fix: include required result members in 2026-07-28 mock responses (#341)

At the 2026-07-28 revision every server result must include resultType,
and cacheable results (server/discover, tools/list, prompts/list,
resources/list, resources/templates/list, resources/read) must also
include ttlMs and cacheScope. The client-direction mock servers omitted
these, so a strictly-validating client was failed by the suite's own
non-conformant mock.

The shared stateless mock now stamps the missing members onto handler
results and its server/discover response (withRequiredDraftResultFields),
and the hand-rolled per-scenario servers set them explicitly or route
their fallbacks through the helper. The deliberately resultType-less
probe in sep-2322-client-request-state is unchanged. New tests pin the
response shapes.

src/scenarios/client/http-custom-headers.ts

@@ -276,6 +276,9 @@ export class HttpCustomHeadersScenario extends BaseHttpScenario {
       jsonrpc: '2.0',
       id: request.id,
       result: {
+        resultType: 'complete',
+        ttlMs: 0,
+        cacheScope: 'private',
         tools: [
           {
             name: 'test_custom_headers',
@@ -591,6 +594,7 @@ export class HttpCustomHeadersScenario extends BaseHttpScenario {
       jsonrpc: '2.0',
       id: request.id,
       result: {
+        resultType: 'complete',
         content: [{ type: 'text', text: 'Custom headers test completed' }]
       }
     });
@@ -760,6 +764,9 @@ export class HttpInvalidToolHeadersScenario extends BaseHttpScenario {
       jsonrpc: '2.0',
       id: request.id,
       result: {
+        resultType: 'complete',
+        ttlMs: 0,
+        cacheScope: 'private',
         tools: [
           // ── Valid tool (should be kept by client) ──
           {
@@ -938,6 +945,7 @@ export class HttpInvalidToolHeadersScenario extends BaseHttpScenario {
       jsonrpc: '2.0',
       id: request.id,
       result: {
+        resultType: 'complete',
         content: [{ type: 'text', text: 'Tool call received' }]
       }
     });