context Protocol) is becoming that wire. If JSS speaks MCP, every MCP-compatible agent gets a sovereign data layer for free, with WAC, WebIDs, and Nostr identities all already in place.

Thesis statement: "MCP needs a backend. Solid is the backend."

This is the proposed v0.0.200 capstone — completing the feature-development phase before consolidation.

What

```bash
jss start --mcp # exposes /mcp endpoint speaking MCP
```

Initial tools

Tiny surface to start; expand once the foundation is in:

Deferred: `query` (SPARQL or JSON-LD frame), `delete_resource`, `patch_resource`.

Auth

Reuse existing JSS layers — no new auth code:

• WebID-OIDC + DPoP — for Claude Desktop and other browser-OIDC agents
• NIP-98 — for Nostr-native agents
• Bearer token — for headless agents / CI

The MCP server enforces WAC the same way every other JSS endpoint does. `acl:agent did:agent:claude` can grant a specific agent specific resources. `acl:agentClass` with a new `acl:Agent` term could grant agent-class-wide access.

Wire format

MCP supports stdio, HTTP+SSE, and WebSocket transports. HTTP+SSE is the natural fit — JSS already serves HTTP, and SSE composes with the existing notification infrastructure. Stdio is irrelevant (JSS is a long-running daemon).

Scope estimate

~500 lines. The protocol is thin, JSS already has all the backend primitives. The work is an adapter layer:

• MCP handshake (initialize, list_tools, capabilities)
• Tool dispatch (route MCP tool calls to existing JSS internals)
• SSE event stream wrapping the WS notification pipe

Why it's distinctive

• No other Solid server has this
• No other MCP server has WAC, WebID, or sovereign storage
• The combination is what's unique — Solid's strength (data sovereignty) becomes MCP's missing piece

Acceptance

• `jss start --mcp` exposes `/mcp` endpoint
• Claude Desktop can register the endpoint as an MCP server and read/write a resource
• WAC applies: agent without `acl:Write` gets 403 on `write_resource`
• `subscribe` emits events on resource changes via SSE
• Tested end-to-end with at least one external MCP-compatible client
• `docs/mcp.md` covers wiring up Claude Desktop / generic MCP clients

Out of scope (for v0.0.200)

• `query` tool (deferred to v0.0.201+)
• Agent-class WAC term (`acl:Agent`) — proposed but not blocking
• MCP "prompts" or "resources" surface (we expose tools first)
• Local LLM hosting / inference inside JSS