Server-prefixed tool names are not unique across servers: server 'a'
exposing 'b_x' and server 'a_b' exposing 'x' both bind as 'a_b_x'. The
flatten step forwarded both declarations to the model, where the provider
silently keeps only one and the other server's tool becomes unreachable
with no diagnostic.
Deduplicate by bound name in enabled-server declaration order and drop
later duplicates with a warning.
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
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