BFM-decomp/cookbook/C0202.md

§181 — WHAT A WAVE'S GATE ACTUALLY REJECTS (P31 S53, measured on wave R's 45-draft main pile)

Only ONE of 27 blocked drafts was wrong. The other 26 were correct and unbankable.

Wave R drafted 92/110 MATCH and its main pile carried 45 byte-verified drafts. 18 banked in the first slate. Every rejection was catalogued; five distinct classes, four of which match_one, reloc_identity, fragment_check and pregate_check are ALL structurally blind to:

class	n	how it announces itself	who could have caught it
MIRROR-FRAGMENT	2	undefined reference to '.L80050D5C' at LINK	nothing we had
duplicate typedef, TU's copy BELOW	7	C89 duplicate-typedef at COMPILE	pregate_check did
draft-vs-draft data-symbol type clash	1	previous declaration of D_80072784	nothing we had
draft-vs-file signature conflict	4	previous declaration of func_80032A74	nothing we had
genuinely byte-wrong	1	whole-binary SHA differs	only the build

1. THE MIRROR FRAGMENT — the reverse of §176i, and a new refusal we do not yet compute. fragment_check asks "does another symbol live INSIDE my range?". The opposite is equally fatal: another stub's .s branches into a label inside YOUR range, and converting you to C deletes that label. Two instances, both silent until the linker spoke:

• gfx2D_BG0_OBJ_4D8 — gfx2D_BG0_OBJ_1B4.s branches to .L80050D5C / .L80050D70 inside it;
• SYS_OBJ_26EC — SYS_OBJ_25C8.s branches to .L8005B9B8 inside it. The test is as cheap as the forward one: for each still-stubbed sibling .s, collect the .L targets it references and refuse any draft whose [addr, addr+4*nins) contains one. Shipped as fragment_check.branched_into(), negative-controlled on both known-bad drafts (it names them and the exact referring sibling) — and then measured across the corpus, which is the number that matters:

binary	stubs owning a branched-into label
main	99 of 1,745 (5.7%) — incl. SaveLoadRoutine, GsSortFastBg, the gfx2D_BG0_* cluster
ov_SC04_011	0 of 229
ov_SC03_028	0 of 194

So it is a main-specific hazard at ~1 in 18, and effectively absent from the overlay fleet. That asymmetry is itself informative: main is where splat's symbol table names the most non-function addresses. Two notes on the semantics — the check excludes labels a function defines itself, and it excludes siblings that are IN THE SAME SLATE (converting both at once removes the referencing .s, so the hazard evaporates). A population scan that puts every stub in one slate therefore correctly reports zero, which is a right answer to a different question.

2. THE TYPEDEF-BELOW CASE. gate_main.strip_dup_typedefs reuses a definition only when it is visible ABOVE the insertion point — correct, since stripping a below-survivor leaves the name undefined (that trap is documented in its own docstring). But it then KEEPS the draft's copy, and two definitions of one typedef name is a C89 error wherever they sit. Both horns are wrong; the missing third option is to rename the draft's private copy, or hoist the file's definition (typedefs emit no code, so hoisting is byte-neutral). 7 correct drafts are parked on this.

3. THE BISECT ECONOMICS ARE SETTLED. bisect_slate.py — null control first, then true binary search — isolated the single byte-wrong draft (SYS_OBJ_1DC0) in 5 steps / 90 seconds, at ~13 s per incremental build. gate_main's built-in bisect on a comparable slate ran 3 hours and named nothing (§176i). Never use the built-in one; always pass --no-bisect and drive bisect_slate.

4. THE STRATEGIC READING. 26 of 27 blocked drafts are byte-correct work that only the plumbing rejects, which is the §180b ratio again from a third independent direction. The lesson is not "draft better" — the drafting is done. It is that every hour spent making the integration layer compute a refusal is worth more than an hour of drafting, because drafting is already at 84–93%.