[php-sdk] [Server] Connections to Github Copilot CLI time out on subscriptions/listen

## Observed symptom [Server] Connections to Github Copilot CLI time out on subscriptions/listen **Describe the bug** Github Copilot CLI (version 1.0.85 and above) fails to connect to stateless MCP server. Authentication is successful but the subsequent `subscriptions/listen` request never resolves, instead timing out after 10000 ms. Adding `@obflush` before the `flush` on line 83 of `StatelessResponder` resolves this issue. **To Reproduce** Steps to reproduce the behavior: 1. Run a stateless MCP server with default settings 2. Add an MCP server using Github Copilot CLI version ^1.0.85 3. Authenticate the server 4. The server will successfully authenticate but the connection will fail with a timeout error ## Environment GitHub modelcontextprotocol/php-sdk #516 ## Trigger / context Public GitHub report in modelcontextprotocol/php-sdk (FRESH_7D). ## Source evidence - https://github.com/modelcontextprotocol/php-sdk/issues/516 (2026-09-29T13:25:38Z) — evidence_class: PRIMARY_ISSUE_REPORT — #516 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T10:42:44.319212Z - scout_id: C9341ae1313 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.