fix: skip MCP preflight content-type probe on reconnect when already ready (#40604)

Closes #40366.

Salvaged from #40548; re-verified on main, tightened, tested.

Co-authored-by: mohamedorigami-jpg <mohamedorigami-jpg@users.noreply.github.com>

tools/mcp_tool.py

@@ -1800,7 +1800,12 @@ class MCPServerTask:
             # before surfacing an opaque CancelledError. Probing here — once,
             # outside the SDK task group — fails fast and non-retryably with
             # an actionable message, mirroring the URL-validation path above.
-            if config.get("transport") != "sse":
+            # Skip the probe when _ready is already set: that only happens
+            # after a prior successful connect, so this run() invocation is a
+            # reconnect (OAuth recovery / manual refresh). The endpoint was
+            # already validated once; re-probing burns a redundant network
+            # round-trip against a known-good server on every reconnect.
+            if config.get("transport") != "sse" and not self._ready.is_set():
                 try:
                     _probe_headers = dict(config.get("headers") or {})
                     await self._preflight_content_type(