sglang/.claude/rules/forward-batch-init-new-purity.md

paths

paths
**/*.py

ForwardBatch.init_new must not mutate the ScheduleBatch

init_new (and any ForwardBatch factory) treats the input ScheduleBatch as read-only. Per-forward overrides go through the kw-only params of init_new / TpModelWorker.forward_batch_generation, never a ScheduleBatch field. Batch-prep writes (out_cache_loc, seq_lens_*, ...) before init_new are out of scope.

Tolerated exceptions (don't add new ones):

• seq_lens_sum backfill — the seq_lens family is slated for removal (→ kv-committed lengths).
• sampling_info sub-object writes (grammars, canary ids) — shared object, until the sampling forward-copy op.
• _expand_mrope_from_input memoizing mrope_position_delta_repeated_cache — pre-existing.