MCP 2026-07-28: subscriptions/listen is not implemented, so modern servers cannot push list or resource changes #4193

Summary

Modern-only servers cannot keep tools, prompts and resource updates current through the required opt-in stream mechanism.

Evidence (senpi main at the audit, 2026-10-24)

• C4 (missing, medium): Modern-only servers cannot keep tools, prompts and resource updates current through the required opt-in stream mechanism.
  • Evidence: packages/coding-agent/src/core/extensions/builtin/mcp/notifications.ts:106-115; resources.ts:45-52; notification-schemas.ts:57-85; no subscriptions/listen production sender in M/
  • Spec: spec 2026-07-28 docs/specification/2026-07-28/basic/patterns/subscriptions.mdx “Opening a Stream”, “Notification Filter”, “Acknowledgment”, “Receiving Notifications”

Expected

senpi opens a subscriptions/listen stream for servers that support it and opts into toolsListChanged/promptsListChanged/resourcesListChanged/resourceSubscriptions as it needs, handling the acknowledgment and subscription ids.

Acceptance

• A RED test that fails on current main first, then the fix.
• Legacy (2025-11-25 and earlier) servers behave as today.

Related

Follow-up of #3304 / #3309 from the MCP 2026-07-28 spec-sync audit. Headless elicitation: #4185.