fix(initialize scenario): return 202 No Content for notifications (closes #274)

[adityachilka1]

Closes #274.

The bug

The initialize scenario test server had a fall-through branch for post-negotiation
requests:

// src/scenarios/client/initialize.ts:78~90
if (request.method === 'initialize') {
  this.handleInitialize(request, res);
} else if (request.method === 'tools/list') {
  this.handleToolsList(request, res);
} else {
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({ jsonrpc: '2.0', id: request.id, result: {} }));
}

When the client POSTs notifications/initialized (no id field), that
falls into the else branch and the server replied with
{"jsonrpc":"2.0","id":undefined,"result":{}}. That violates the transport
spec (2025-11-25 § 2.1, point 4):

If the input is a JSON-RPC response or notification:

• If the server accepts the input, the server MUST return HTTP status
  code 202 Accepted with no body.

Strict clients that reject 200-with-body-for-notification were failing against
the scenario.

The fix

Insert a branch for request.id == null before the 200-placeholder else:

         } else if (request.method === 'tools/list') {
           this.handleToolsList(request, res);
+        } else if (request.id == null) {
+          res.writeHead(202);
+          res.end();
         } else {
           res.writeHead(200, { 'Content-Type': 'application/json' });

== null catches both id: null (explicitly passed) and id-omitted (the
JSON.parse result for a notification payload).

Verification

npm run typecheck  # tsgo --noEmit
npm run lint       # eslint + prettier

Both pass clean.

No other behavioral changes

• Initialize and tools/list flows are untouched.
• Requests with a present id still hit the 200-placeholder else branch.
• Only the true notification case (e.g. notifications/initialized) changes -
  from 200+JSON to 202+empty.

[nbarbettini]

Can this condition be made more explicit: check that it is in fact a notifications/initialized notification and not something else?

[adityachilka1]

Good call. Narrowed the condition to check the exact method (notifications/initialized) rather than any id-less payload. Anything else - stray notifications, malformed requests - falls through to the existing else branch, so the prior behavior for those cases is preserved.

Force-pushed - single-commit PR, one-line diff from the previous revision. Typecheck and lint clean.

[nbarbettini]

This LGTM 👍