remote-client: isSessionNotFound is tightly coupled to SDK error shape

[OpenCodeEngineer]

Found while reviewing #8.

src/daemon/remote-client.ts:145-151:

function isSessionNotFound(err: unknown): boolean {
  if (!err || typeof err !== 'object') return false;
  const code = (err as {code?: unknown}).code;
  return code === 404;
}

This relies on the SDK's StreamableHTTPError.code being the HTTP status. If the SDK ever changes that field — e.g. to the JSON-RPC error code (-32001) or wraps the error in another type — the retry path silently regresses and users see a raw "Session not found" instead of the transparent reconnect that sticky sessions are designed to deliver.

The current test fixture matches this exact shape so a regression wouldn't be caught.

Suggested fix:

import {StreamableHTTPError} from '@modelcontextprotocol/sdk/client/streamableHttp.js';

function isSessionNotFound(err: unknown): boolean {
  if (err instanceof StreamableHTTPError) {
    return err.code === 404 || /Session not found/i.test(err.message);
  }
  return false;
}

Add a test case where the server returns a JSON-RPC -32001 envelope without an HTTP 404 so this contract is locked in.