Phase 5 — Execute (Iteration 3)

What was built

iteration-3/pathfinding-race.html — the iteration-2 artifact restyled into a light, Apple-style design. Appearance only; no JS, structure, control, mode, or algorithm change. v2 left intact as a record.

Changes, all concentrated in <style> plus two tiny markup touches:

Palette: rewrote :root to the validated light tokens — page #f5f5f7, white cards, ink #1d1d1f, secondary #6e6e73, accent #0071e3; cell states re-derived for white (start green, goal red, ink walls, orange mud, cyan frontier, light-gray visited, #ffd60a path + inset ring).
Surfaces/depth: removed the graph-paper repeating-linear-gradient body, radial glow, all gradients and neon glows; cards now use large radius (18px) + soft diffuse shadow, hairlines only where needed.
Typography: large light heading (40px), system (SF) stack, secondary-gray body, generous spacing/line-height. Eyebrow recolored to accent.
Controls: paint tools wrapped in an Apple-style segmented control (.segmented, button IDs preserved); pill buttons; primary Play = filled blue pill; active toggle/thumbs = blue; custom range thumb. Study toggle emoji → clean "Study Mode" text.
Identity: four algorithm hues reduced to small dots via .pname::before and thumbnail dots.
Study view: light pseudocode card, accent active-line, accent-tinted narration in dark blue, blue node cursor + red neighbor cursor, accent focus-row in the table.

Two markup touches (only non-CSS edits)

Wrapped the three existing paint buttons in <span class="segmented"> — IDs unchanged.
Replaced the 📖 toggle label with text "Study Mode".

No JavaScript was modified.

Tests (all green) — saved under `iteration-3/tests/`

Suite	Scope	Result
`i3_v2_verify.js`	inlined engine re-test + static security	42/42 + 8/8
`i3_v2_integration.js`	race behaviour unchanged	20/20
`i3_v2_study.js`	study behaviour unchanged	26/26
`i3_v2_verify_extra.js`	panel-click, blurb, cursors	9/9
`i3_style.js`	new style shipped + dark removed + IDs preserved	31/31
`contrast.js`	palette contrast (shipped values)	all pass

97 behaviour assertions + 8 static + 31 style + contrast — all pass. The full v2 regression suite passed unchanged against the restyled file, confirming the redesign is behaviour-neutral.

Issue found and resolved

path vs closed luminance (1.11:1). Brightening the path to #ffd60a (to separate it from the cyan frontier, per Research) brought it close in luminance to the light-gray closed state. This is the documented three-way squeeze. Resolved by design, not by recolour: the final path carries a non-colour inset ring (box-shadow:inset 0 0 0 2px #d4a800), so it's never distinguished by fill alone (WCAG 1.4.1). The shipped ring is asserted in i3_style.js; contrast.js was updated to document this relationship honestly rather than flag a false fail.
No behavioural bugs — the regression suite stayed green at every step.

Acceptance criteria results (vs. plan checklist)

#	Criterion	Result
1	All 24 prior criteria pass (full v2 suite green)	PASS — 97/97 behaviour + 8 static
2	Light palette; no graph-paper/glow/gradient	PASS — style asserts old colors + texture removed
3	Single blue accent on interactive elements	PASS — tokens + style checks
4	Algorithm identity as small dots; chrome neutral	PASS — `.pname::before` + thumb dots
5	Cards: large radius + soft shadow, not borders	PASS — `box-shadow:var(--shadow)` asserted
6	SF type, larger/lighter heading, generous spacing	PASS — 40px heading, system stack
7	Segmented paint control; blue-pill Play	PASS — `.segmented` + wrap asserted
8	Cell states light palette; path non-colour cue	PASS — ring asserted
9	Study view cohesive in new style	Styled; visual cohesion → Verify (human)
10	Contrast passes	PASS — text AA; states distinguishable (path via ring)
11	Offline; no innerHTML/eval/fetch/URLs/web fonts	PASS — 8/8 static; system fonts only
12	No test-breaking id/class renames	PASS — all IDs asserted present; suite green

Honest handoff to Verify

Functional behaviour is fully green (regression unchanged). What automation can't judge — whether the redesign actually looks light, clean, and elegant; visual cohesion of race + study views; how the segmented control, shadows, and palette read on screen — is the deliverable's real point and needs a human look in Verify.