Correct PROTOCOL_VERSION comment for harness per-scenario default

When --spec-version is omitted, the conformance harness picks the version
per-scenario (LATEST_SPEC_VERSION for active scenarios, DRAFT_PROTOCOL_VERSION
for draft-only ones), not a flat LATEST_SPEC_VERSION. The variable is still
log-only today, but the stateless 2026 client path will branch on it.

Author: maxisbey

.github/actions/conformance/client.py

@@ -7,8 +7,9 @@
     - MCP_CONFORMANCE_SCENARIO env var -> scenario name
     - MCP_CONFORMANCE_CONTEXT env var -> optional JSON (for client-credentials scenarios)
     - MCP_CONFORMANCE_PROTOCOL_VERSION env var -> spec version the harness mock
-      server is speaking (e.g. "2025-11-25", "2026-07-28"). Always set; defaults
-      to the harness's LATEST_SPEC_VERSION when --spec-version is omitted.
+      server is speaking (e.g. "2025-11-25", "2026-07-28"). Always set; when
+      --spec-version is omitted the harness picks per-scenario (LATEST_SPEC_VERSION
+      for active scenarios, DRAFT_PROTOCOL_VERSION for draft-only ones).
     - Server URL as last CLI argument (sys.argv[1])
     - Must exit 0 within 30 seconds
 
@@ -54,10 +55,11 @@
 logger = logging.getLogger(__name__)
 
 #: Spec version the harness is running this scenario at (e.g. "2025-11-25",
-#: "2026-07-28"). The harness always sets this (it falls back to its own
-#: LATEST_SPEC_VERSION when --spec-version is omitted), so None means we were
-#: invoked outside the harness. Handlers that need to take the stateless 2026
-#: path will branch on this once the SDK has one; today it is logged only.
+#: "2026-07-28"). The harness always sets this (when --spec-version is omitted
+#: it picks per-scenario: LATEST_SPEC_VERSION for active scenarios,
+#: DRAFT_PROTOCOL_VERSION for draft-only ones), so None means we were invoked
+#: outside the harness. Handlers that need to take the stateless 2026 path will
+#: branch on this once the SDK has one; today it is logged only.
 PROTOCOL_VERSION: str | None = os.environ.get("MCP_CONFORMANCE_PROTOCOL_VERSION")
 
 # Type for async scenario handler functions