launch: give RL islands the env Megatron actually wants (re-land #63 on main) - #68
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Megatron's argument validation refuses tensor or context parallelism without it. The SSH harness already sets it per container; the sky/Modal island task did not, so the first TP4 island (Qwen3.6-27B on 8xH100) failed in parse_args before loading anything.
The island envs forced the unfused attention backend. The learner already passes --attention-backend per recipe and Megatron sets the three NVTE variables from that flag in every actor, so the pin was redundant for the generic provider and fatal for the flash recipes: the Qwen3.6-27B island asserted 'NVTE_FLASH_ATTN set to 0, but expected 1' at model construction.
The two commits on this branch had no OpenSpec change of their own. Records them under the sky-rl-island-runtime capability that fix-sky-island-ray-stop introduces: the island's env must satisfy Megatron's precondition for TP>1 and must not pin an attention backend the learner did not choose. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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#63 was merged into its stacked base branch after that branch had already landed on main, so its changes never reached main. This PR carries the same branch onto main; its diff against main is exactly #63's changes.
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