Batch in-seq CP rerange has two lengths under compute padding: source payload length includes synthetic rows used only to keep CP compute well-shaped, while output length must expose only valid request rows. The torch fallback now computes rank-major source offsets from compute splits and output placement from valid splits.
Constraint: Tiny extend batching can add compute-padding rows that must not appear in restored valid token order.
Rejected: Use valid splits for source offsets | following requests on the same rank are shifted when a previous request has padded mirror rows.
Confidence: medium
Scope-risk: narrow
Directive: Batch rerange implementations must distinguish source compute splits from valid output splits.
Tested: python -m py_compile on changed runtime files.
Not-tested: Local pytest blocked before collection by missing orjson dependency.
(cherry picked from commit 31e741477503caa52f3a23acdc1286f46079043c)
0f9b445131