xce_failover_rotate reconnected with endpoint_fini+endpoint_init+endpoint_connect
but never re-bound ep->iomgr (reset by endpoint_init) nor re-armed the owner/
msg/err handlers + iomgr_monitor. endpoint_connect then dereferenced a NULL
iomgr (->ssl_ctx) → SEGV at netio.c:672 during live master failover. Added
xce_ctx_reconnect() in xcectx.c that mirrors xcecli_start's establishment
(without restarting iomgr/vtaskmgr or touching ctx->state); rotate delegates to
it. Found via live 3-node E2E. bug-610.
Live 3-node E2E revealed the reported 'Invalid argument' bug was still
reachable: after the primary dies, handle_disconnect leaves ctx.state=
XCE_CTX_ERR, so a FRESH xce_* call returns -EINVAL from the xceapi guard
before reaching a primary. The classifier mapped -EINVAL to TERMINAL, so the
loop bailed without rotating/recovering. decide() now detects the known-dead
ctx and treats it as a prompt reconnect cause (RETRY_NOW), surfacing the
distinct cluster-not-ready code on budget exhaustion, never -EINVAL.
Regression test: test_decide_known_dead_ctx_retries_not_terminal.
