"What is the reason for high visiting in some day?"

Who does the reasoning here?

Three layers, three different jobs. Worth being precise about which one does what.

The investigation, four real MCP calls

Unedited. Including the one that failed.

SELECT toDate(start) AS date, count() AS visit_count
FROM sessions_v2 WHERE site_id = 101
  AND start >= '2026-08-01' AND start <= '2026-08-15'
GROUP BY todate(start)  ← lowercase, not the toDate() above
ORDER BY visit_count DESC LIMIT 1000

SELECT toDate(start) AS day, COUNT(*) AS session_count
FROM sessions_v2 WHERE site_id = 101
  AND start >= '2026-08-01' AND start <= '2026-08-15'
GROUP BY toDate(start) ORDER BY session_count DESC LIMIT 1000

SELECT referrer_source, COUNT(*) AS session_count
FROM sessions_v2 WHERE site_id = 101 AND toDate(timestamp) = '2026-08-05'
GROUP BY referrer_source ORDER BY session_count DESC LIMIT 1000

The same finding, visually

Both spike days — not just one — show Email newsletter's share roughly doubling against its own baseline.

The answer

Under the hood: Claude, MCP, and EKOS

The three-layer summary above is accurate but compressed. Here's what actually crosses the wire and runs inside ekos mcp serve for a single ekos_clickhouse_query call.

The transport: stdio, not a socket

ekos mcp serve --workspace analytics/ is one OS process. Claude Code launches it as a child process and talks to it over its stdin/stdout pipes — no port, no HTTP, no auth handshake beyond MCP's own initialize. The server's entire request loop is for line in stdin.lock().lines(): read one line, parse it as a JSON-RPC 2.0 object, dispatch on method, write exactly one response line to stdout, repeat. notifications/initialized is the one message that gets no reply, per the MCP spec — it's a notification, not a request. This is also why the process is disposable: it holds no session state between calls beyond what's on disk (the ledger, the compiled schema) — every tools/call opens what it needs fresh.

Inside one tools/call

The five internal stages in the diagram above are RFC 0056's own pipeline, unchanged from the CLI path (ekos clickhouse ask and the MCP tool share the same ask_clickhouse function — the only difference is which process calls it):

The gate is checked twice, not once

ekos_clickhouse_query only appears in tools/list's response when [clickhouse] enable-mcp-query = true is set — this workspace's ekos.toml opted in explicitly for this test. But the same flag is re-checked independently inside tools/call's dispatch, because an MCP client can call a tool by name directly without ever having listed it first. Both paths are load-bearing: hiding a tool from discovery isn't the same guarantee as refusing to run it.

Where the reasoning actually lives

Nothing in the five stages above has any memory of a previous call, and nothing in ekos mcp serve decides to retry. When Step 1's GROUP BY todate(start) failed, EKOS's only job was finished the moment it returned that ClickHouse error string as the tool's result. Every decision after that — noticing the failure, guessing the cause, rephrasing the question, deciding which table/column pairing to interrogate next based on what the previous real answer said — happened in the MCP client, reading the same JSON-RPC responses a human would read off this page. EKOS's local LLM is doing real work in every call (English → grounded SQL), but it is not the layer answering "what is the reason" — that question only gets answered by something outside this process chaining several of these calls together and comparing the results, which is the whole reason this page exists instead of a single query.

A gotcha this exact wiring hit before

Not from this session, but worth knowing if you extend this: ekos mcp serve's for line in stdin.lock().lines() loop runs directly inside main's #[tokio::main] runtime — it's never spawned onto its own task. ask_clickhouse's pipeline is async. Calling an async function from inside an already-running multi-thread Tokio runtime with a naive Runtime::new().block_on(...) panics: "Cannot start a runtime from within a runtime." The fix (already in place, not something this test needed to touch) branches on tokio::runtime::Handle::try_current(): bridge via tokio::task::block_in_place when already inside a runtime, build a throwaway one otherwise. No unit test in this codebase runs from inside an active Tokio runtime the way ekos mcp serve's real entry point does — this class of bug is only found by actually running the command, the same discipline this whole page's live MCP test follows rather than trusting cargo test alone.