graph: pass netId (not netDev) to ncclTopoGetIntermediateRank in PXN level 1

[EylonKrause]

Description

In ncclTopoGetNetDev, the NCCL_P2P_PXN_LEVEL=1 branch calls:

NCCLCHECK(ncclTopoGetIntermediateRank(comm->topo, rank, *dev, proxyRank));

passing *dev — the raw network device index just assigned from netDev. But ncclTopoGetIntermediateRank's third parameter is an int64_t netId, consumed as a topology id via ncclTopoIdToIndex(system, NET, netId, ...). A NET node's id is netId = NCCL_TOPO_ID(systemId, dev) = (systemId << 56) | dev, which differs from the bare dev whenever systemId != 0 (a multi-system / MNNVL fused topology). In that case the lookup finds no matching NET node and returns ncclInternalError, which propagates out of ncclTopoGetNetDev and breaks proxy / intermediate-rank resolution during initialization. On a single-system topology systemId == 0 makes netId == dev, which masks the bug. The sibling call earlier in the function and the entire PXN_LEVEL=2 branch already pass netId.

This also removes a latent NULL dereference: a few lines above, *dev is written under if (dev) *dev = netDev;, but the ncclTopoGetIntermediateRank call dereferenced *dev unconditionally; callers may pass dev == NULL on this path.

Related Issues

None.

Changes & Impact

• src/graph/search.cc (ncclTopoGetNetDev, PXN level 1): pass netId instead of *dev to ncclTopoGetIntermediateRank, matching the sibling call site and the PXN level 2 branch. Single-system behavior is unchanged (netId == dev there); the fix corrects intermediate-rank resolution on multi-system / MNNVL topologies and removes the unguarded *dev deref. Non-breaking.

Performance Impact

None.

Testing

• Builds clean with make src.build.
• Verified by inspection against the two correct call sites (the sibling call and the PXN level 2 branch both pass netId) and the NCCL_TOPO_ID(systemId, dev) definition. The failure requires a multi-system / MNNVL topology with NCCL_P2P_PXN_LEVEL=1, which cannot be reproduced on a single-GPU machine; on single-system topologies systemId == 0, so the change is behavior-preserving there.