[Docs][Examples][CI] Document and gate the 2026-07-28 lifecycle (#457)

docs/stateless-lifecycle.md walks the revision end to end - per-request
_meta, server/discover, multi round-trip requests, caching and subscriptions
- and a runnable example on each side shows what that looks like in code.

CI matrixes both conformance roles over both revisions. --spec-version is
cumulative across the dated revisions, so 2025-11-25 covers the two before
it; 2026-07-28 is not cumulative with them and needs its own run against its
own baseline. The runner is pinned so a PR only goes red for reasons in the
PR, and conformance-weekly tracks the moving target instead - on both
revisions, since the draft scenarios ship only on the alpha dist-tag.

The Inspector cannot reach a modern-lifecycle server (it opens with
initialize), so the example is covered by integration tests instead: one
drives it with hand-built HTTP the way a conforming client would, one drives
it with this SDK's client, and one drives the single endpoint from both eras.

docs/server-client-communication.md

@@ -1,6 +1,13 @@
 # Client Communication
 
-MCP supports various ways a server can communicate back to a server on top of the main request-response flow.
+MCP supports various ways a server can communicate back to a client on top of the main request-response flow.
+
+> **Protocol revision `2026-07-28`.** This page describes the handshake era, where a server sends its own
+> JSON-RPC requests to the client. The modern lifecycle removed that: sampling, elicitation and roots are
+> carried back inside the *result* instead, and `ClientGateway::sample()`, `elicit()` and `listRoots()`
+> raise a `LogicException` there. Logging and progress still work as described below — they simply travel
+> on the request's own response stream, and the client opts into each. See
+> [The 2026-07-28 Lifecycle](stateless-lifecycle.md).
 
 ## Table of Contents