fix(mcp): boot stdio server when invoked via cavemem mcp

[LoganBresnahan]

Summary

• cavemem mcp exits silently without ever connecting an MCP stdio transport.
• Root cause: the CLI's mcp command does await import('@cavemem/mcp-server') expecting the import side-effect to start the server, but main() is guarded behind isMainEntry(), which returns false for dynamic imports.
• Fix: export main() and call it explicitly from the CLI.

Repro

# Expected: stays running, serves JSON-RPC over stdio.
# Actual:   exits 0 immediately, transport never connects.
cavemem mcp

Or, with an explicit MCP initialize handshake:

printf '%s\n' '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test","version":"0"}}}' \
  | cavemem mcp
# (no response — server never started)

Any host that connects to cavemem mcp over the standard MCP stdio transport sees zero tools.

Root cause

apps/mcp-server/src/server.ts guards main() behind an isMainEntry() check:

if (isMainEntry()) {
  main().catch(...);
}

function isMainEntry(): boolean {
  // import.meta.url = .../mcp-server/dist/server.js
  // process.argv[1]  = .../cli/dist/index.js  (when spawned via `cavemem mcp`)
  return import.meta.url === pathToFileURL(realpathSync(argv)).href;
}

apps/cli/src/commands/mcp.ts (before this PR):

// Delegate: importing runs main() via the server module.
await import('@cavemem/mcp-server');

The comment is wrong — dynamic import never runs main() because isMainEntry() returns false when the module is loaded through the CLI bundle. As a result, the stdio transport is never connected.

Fix

Export main from the server module and have the CLI call it explicitly. The isMainEntry() guard is preserved so the cavemem-mcp bin (direct invocation) still works.

Changes

• apps/mcp-server/src/server.ts: async function main → export async function main
• apps/cli/src/commands/mcp.ts: import { main } and call it
• apps/mcp-server/test/exports.test.ts: regression test pinning the main export
• .changeset/fix-mcp-cli-import.md: patch changeset for cavemem + @cavemem/mcp-server

Test plan

• pnpm typecheck passes
• pnpm lint (biome) passes
• pnpm build produces a cavemem dist whose dist/index.js calls await import('./server-XXXX.js').main() and whose server chunk emits export { buildServer, main }
• apps/mcp-server tests pass (8 incl. new export pin)
• apps/cli tests pass (4)
• After packing + global install, cavemem mcp responds to a JSON-RPC initialize request with a valid handshake (server stays alive, lists 4 tools)
• cavemem-mcp bin still works when invoked directly (regression check on the isMainEntry() path)