# Lifecycle and State
This server runs over the MCP `stdio` transport. The client owns the connection: it starts the process, speaks JSON‑RPC over stdin/stdout, and eventually disconnects. This page explains how lifecycle events interact with in‑memory state, and how to make state durable when needed.
## Process Model
- One Node.js process per MCP connection.
- One SWI‑Prolog child process inside the Node process.
- Tools (e.g., `knowledge_base_assert`, `query_start`) operate against the single in‑memory knowledge base.
## Shutdown Behavior
- The server exits when:
- It receives `SIGINT` or `SIGTERM` (typical client shutdown), or
- The MCP client closes stdio (stdin stream emits `close`).
- On stdio close the server waits a very small grace (~25 ms) before exiting to allow any final responses to flush.
- The Prolog child is stopped cleanly before the Node process exits.
Why close on stdio? It prevents orphaned processes if a client crashes or terminates without sending signals. This aligns with typical MCP `stdio` server behavior.
## State Persistence
- State is **per connection**: asserted facts and rules live in memory for the duration of the connection only.
- When the connection ends (signals or stdio close), the in‑memory Knowledge Base is discarded, and a fresh Knowledge Base is created on next start.
This is the expected behavior for `stdio` MCP servers. Clients that rely on shared state should keep a single connection open for the duration of their workflow.
## Client Guidance
- Maintain a single long‑lived `stdio` connection while coordinating multiple tool calls.
- Do not close stdin immediately after sending a request; doing so signals disconnect and will end the server.
## Durable Knowledge Base (optional)
If you want state to survive restarts, use an explicit dump/restore pattern under the allowed directory `~/.swipl-mcp-server/`:
1. Save snapshot:
- Call `knowledge_base_dump` and write the result into a file in `~/.swipl-mcp-server/`.
2. Restore on startup:
- Either script your client to call `knowledge_base_load` for the snapshot file, or
- Replay facts via `knowledge_base_assert_many` after connection initialization.
Notes:
- The server enforces file path restrictions; only `~/.swipl-mcp-server/` is permitted for file operations.
- Avoid secrets or sensitive paths; data under the allowed directory is considered non‑sensitive for the purpose of this server.
## Troubleshooting
- “Facts disappeared between calls”: ensure the MCP client kept the same `stdio` connection open and did not restart the server between calls.
- “Server exited before replying”: confirm the client did not close stdin immediately after sending a request. Keep the stream open until the response is received.
