feat: add subscription listen streams (SEP-2575) (#1000)

* feat: add subscription listen streams

* refactor: reuse legacy request helper

.github/workflows/conformance.yml

@@ -85,79 +85,6 @@ jobs:
           echo "draft conformance server did not become ready" >&2
           exit 1
 
-      # useful for enforcing partial conformance for SEP-2575.
-      # when `server-stateless` is removed from `expected-failures-2026-07-28.yaml`,
-      # this step can be removed.
-      - name: Run SEP-2575 discovery contract
-        run: |
-          endpoint=http://127.0.0.1:8002/mcp
-          common_headers=(
-            -H "Content-Type: application/json"
-            -H "Accept: application/json, text/event-stream"
-            -H "Mcp-Method: server/discover"
-          )
-
-          discover_response="$(
-            curl --fail-with-body --silent --show-error \
-              "${common_headers[@]}" \
-              -H "MCP-Protocol-Version: 2026-07-28" \
-              --data '{
-                "jsonrpc": "2.0",
-                "id": "discover",
-                "method": "server/discover",
-                "params": {
-                  "_meta": {
-                    "io.modelcontextprotocol/protocolVersion": "2026-07-28",
-                    "io.modelcontextprotocol/clientInfo": {
-                      "name": "conformance-workflow",
-                      "version": "1.0.0"
-                    },
-                    "io.modelcontextprotocol/clientCapabilities": {}
-                  }
-                }
-              }' \
-              "$endpoint"
-          )"
-          jq -e '
-            .result.resultType == "complete" and
-            (.result.supportedVersions | index("2026-07-28") != null) and
-            (.result.capabilities | type == "object") and
-            (.result.serverInfo.name | type == "string") and
-            .result.ttlMs == 0 and
-            .result.cacheScope == "private"
-          ' <<<"$discover_response"
-
-          status="$(
-            curl --silent --show-error \
-              --output /tmp/unsupported-version.json \
-              --write-out "%{http_code}" \
-              "${common_headers[@]}" \
-              -H "MCP-Protocol-Version: 2099-01-01" \
-              --data '{
-                "jsonrpc": "2.0",
-                "id": "unsupported",
-                "method": "server/discover",
-                "params": {
-                  "_meta": {
-                    "io.modelcontextprotocol/protocolVersion": "2099-01-01",
-                    "io.modelcontextprotocol/clientInfo": {
-                      "name": "conformance-workflow",
-                      "version": "1.0.0"
-                    },
-                    "io.modelcontextprotocol/clientCapabilities": {}
-                  }
-                }
-              }' \
-              "$endpoint"
-          )"
-          test "$status" = "400"
-          jq -e '
-            .id == "unsupported" and
-            .error.code == -32022 and
-            .error.data.requested == "2099-01-01" and
-            (.error.data.supported | index("2026-07-28") != null)
-          ' /tmp/unsupported-version.json
-
       - name: Run 2026-07-28 server suite
         run: |
           npx -y "@modelcontextprotocol/conformance@${DRAFT_CONFORMANCE_VERSION}" server \