* fix(mcp): skip task servers whose discovery failed instead of dropping all tools
Per-server discovery replaced a failed or timed-out server with an empty
tool list. For a server with task_toolsets, _configure_task_tools_for_server
then reported submit/status/cancel as missing and raised
McpTaskConfigurationError, which get_mcp_tools re-raises, so the tools of
every healthy server were discarded and the cache was never published:
each agent build rediscovered every server.
load_server_tools now returns None for a failed discovery, distinct from a
server that answered with zero tools, and the wrapping loop skips such
servers before task-toolset validation. A server that answers without its
configured raw tools still raises as a configuration error.
* docs(changelog): reference #6481
* docs(mcp): name the cache-reset endpoint as a task-server recovery path
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>