Self's review found that commit 4e6495dd's fix for F1 replaced the per-lane
forward-arithmetic defect with a second, still-independent membership
computation: Lane's own half-open admission (Lo <= s < Hi, from a cell's own
Extent) versus Lanes' ceil((cell.Lo - centreLateral) / laneSpacing) lane
index. The two agree only when a cell's own (Hi - Lo) equals the externally
supplied laneSpacing exactly in float -- the identical two-derivations trap
Cut 12.2's own fix batch already found and removed from Lane itself,
reintroduced one layer up. Confirmed reachable: on commit 4e6495dd, solid5
b=(0,1) s=0.49999997 n=1 leaves the ceil-based centre lane EMPTY while Lane(s)
itself finds all 5 cells of the row -- breaking R3 ("the centre lane always
meets metal", Commit's own guard) and the 12.2 placement contract.
FireControl.Lanes is now built entirely out of FireControl.Lane: it calls
Lane(hull, b, centreLateral + k * laneSpacing, ...) once per lane index, so
Lane(s) is literally this function's n = 0 case rather than a parallel
re-implementation of its rule. Commit's placement and Apply's damage split
now read one function. The narrower question left -- can two individually
correct Lane() calls, at two different lines, still walk the same cell? --
is resolved by ownership (the lane closest to the centre keeps a contested
cell; the centre lane, k = 0, never loses one), not by a competing formula,
so the centre lane's final cell set is always exactly Lane(centreLateral)'s
own output.
Lane() itself is unchanged (still called directly by Commit and by
FireControlCut12Tests' edge-seed and interval-edge tests, all still green:
HitsLandOnTheFacingEdge, LaneSeamIsHalfOpen, LaneNeverEmptiesAtAnIntervalEdge,
Cut12-edge-68442709, Cut12-edge-64078070).
Adds LanesQueryIsDisjointMatchesLaneAtCentreAndNeverEmptyOnHull: now that
Lanes is a public, pure geometric query, the boundary sweep is a behavioural
test of its own contract, no reflection -- over every cell's own shadow edge
and float neighbours, at exact-axis, 45-degree, |bx| > |by| bearings and
Soul's own two reproduction cases, spread 1-2: (a) no cell is walked by two
lanes, (b) the centre lane equals a plain Lane(s) call, (c) the centre lane
is never empty when the centre lateral is inside the hull's own shadow. Hand-
confirmed to fail on 4e6495dd's ceil-based Lanes (property (b), the same
input above) and to pass on this commit (fc123fix2-mut3.log).
Adds CommittedCellIsTheFirstCellTheCentreLaneDamages: an end-to-end check
through Fire -> Commit -> Apply (damageSpread 0, a single lane) that the
committed outcome.Cell is the first cell Apply damages.
Full suite: 286 tests, identical across 3 runs.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
cb71a3cfad