chore: remove prefix-cache-salt and reset-prefix-cache config flags

[samsja]

Summary

• Drop the orchestrator.experimental.use_prefix_cache_salt flag — always salt inference requests with str(ckpt_step), for both training rollouts and evals.
• Drop the inference.experimental.reset_prefix_cache_after_update flag — the /update_weights and /load_lora_adapter endpoints no longer reset the prefix cache. The salt alone is sufficient to invalidate stale KV states across policy updates, making the reset path redundant.
• Remove the now-empty OrchestratorExperimentalConfig and InferenceExperimentalConfig classes and their parent experimental fields.
• Tighten cache_salt typing in envs.py from str | None to str (always set).

🤖 Generated with Claude Code

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Note

Medium Risk
Changes inference cache invalidation behavior by removing prefix-cache resets on weight/LoRA updates and making cache_salt mandatory and always derived from ckpt_step, which could affect serving performance/correctness if assumptions about vLLM cache salting are wrong.

Overview
Removes the configurable prefix-cache invalidation toggles (orchestrator.experimental.use_prefix_cache_salt and inference.experimental.reset_prefix_cache_after_update) and their associated wiring.

The orchestrator/scheduler now always injects cache_salt=str(ckpt_step) for training rollouts and evals (and cache_salt is now a required str throughout env APIs). Inference /update_weights and /load_lora_adapter no longer reset the vLLM prefix cache after applying updates.

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[cursor]

Empty experimental config classes left as dead code

Low Severity

After removing their only fields, OrchestratorExperimentalConfig and InferenceExperimentalConfig are now empty classes with no fields. They are still instantiated as experimental fields on OrchestratorConfig and InferenceConfig, but nothing in the codebase accesses .experimental anymore. The PR description explicitly states the intent to remove these classes and their parent fields, but this wasn't carried out.

Additional Locations (1)

• src/prime_rl/configs/inference.py#L246-L249

 

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