Drew T
2.6 KiB
§107 — A lever wired into ONE gate path is a lever most families cannot reach (Phase 29 T56, func_80144090 0/136 → 136/136)
The §103 tu-scope lever was wired into jtbl_family_bank (T53) and nowhere else. But that tool only
runs for has_mid_jr families; every other family sweeps through family_sweep, which gates via
plain harvest_verify by design. So the lever was unreachable from the path most families use, and
the symptom was indistinguishable from a compiler wall: func_80144090 swept 0/136 with
conflicting types for D_800A651C.
Wired into family_sweep's staging, the same family banked 136/136, 0 failed — +20,944
instructions — with no change to the drafts at all.
Why this does not violate the sweep's plain-harvest_verify rule. That rule exists because
gate_stage's transforms perturb a correct draft (the §19/T3 finding). The tu-scope never touches
the draft — it moves a declaration in the target TU. Different object, different risk. The test
for "may this run inside the sweep?" is not "is it a transform" but "does it change the draft?"
Reuse the existing undo, do not invent one. family_sweep already snapshots TUs it edits at
staging time (--normalize-self-decls) and reverts them on two conditions: a final MISMATCH (the edit
was not byte-neutral) and a zero-bank group (§61's undo law — an edit that bought nothing gets
undone, or a git add -A commits dead diff). The tu-scope shares that dict, so it inherits both
backstops for free. A staging-time TU edit without those two reverts is how a sweep leaves residue.
Default ON, with an opt-out. It is byte-neutral by construction, a no-op when nothing collides,
and auto-reverted when it buys nothing — so gating it behind a flag only means most runs silently
miss it (the T24 --allow-pins precedent). --no-tu-scope exists to A/B it.
The law: when a lever fixes a class, ask which gate paths can reach it before declaring the class handled. A class is only handled on the paths that can apply the fix — and the paths that cannot will keep reporting it as a wall, in language identical to a real one.
Related, from the same task: scope_tu_externs refused N>1 file-scope decls of a symbol as
"ambiguous". Duplicate-identical externs are legal C, so N identical decls are one declaration
written N times — delete all N. Now it compares whitespace-collapsed forms and refuses only on a
genuine disagreement. (Measured on D_800B9A02: 3 decls in 2 different forms — so that one was
correctly refused, and the relaxation did not paper over a real conflict.)