BFM-decomp/cookbook/C0178.md

§171a — THE MECHANICAL A-PROP DRAFT (P30 S50): 256 members banked with no agent in the loop

The claim. A lane-A member shares its family's h_seq with a MATCHED sibling, so its body IS that sibling's body with the per-location environment rebased. Two mechanisms had each taken a run at that population and each left it on the table:

• family_sweep --hseq remaps mechanically but CARRIES the seed's declaration layer, and its dominant failure is decl-agreement — 331 of the 458 verdicts in S49's post-repair ledger. The body was never the problem; the decls it dragged along were.
• the A-prop agent wave re-derives the same body at ~80k tokens per banked function — and got the per-location symbol wrong every time it mattered (§171).

tools/aprop_autodraft.py does neither: seed body + family_remap.symbol_map (positional reloc zip, three-oracle target spelling) + a minimal preamble synthesized from scratch — one extern per symbol the body actually references, plus only those seed typedefs the body names and the destination does not already define. Nothing else travels. 256 banked at zero agent tokens (222 + 34), against ~20M tokens the same work would have cost as a wave.

THE SELECTOR IS THE TOOL. Everything below was learned by launching at scale and stopping when the verdicts disagreed with the plan. Each fix moves a failure from build time to generation time, and at ~1 min per gate group that difference IS the run:

Refusal	Why a draft cannot work	Measured
classify_member != PURE	a rename reaches a RELOC site and nothing else	first 5 failures were 5/5 IMM or STRUCT
no definition after rename	the seed name was recovered by scanning the body for the first func_XXXX( — in a de-macroized block that is the first extern declaration, so a CALLEE got the member's name and the definition kept the seed's	48 caught; the symptom was undefined reference to <member>
arity conflict	the destination already declares a callee with named parameters the body underfills	17 on one symbol alone
undefined data	the draft references a symbol nothing in the DESTINATION binary defines — the seed's environment does not exist there	43 + 33 on two symbols
.s carries data or a jtbl	the data lives INSIDE the stub being replaced, or the carve path refuses	90 of 584

Macro seeds are the majority and they are a trap. 567 of 1,196 members sit behind a DEFINE_<fn>() engine_core macro (all 3,737 de-macroize cleanly). Pasting the de-macroized block whole reintroduces exactly the decl-agreement failure this design exists to avoid: measured inline 145/213 (68%) vs macro 77/276 (28%), with the macro failures reading parse error before '*' and too few arguments. func_8016AB6C's macro block is 1,891 lines of which 108 are the function. Take the DEFINITION; keep the block only as the decl source.

IMM is not a wall, it is a second engine. T2a's imm_map_tier1 resolves a per-location LITERAL exactly as symbol_map resolves a per-location SYMBOL: 131 of 275 IMM members resolve with zero unresolved sites. Only STRUCT (register/opcode drift, 238 members / 4,259 ins) genuinely needs a per-member edit.

Negative-control every refusal before you ship it (tools/draft_prechecks.py, run against ALL 205 banked drafts of the first run: zero false positives, catches 39 of 67 known failures). That control found two bugs in the checks themselves, both of which would have thrown away good work silently: C89 f() declares UNSPECIFIED parameters, not zero — so decl 0 vs call 1 is no conflict at all — and a member's own definition read as a call to itself. A pre-check that discards good drafts is worse than one that lets a few builds fail; when in doubt make it CONSERVATIVE (flag only decl > call, on named parameters).