Clean Core Copilot: IBM Bob reviews old SAP code

Problem. SAP ends mainstream maintenance for ECC 6.0 on 31 December 2027. Picture the one ABAP developer at a mid-size manufacturer with 600 custom programs and that deadline. Every company moving to S/4HANA Cloud carries hundreds of custom ABAP programs written over fifteen years. Each one must be checked against SAP's Clean Core rules and often rewritten before it can move. Today that review is manual, done by the few consultants who know both the old and the new world. It is slow, expensive and inconsistent, and nobody knows how far an AI assistant can be trusted with it. That is the question a project manager actually asks: not "can Bob do this?" but "how well, measured, and where does it fail?" Solution. Clean Core Copilot is an IBM Bob custom mode plus an evaluation harness. Before the hackathon we wrote four synthetic legacy programs (finance, sales, materials) with 41 planted problems, a twelve-rule Clean Core catalogue, and an answer key. The key stays outside the repository; its SHA-256 was committed on 24 September, before Bob saw any code, and the organisers confirmed the preparation. During the hackathon Bob, in the "Clean Core Architect" mode, audited all four programs and wrote JSON findings with a rule ID, line range and reason for each. We scored them against the sealed key and confirmed every judgement by hand. Results. Bob found 27 of 29 catalogue violations on the right lines and 1 of 12 business-logic defects. Of the 32 findings we could judge, 29 were correct (91 %): two were wrong and one partly right; six more were duplicates. Bob then rewrote one program into a CDS view, a class and seven ABAP Unit tests, and rewrote the other three in parallel with three sub-agents in sixteen minutes. On a real SAP BTP trial system the view failed on exactly the two SAP objects Bob had marked candidate; with two labelled stand-in tables the class compiled, Bob's seven tests passed and ATC reported zero errors. A differential test against the old rule on 431 cases passed too (8 of 8), and changing one limit from 30 to 31 days made two tests fail. Getting there exposed two syntax defects in Bob's code that only a compiler finds. What it means. Bob is a strong first reviewer for catalogue rules and a weak one for business logic. The human stays in the loop, and we can now say where, with numbers. A recorded-evidence site shows every finding next to the code, whether Bob was right, and what was and was not verified. Total cost: 4.26 of 40 Bobcoin. Limits. The samples are synthetic (customer ABAP cannot be published); the numbers describe this test, not Bob in general. One of four rewrites was tested, against stubs; three are unreviewed. Nothing was verified on a customer's system.