McpServerConnection starts the session's server lazily through
PrepareProcessAsync, applies the call timeout, reports exits with the
stderr tail and restarts on the next call, stops when idle, and supports
StopAsync (reusable) and idempotent DisposeAsync. McpTool exposes a
catalogue entry as an ITool and maps results with McpResultMapper.
Spec change (ยง5, Decisions): ModelContextProtocol.Core 2.2.0 does not send
notifications/cancelled when a request's token fires (verified against the
fake server), so calls go out through SendRequestAsync with their own
request id and the connection sends notifications/cancelled itself on abort
and timeout. Also documents exit detection, StopAsync vs DisposeAsync and
JSON-RPC errors as ordinary error results, per the plan.
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