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The drag learns the stepper's trick — past the screen's edge, lane growth re-divides instead of stopping

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The right-edge drag's growth was capped at the screen's visible frame,
because each snap tick grows the window; on a window near the screen edge
that left a lane stuck at a tick or two of headroom. Settled 2026-08-08
(03-board-ui.md § Lane, superseding the pathfinder's hard stop): at the
screen the window pins and each further tick re-divides the fixed strip
width across one more unit — siblings compress, the stepper's mechanism
arriving under the drag's fingers. The regimes meet with no pixel jump
(the re-divided standard at the fit IS the frozen standard, by the
exact-fill identity), shrinking mirrors the way back, the rubber band
moves to the strip's own capacity, and a window with no headroom at all —
full screen included — re-divides from the very first snap.

New pure arithmetic in LaneLayoutMath (pinnedStripWidth, resizeStandard,
resizeMaxUnits, resizeWindowDelta, snappedUnits over per-count slots);
LaneResizeSession splits the tick across the regimes and derives its
standard from the live count; the handle and BoardView hand the session
the strip's whole divide. 2709 unit tests green (+11).

Claude-Session: https://claude.ai/code/session_014PtZdPwqZuqEDLc6wZMtEy
This commit is contained in:
rzen
2026-08-08 21:36:56 -04:00
parent 05b1a787de
commit 9a52b795b2
8 changed files with 564 additions and 91 deletions
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KanbanTests/LaneLayoutMathTests.swift
+187 -15
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@@ -15,9 +15,12 @@ import Testing
/// back to `k - 1` is `slotWidth(k - 1) + gap - reentry`, 10pt shy of that same boundary — so 2↔1
/// ticks down at 102 (112 − 10) and 3↔2 at 214 (224 − 10).
///
/// Where the pathfinder's twin suite pinned a hard 1…3 width cap, these pin the *screen fit*: in
/// Lanework `allowedRange`'s ceiling is only ever how far the window can grow (`maxUnits`), because
/// the width field itself has no cap.
/// Where the pathfinder's twin suite pinned a hard 1…3 width cap, these pin the two regimes the
/// screen fit divides (03-board-ui.md § Lane, settled 2026-08-08): up to the fit a tick grows the
/// window, past it a tick re-divides the pinned strip, and `allowedRange`'s ceiling is the strip's
/// own capacity rather than either — the width field itself has no cap. The suites below take a
/// screen fit as a *range* where the mechanism is not what is under test, and the re-divide gets its
/// own suite at the foot of the file.
private let standard: CGFloat = 100
private let gap: CGFloat = 12
@@ -311,26 +314,26 @@ struct LaneSnapTests {
@Test("The snap never steps past the allowed range")
func neverTicksPastTheAllowedRange() {
#expect(snapped(5000, current: 3) == 3, "the on-screen fit is the ceiling")
#expect(snapped(5000, current: 3) == 3, "the range's ceiling holds")
#expect(snapped(0, current: 1) == 1, "one unit is the floor")
#expect(snapped(-500, current: 1) == 1)
}
@Test("The ceiling is the screen fit, and it is the only ceiling")
func snapRespectsTheOnScreenFit() {
// With the fit capping the range at 2×, no live width ticks to 3×.
let fitsTwo = 1...2
#expect(snapped(1000, current: 2, range: fitsTwo) == 2)
#expect(snapped(5000, current: 2, range: fitsTwo) == 2)
@Test("The range's ceiling is the only ceiling, and it is not a width cap")
func snapRespectsTheAllowedCeiling() {
// With the range capped at 2×, no live width ticks to 3×.
let capsAtTwo = 1...2
#expect(snapped(1000, current: 2, range: capsAtTwo) == 2)
#expect(snapped(5000, current: 2, range: capsAtTwo) == 2)
// Below the cap it still ticks normally.
#expect(snapped(200, current: 1, range: fitsTwo) == 2)
// A roomier screen keeps ticking well past the pathfinder's old 3× ceiling — Lanework's
// width has no cap of its own (03-board-ui.md § Lane).
#expect(snapped(200, current: 1, range: capsAtTwo) == 2)
// A roomier ceiling keeps ticking well past the pathfinder's old 3× — Lanework's width has
// no cap of its own (03-board-ui.md § Lane).
#expect(snapped(5000, current: 3, range: 1...9) == 4)
#expect(snapped(5000, current: 8, range: 1...9) == 9)
}
// MARK: maxUnits
// MARK: maxUnits — the boundary, not the ceiling
@Test("maxUnits turns window headroom into whole growable units")
func maxUnitsFromHeadroom() {
@@ -338,7 +341,8 @@ struct LaneSnapTests {
#expect(LaneLayoutMath.maxUnits(currentUnits: 1, headroom: 250, step: step) == 3)
// Just over one step → +1.
#expect(LaneLayoutMath.maxUnits(currentUnits: 1, headroom: 120, step: step) == 2)
// Less than a step → no growth room, but shrinking stays allowed.
// Less than a step → no window growth left, so the drag re-divides from its very first
// tick; shrinking stays allowed either way.
#expect(LaneLayoutMath.maxUnits(currentUnits: 1, headroom: 50, step: step) == 1)
#expect(LaneLayoutMath.maxUnits(currentUnits: 2, headroom: 0, step: step) == 2)
// Never below currentUnits even with a negative headroom (a window already past the visible
@@ -373,3 +377,171 @@ struct LaneSnapTests {
maxSlot: slot(3), resistance: 0.25) == 343)
}
}
// MARK: - The drag past the screen
/// The right-edge drag's **second regime** (03-board-ui.md § Lane, settled 2026-08-08): at the
/// screen's visible frame the window stops growing, and each further tick re-divides the now-pinned
/// strip across one more unit instead — the stepper's mechanism, driven by the drag, with the
/// siblings compressing. Before this the tick simply clamped at the fit, so a lane on a maximised
/// window refused to widen at all.
///
/// Fixture: the file's standard of 100 and gap of 12 on a **four-unit strip** — the dragged 1× lane,
/// two more 1× lanes and the shown trash's fixed unit — with two whole steps of screen headroom, so
/// the fit is 3×. The strip is 100·4 + 12·5 = 460 at drag start and 460 + 2·112 = 684 once the window
/// is flush against the screen, which is the width every tick past 3× re-divides.
@Suite("LaneLayoutMath ▸ the drag past the screen")
struct LaneRedivideTests {
private let startUnits = 1
private let startTotal = 4
private let fit = 3
private let pinned: CGFloat = 684
private func standardFor(_ units: Int) -> CGFloat {
LaneLayoutMath.resizeStandard(
forUnits: units, startUnits: startUnits, startStandard: standard,
startTotalUnits: startTotal, fittingUnits: fit, gap: gap)
}
private func slotFor(_ units: Int) -> CGFloat {
LaneLayoutMath.slotWidth(units: units, standard: standardFor(units), gap: gap)
}
private var ceiling: Int {
LaneLayoutMath.resizeMaxUnits(
startUnits: startUnits, startStandard: standard,
startTotalUnits: startTotal, fittingUnits: fit, gap: gap)
}
private func snapped(_ liveWidth: CGFloat, current: Int) -> Int {
LaneLayoutMath.snappedUnits(liveWidth: liveWidth, currentUnits: current,
slotFor: slotFor, gap: gap,
allowedRange: 1...ceiling, reentry: reentry)
}
// MARK: The pinned strip
@Test("The pinned strip is the drag-start strip plus one step per unit of screen headroom")
func pinnedStripWidthIsDerivedNotMeasured() {
#expect(LaneLayoutMath.pinnedStripWidth(
startUnits: startUnits, startStandard: standard,
startTotalUnits: startTotal, fittingUnits: fit, gap: gap) == pinned)
// No headroom at all: the strip is exactly what the frozen standard and the unit total
// imply, and the re-divide starts from the very first tick.
#expect(LaneLayoutMath.pinnedStripWidth(
startUnits: startUnits, startStandard: standard,
startTotalUnits: startTotal, fittingUnits: startUnits, gap: gap) == 460)
}
// MARK: Continuity at the boundary
@Test("The two regimes meet with no pixel jump")
func theBoundaryCostsNothing() {
// Everything up to the fit is the frozen standard: the window took the step, so the
// division never moved.
#expect(standardFor(1) == standard)
#expect(standardFor(2) == standard)
#expect(standardFor(fit) == standard, "the re-divided standard AT the fit is the frozen one")
// Past it the same width divides across one more unit, so it can only shrink.
#expect(standardFor(fit + 1) < standard)
#expect(abs(standardFor(fit + 1) - 84) < 0.0001) // (684 − 12·8) / 7
#expect(standardFor(fit + 2) < standardFor(fit + 1))
}
@Test("Past the fit the strip still fills exactly — the width is pinned, the division is not")
func exactFillSurvivesTheRedivide() {
for units in (fit + 1)...12 {
let redivided = standardFor(units)
// Four boxes stand in the strip — the dragged lane, two 1× lanes and the trash — so
// there are five gaps: the three between them and the two outer margins.
let filled = slotFor(units) + 3 * redivided + 5 * gap
#expect(abs(filled - pinned) < 0.0001, "\(units)× must still fill the pinned strip exactly")
}
}
// MARK: The snap, measured slot by slot
@Test("A tick past the fit fires on the re-divided slot, and does not double-tick")
func theRedivideTicksOnceAndSettles() {
// 3× is the last slot the window pays for: 324 wide, its trailing gap ending at 336.
let threshold = slotFor(fit) + gap
#expect(threshold == 336)
#expect(snapped(threshold, current: fit) == fit, "exactly at the far edge holds (strict >)")
let ticked = snapped(threshold + 0.1, current: fit)
#expect(ticked == fit + 1, "the old clamp at the screen fit is gone")
// 4× is measured against the SMALLER standard the re-divide produced, and its threshold
// still sits beyond the width that fired the tick — so the session's iteration settles in
// one step rather than running away up the strip.
#expect(slotFor(fit + 1) + gap > threshold + 0.1)
#expect(snapped(threshold + 0.1, current: ticked) == ticked, "no double tick")
// And it does not immediately reverse either: the tick-down threshold is 10pt back inside
// the gap it just cleared.
#expect(snapped(threshold + 0.1, current: ticked) != fit)
}
@Test("Ticking back down retreats through the same re-divided slots")
func theRedivideTicksBackDown() {
// Coming back from 4×, the boundary is slot(3) + gap = 336 and the re-entry point 10pt
// inside it, at 326 — the same asymmetry as within the fit.
#expect(snapped(326, current: fit + 1) == fit + 1)
#expect(snapped(325.9, current: fit + 1) == fit)
#expect(snapped(330, current: fit + 1) == fit + 1, "re-entering the gap is not enough")
}
@Test("The ceiling is the strip's capacity, and units run well past the screen fit")
func theCeilingIsTheStripsCapacity() {
// 684 wide with 12pt gaps divides into at most 51 whole units before `standardWidth`'s 1pt
// floor would break the exact fill — floor((684 − 12) / 13) — and the dragged lane reads
// that back through the 47 units it added.
#expect(ceiling == 48)
#expect(ceiling >= fit)
#expect(standardFor(ceiling) >= 1)
#expect(abs(slotFor(ceiling) + 3 * standardFor(ceiling) + 5 * gap - pinned) < 0.0001)
// One unit further the 1pt floor engages, the division stops being a division, and the
// strip would overflow — which is precisely why the ceiling sits where it does.
#expect(standardFor(ceiling + 1) == 1)
#expect(slotFor(ceiling + 1) + 3 + 5 * gap > pinned)
// The snap walks all the way there and stops.
#expect(snapped(5000, current: fit) == fit + 1)
#expect(snapped(5000, current: ceiling) == ceiling)
}
@Test("The ceiling never falls below the screen fit, and a degenerate strip falls back to it")
func theCeilingFallsBackToTheFit() {
// Shrinking is always allowed, so the fit is the floor of the ceiling however odd the
// inputs are — a non-finite standard and a gap that would make the capacity formula
// meaningless both answer the fit rather than inventing a bound.
let degenerate: [(CGFloat, CGFloat)] = [(.nan, gap), (.infinity, gap), (standard, -1), (standard, -50)]
for (brokenStandard, brokenGap) in degenerate {
#expect(LaneLayoutMath.resizeMaxUnits(
startUnits: startUnits, startStandard: brokenStandard,
startTotalUnits: startTotal, fittingUnits: fit, gap: brokenGap) == fit)
}
// A start already past the fit (a window hanging off the screen) still cannot be clamped
// below where it stands.
#expect(LaneLayoutMath.resizeMaxUnits(
startUnits: 6, startStandard: .nan,
startTotalUnits: startTotal, fittingUnits: fit, gap: gap) == 6)
}
// MARK: The window's share of a tick
@Test("The window moves only for the part of a step that fits on screen")
func theWindowTakesOnlyItsShare() {
// Wholly inside the fit: every unit is the window's.
#expect(LaneLayoutMath.resizeWindowDelta(from: 1, to: 3, fittingUnits: fit, step: step) == 2 * step)
// A flick across the boundary: only the first unit was ever the window's to give.
#expect(LaneLayoutMath.resizeWindowDelta(from: 2, to: 5, fittingUnits: fit, step: step) == step)
// Wholly above it: the window is pinned and the re-divide does the whole of the work.
#expect(LaneLayoutMath.resizeWindowDelta(from: 4, to: 7, fittingUnits: fit, step: step) == 0)
#expect(LaneLayoutMath.resizeWindowDelta(from: fit, to: fit + 1, fittingUnits: fit, step: step) == 0)
// Shrinking mirrors it exactly — the step handed back is the one that was taken.
#expect(LaneLayoutMath.resizeWindowDelta(from: 5, to: 2, fittingUnits: fit, step: step) == -step)
#expect(LaneLayoutMath.resizeWindowDelta(from: 7, to: 4, fittingUnits: fit, step: step) == 0)
#expect(LaneLayoutMath.resizeWindowDelta(from: 3, to: 1, fittingUnits: fit, step: step) == -2 * step)
#expect(LaneLayoutMath.resizeWindowDelta(from: 4, to: 4, fittingUnits: fit, step: step) == 0)
}
}