feat(mcp): start MCP servers in bounded parallel batches - #358

What

MCP server startup in McpManager.initialize() was strictly serial: each configured server paid its own spawn + handshake before the next one started, so startup time was the sum over all servers.

This starts servers in batches of 5 (Promise.allSettled), which cuts total startup to roughly 1/5 for typical configs while keeping the process/memory peak bounded — unlike launching every server at once.

Change

packages/core/src/mcp/mcp-manager.ts (+9/-2):

const entries = Object.entries(servers);
const CONCURRENCY = 5;
for (let i = 0; i < entries.length; i += CONCURRENCY) {
  if (this.disposed) break;
  const batch = entries.slice(i, i + CONCURRENCY);
  await Promise.allSettled(batch.map(([name, config]) => this.connectServer(name, config)));
}

Promise.allSettled also isolates failures: previously an exception thrown while connecting one server aborted the loop and left every later server unstarted. Per-server status reporting and crash handling (onServerCrash) are unchanged.

Why this is safe

connectServer mutates clients / tools / prompts / resources synchronously between its await points, and the namespaced-name reservation block contains no await, so concurrent callers cannot interleave and corrupt that state. The only observable difference is that status/log lines may now appear in a different order.

Tests

packages/core/src/tests/mcp-manager-parallel.test.ts (new, 2 tests, no child processes — connectServer is stubbed so the test exercises scheduling only):

• all 12 configured servers start, with peak in flight > 1 and <= 5;
• a disconnect() raised mid-startup starts no further batch.

Checked that the test has teeth: reverting the loop to the previous serial form makes the first test fail with expected overlapping connections, saw peak=1.

Verification (local, full CI equivalent)

npm run check (typecheck + eslint + prettier) · npm run build --workspace=@vegamo/deepcode-core · npm run bundle · npm run build:vscode · npm test — all pass (59 tests, 0 failures).

Overlap

Open PR #198 also edits mcp-manager.ts, but its hunks are disjoint from this one (import restructure + createMcpClient inside connectServer), so the two can land in either order.