- Add module-level _unwrap_exception_group (ported from
hermes_cli/mcp_config.py, adapted): handles nested groups, prefers
non-cancellation leaves over the CancelledErrors anyio sprays across
sibling tasks, and re-raises KeyboardInterrupt/SystemExit leaves.
- Add _classify_mcp_failure(exc) -> 'permanent'|'transient'.
Permanent: auth 401/403, NonMcpEndpointError, InvalidMcpUrlError,
FileNotFoundError/ENOENT on the stdio command. Transient: everything
else (network/EOF/ClosedResource/TaskGroup drops). Permanent failures
park immediately without burning the retry ladder — every retry
against a missing binary or a revoked credential hits the same wall.
- Every log site in run() and the keepalive failure log now logs the
unwrapped root cause as 'TypeName: message', so a dead stdio pipe
says 'BrokenPipeError' instead of the opaque
'unhandled errors in a TaskGroup (1 sub-exception)' (and empty
str(exc) dead-pipe errors are no longer blank).
