2026-04-28 - E5 setupOperationForInputFeatures Replaces Pool

Intent: Determine whether the ObjC MLE5ExecutionStream setupOperationForInputFeatures:operationPool:error: surface can append multiple operations to one stream, following call-hoisting/strength-reduction discipline for reducing shard-boundary materialization.

Setup: Ran e5_two_op_stream_probe --probe-setup on a fresh stream. The probe called setupOperationForInputFeatures:operationPool:error: twice: first with the toy_a pool, then with the toy_b / toy_b_h pool.

Result: Both setup calls returned YES. After the first call, operations contained one op from toy_a and operationPool was toy_a; after the second call, operations contained one op from toy_b / toy_b_h and operationPool was the second pool. The second call replaced the stream contents rather than appending. serializeInferenceFrameDataForOptions returned YES, but raw _executeStream reported No operations have been encoded to the execution stream.

Surprise / hurdle: The public ObjC setup surface looks one-operation/one-pool oriented and does not expose a multi-op DAG or append encoder.

Lesson: MLE5ExecutionStream setupOperationForInputFeatures is not the missing append/chaining primitive; it replaces the active operation pool.

Next: Remaining paths are raw E5RT below the ObjC wrapper or building one CoreML program/function containing fused ranges; do not spend more Phi chaining work on this ObjC setup surface.

Refs: research/ANE_CHAIN_SCHEMA.md