From 1e1882851d3f66138cffa0351ac9d535a717189b Mon Sep 17 00:00:00 2001
From: Jeremiah Lowin <153965+jlowin@users.noreply.github.com>
Date: Mon, 20 Jul 2026 12:46:34 -0400
Subject: [PATCH] Keep the CLI URL proxy era-agnostic; monitor claimed-result
 resolution

---
 fastmcp_slim/fastmcp/cli/run.py             | 13 +++++++++----
 fastmcp_slim/fastmcp/client/mixins/tools.py |  9 +++++++--
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/fastmcp_slim/fastmcp/cli/run.py b/fastmcp_slim/fastmcp/cli/run.py
index 476c0267d..0d12f14c2 100644
--- a/fastmcp_slim/fastmcp/cli/run.py
+++ b/fastmcp_slim/fastmcp/cli/run.py
@@ -97,10 +97,15 @@ def create_client_server(url: str) -> Any:
         A FastMCP server instance
     """
     try:
-        import fastmcp
-
-        client = fastmcp.Client(url)
-        server = create_proxy(client)
+        # Hand `create_proxy` the URL rather than a pre-built `Client`. A Client
+        # target is treated as caller-configured and pinned, so its era would be
+        # fixed at construction — and since `Client` now defaults to `"auto"`,
+        # that would pin this proxy's upstream to the modern era and break
+        # handshake-era clients connecting to it (`ping`, server-initiated
+        # forwarding). Passing the URL lets the proxy mirror each front
+        # connection's negotiated era instead, so `fastmcp run <URL>` serves
+        # both eras.
+        server = create_proxy(url)
         return server
     except Exception as e:
         logger.error(f"Failed to create client for URL {url}: {e}")
diff --git a/fastmcp_slim/fastmcp/client/mixins/tools.py b/fastmcp_slim/fastmcp/client/mixins/tools.py
index 418976f69..d52e90cb9 100644
--- a/fastmcp_slim/fastmcp/client/mixins/tools.py
+++ b/fastmcp_slim/fastmcp/client/mixins/tools.py
@@ -230,8 +230,13 @@ class ClientToolsMixin:
             else:
                 # A claimed extension result (SEP-2133): resolve it through the
                 # owning extension's resolver into an ordinary CallToolResult.
-                result = await self._resolve_claimed_result(
-                    name, driven, read_timeout_seconds
+                # Resolution issues further session requests of its own (result
+                # validation lists tools; a resolver may make more), so it needs
+                # the same session monitoring as the calls above — otherwise a
+                # transport-level failure can kill the session runner while this
+                # await waits forever.
+                result = await self._await_with_session_monitoring(
+                    self._resolve_claimed_result(name, driven, read_timeout_seconds)
                 )
 
             # Reflect tool-level errors on the span so callers see ERROR