A rail reveal enters with an 8px nudge, not a slide from its own edge

Sub-issue of #13158 (dock layouts). The second of the dock-polish leaves the demo plan named (L2 — reveal motion); siblings: #18070 (L3, the reveal's geometry on a padded host), #18071 (L4, header-action tooltips).

Context

Clicking a rail tab reveals the auto-hidden pane as an overlay next to the strip. Today the overlay appears: it fades from 40% opacity and moves 8px, over the shared dock duration. The operator's design read (2026-09-02, the demo rehearsal): a reveal should slide in from the edge that owns it — a right rail slides right-to-left while the overlay's opacity rises, in the order of 300ms — so the eye reads where the pane came from and where it will go back to.

The Problem

The motion exists but is a nudge, not a slide. Measured on dev@5ae9358063:

• resources/scss/src/dashboard/Container.scss:150-170 — .neo-dashboard-dock-reveal-overlay { animation: neo-dock-reveal-fade var(--dock-transition-duration) var(--dock-transition-easing) } with the per-edge names the rail stamps (-left/-right/-top/-bottom); the keyframes start at opacity: 0.4 and translateX(±8px) / translateY(±8px).
• Container.scss:14/20 — --dock-transition-duration: var(--motion-panel, 280ms), --dock-transition-duration-fast: var(--motion-fast, 120ms); :136-140 collapses both to 0ms under prefers-reduced-motion: reduce (the token layer owns reduced motion, per #14779).
• src/dashboard/dock/interaction/RevealOverlay.mjs:192-214 — the overlay listens to its own animationend, holding one MotionSignal.enter/leave entry while the reveal animates (revealMotionActive); teardown settles the producer without an end event (:234).
• The hidden state is display: none (Container.scss:472-474): there is no exit motion, and none is asked for here.

An 8px travel from 40% opacity over 280ms reads as a flicker at pane scale (the overlay is 12rem+ wide); the pane's origin is not legible.

The Architectural Reality

• #14779 established the dock motion contract: durations come from ONE token set (--dock-transition-*), never literals at call sites; motion is observable (dock-animating / animationend-driven completion); reduced motion collapses at the token layer. The reveal already rides that contract through the overlay's animationend → MotionSignal pair — a longer or different keyframe keeps it as long as the animation still ends on the overlay element.
• The per-edge cls (neo-dashboard-dock-reveal-overlay-<edge>) is stamped by the rail (RevealOverlay.mjs:291-294), so the direction is already known to CSS; the change is confined to keyframes and one token.
• ADR 0029 §2.6 (auto-hide interaction layer, #13280): the reveal is runtime-only geometry; motion does not touch the document.
• Not this leaf: where the overlay starts (touching the strip vs. covering it) is #18070's geometry; a reveal inside an iframe pane is #18067.

The Fix

resources/scss/src/dashboard/Container.scss:

1. One new token in the existing set: --dock-transition-duration-reveal: var(--motion-reveal, 300ms), collapsed to 0ms in the reduced-motion block beside its siblings.
2. The overlay's animation reads that token (easing stays --dock-transition-easing, the soft ease-out).
3. The four per-edge keyframes start fully outside the overlay's own box and transparent: from { opacity: 0; transform: translateX(100%) } for -right (-100% for -left, translateY(±100%) for -bottom / -top); the edge-less fallback keeps a fade from 0.
4. overflow on the reveal's host must clip the travel so the overlay never paints over the strip mid-flight — read the host rule before adding one; if the rail host already clips, no change.

No JavaScript changes are expected; if MotionSignal needs the animation name (it should not — it listens to animationend on the overlay), that is a finding to record, not to work around.

Contract Ledger Matrix

Decision Record impact: aligned-with ADR 0029 (§2.6 runtime-only reveal); amends nothing.

Acceptance Criteria

• After a rail-tab click in a real browser, the overlay's computed animation-name is the owning edge's keyframe and animation-duration is 0.3s; sampled within the first frame its transform carries the edge-ward offset, settled it is the identity — a component spec under test/playwright/component/dashboard/ on an existing dock-rail fixture, one arm per horizontal edge at least, red on dev (today's transform at t≈0 is ≤ 8px).
• With reducedMotion: 'reduce' emulated, the same read is 0s (the token layer collapses it; no per-site check).
• The overlay still settles: MotionSignal leaves after the animation and the existing rail / overlay unit specs stay green (test/playwright/unit/dashboard/).
• Visual read on the FM cockpit and on apps/workstation (right rail and left rail), both themes: the pane slides in from its strip and never paints over the strip mid-flight; screenshots in the PR, design-read.
• No duration literal at the call site (review-checkable, #14779 AC).

Out of Scope

• Exit motion (the hidden state is display: none; a two-phase hide is its own leaf if wanted).
• The overlay's start geometry on padded hosts (#18070), iframe dismissal (#18067), header-action tooltips (#18071).
• Pin / restore transitions (FLIP layer, #14929).

Related

Parent: #13158. Motion contract: #14779; FLIP layer: #14929; auto-hide interaction layer: #13280 / ADR 0029 §2.6. Siblings: #18070, #18067, #18071. Consumer read: neomjs/neo-agent-institution (FM cockpit) and apps/workstation.

Live latest-open sweep: checked the latest 20 open issues at 2026-09-02T11:38Z (none on reveal motion; #18070 is geometry, #18067 dismissal, #18027 the maximize FLIP flash); A2A claims of the last hour: L3 (Ada), L4 (Mnemosyne), #18067 (Vega) — none on motion; ask_knowledge_base (ticket) surfaced #14779 / #13280 as the contract, no equivalent leaf; the local ticket corpus has no reveal-motion ticket.

Origin Session ID: 91f83b9c-df95-4f72-a68f-d33f470792ac

Retrieval Hint: "dock reveal overlay slide from edge keyframes --dock-transition-duration-reveal MotionSignal"

📜 Clio