feat(replay): add full-screen tableau dim layer for mini-tableau preview

Spawn a `ReplayTableauDimLayer` UI node (100% × 100%, 50% opacity black)
at z=54 (Z_REPLAY_OVERLAY − 1) whenever a replay starts. The dim layer
darkens the entire card world so the replay chrome (banner at z=55,
move-log panel at z=55) reads clearly against the scene without
obscuring card positions — matching the mockup's "Game Peek Band at
50% opacity" spec. Bevy's UI/world compositor means no changes to
card_plugin are needed: UI nodes always render above world-space sprites
regardless of Transform.z values.

The dim layer carries no Interaction component (purely visual; pointer
events pass through). Despawned alongside the banner and move-log panel
in `react_to_state_change` when the replay ends.

Adds Z_REPLAY_DIM (= 54) and TABLEAU_DIM_ALPHA (= 0.5) constants plus
two new tests: lifecycle (spawn/despawn mirrors floating chip pattern)
and z-ordering invariant (Z_REPLAY_DIM < Z_REPLAY_OVERLAY pinned).

1275 tests pass / 0 failing. Closes the last major B-2 sub-piece.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -6,9 +6,269 @@ project follows [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased]
 
-No threads in flight. v0.21.4 cut on 2026-05-08; CHANGELOG accumulates
+No threads in flight. v0.21.6 cut on 2026-05-08; CHANGELOG accumulates
 the next cycle here.
 
+## [0.21.6] — 2026-05-08
+
+Patch release for the post-v0.21.5 work. Through-line:
+**Move Log panel + scrub-UX polish**. v0.21.5 closed out the
+keyboard-accelerator surface (Space / Esc / ← / →) and the
+keybind footer; v0.21.6 builds on that with two parallel
+threads — accessibility + scrub-on-hold polish for the v0.21.5
+surfaces, plus a brand-new Move Log panel anchored to the
+viewport's bottom edge that gives players a 5-row recent-and-
+upcoming move history alongside the existing top-edge banner.
+
+The Move Log panel is the first replay-overlay surface that
+*isn't* attached to the banner — it lives at a separate screen
+anchor (bottom: 0) with its own spawn/despawn lifecycle.
+Establishes the pattern for "multi-anchor replay UI" that the
+remaining B-2 sub-piece (mini-tableau preview) will inherit.
+
+### Added
+
+- **HC-mode coverage for the scrub track + quarter-mark notch
+  ticks** (`d3cb1a5`). Adds parallel primitive
+  `HighContrastBackground` to `ui_theme` and a paint system
+  `update_high_contrast_backgrounds` in `settings_plugin` that
+  mirrors the existing border-marker pattern but targets
+  `BackgroundColor` instead of `BorderColor`. Tags the 1 px
+  scrub track Node and all five quarter-mark notch ticks so
+  they bump from `BORDER_SUBTLE` (`#505050`) →
+  `BORDER_SUBTLE_HC` (`#a0a0a0`) under HC mode. Scrub fill
+  (`ACCENT_PRIMARY`) and WIN MOVE marker (`STATE_SUCCESS`)
+  don't get the marker — accent and state colours are already
+  saturated and don't need an HC luminance variant.
+- **Continuous scrub on key-held arrow keys** (`2e25476`).
+  Holding ← or → triggers continuous step at 100 ms cadence
+  (10 steps/sec) — matches the mockup's `[← →] scrub`
+  terminology while keeping single-press = single-step
+  semantics. Per-key accumulators in a new
+  `ReplayScrubKeyHold` resource; `just_pressed` events bypass
+  the accumulator and fire immediately. Release resets to 0
+  so the next fresh press fires immediately rather than at
+  half-interval.
+- **Move Log panel** (`d6f32d3` + `140251b` + `e7345ae` +
+  `4437a1a`). New bottom-edge UI panel showing a 5-row window
+  onto recent + upcoming moves: 2 prev rows above the active
+  row + active row highlighted in `ACCENT_PRIMARY` + 2 next
+  rows below. Header reads `▌ MOVE LOG · N/M` (or
+  `▌ MOVE LOG · COMPLETE` when finished). Active row carries
+  a `▶` focus prefix and `TEXT_PRIMARY_HC` text colour for
+  legible contrast against the brick-red highlight. Prev /
+  next rows render in `TEXT_SECONDARY` so the active row
+  stays the focal point.
+  - Sibling-of-banner pattern (separate root entity anchored
+    at viewport bottom, not a banner child) — same
+    spawn/despawn lifecycle as `ReplayFloatingProgressChip`,
+    different screen anchor.
+  - Five pure helpers handle the formatting:
+    `format_pile`, `format_move_body`,
+    `format_move_log_header`, `format_kth_recent_row` (active
+    + prev), `format_kth_next_row` (next). 1-indexed display
+    numbers throughout (`Foundation(2)` reads as "foundation
+    3" rather than the enum's 0-index).
+  - Panel grows from 56 → 84 → 112 px across the four
+    move-log commits. `MOVE_LOG_PREV_ROWS` and
+    `MOVE_LOG_NEXT_ROWS` constants (both = 2) parameterise
+    the row count; `format_kth_recent_row` and
+    `format_kth_next_row` return empty for out-of-range k so
+    panels gracefully under-fill at the start (cursor=1) and
+    end (cursor=N-1) of a replay.
+  - HC marker on the panel's top border so the 1 px edge
+    bumps under HC mode (same pattern as the keybind footer).
+
+### Changed
+
+- **`react_to_state_change` despawns the Move Log panel** on
+  `Playing → Inactive` alongside the banner root and floating
+  progress chip. Third query in the same defer-and-despawn
+  cycle.
+- **Move Log panel height grew 56 → 84 → 112 px** across the
+  prev-rows and next-rows commits. The panel is sized to fit
+  the chosen row count + header + padding; tunable via the
+  `MOVE_LOG_PANEL_HEIGHT` const.
+- **`format_active_move_row` now prefixes the `▶` focus
+  marker** (`e7345ae`). Wraps `format_kth_recent_row(state, 1)`
+  and prepends the prefix when the body is non-empty. Empty
+  case still returns empty — cursor=0 doesn't paint a stray
+  `▶` on an otherwise-empty row.
+
+### Documentation
+
+- `SESSION_HANDOFF.md` refreshed twice this cycle — once
+  recording the HC paint + continuous-scrub polish, then
+  again as the Move Log arc shipped commit-by-commit. The
+  Resume menu's B option now traces the full arc:
+  notches → labels → footer → ESC → HC → arrow keys →
+  HC paint → continuous scrub → move log.
+
+### Stats
+
+- **1273 passing tests / 0 failing** across the workspace
+  (net +23 from v0.21.5's 1250 baseline):
+  - 2 from `d3cb1a5` (HC marker on track + notches).
+  - 2 from `2e25476` (continuous-scrub repeat-while-held +
+    release-resets-accumulator).
+  - 8 from `d6f32d3` (move-log panel init + 5 helpers + 3
+    spawn / lifecycle scenarios).
+  - 4 from `140251b` (prev rows: helper k coverage + spawn
+    cardinality + spawn texts + repaint on cursor advance).
+  - 3 from `e7345ae` (active row highlight: wrapper bg +
+    text colour + focus prefix + cursor=0 stays empty).
+  - 4 from `4437a1a` (next rows: helper k coverage + spawn
+    cardinality + spawn texts + under-fill at replay end).
+- Clippy clean across the workspace.
+
+## [0.21.5] — 2026-05-08
+
+Patch release for the post-v0.21.4 work. One through-line:
+**replay-overlay scrubbing affordances + accessibility**. v0.21.4
+shipped pause / resume / step + the WIN MOVE marker as the first
+*scrubbing-shaped* additions to the replay overlay; v0.21.5
+fills out the rest of the scrubbing UX so the player has both
+visual anchor points (notches + labels) and a complete keyboard
+control surface (Space / Esc / ← / →) for navigating a paused
+replay.
+
+Two of the six commits in this cycle are layout-changing — they
+grow the banner height from 60 px → 76 px → 92 px to make room
+for the notch labels and keybind footer. Banner geometry was
+fixed for every prior B-2 commit; this release establishes the
+"grow the container, add a flex-column child" pattern that the
+remaining B-2 sub-pieces (move-log scroller, mini-tableau
+preview) will inherit when they land.
+
+### Added
+
+- **Quarter-mark scrub-bar notches** (`fe68861`). Five 1 px
+  vertical ticks at 0 / 25 / 50 / 75 / 100 % give the player
+  visual anchor points without needing to mentally bisect the
+  bar. Pure helper `scrub_notch_positions()` returns the fixed
+  array; spawn loop sits next to the WIN MOVE marker spawn so
+  the lifecycles match. Notches paint in `BORDER_SUBTLE` (same
+  as the unfilled track) and rely on extending past the 1 px
+  track (5 px tall, anchored 2 px above the track top) for
+  visibility — same trick the WIN MOVE marker uses. Spawned
+  *after* the WIN MOVE marker so a notch and the marker
+  landing on the same percentage paint the marker on top.
+- **Percentage labels under each notch** (`d322abf`). Five
+  `0%` / `25%` / `50%` / `75%` / `100%` labels in a new 16 px
+  row beneath the 1 px scrub track give the player explicit
+  quarter-mark readouts. Banner grew from 60 → 76 px to
+  accommodate the row — first **layout-changing** commit in
+  the B-2 arc. Pure helper `scrub_notch_labels()` returns the
+  fixed array, paired index-for-index with
+  `scrub_notch_positions()`. Spawn loop applies an "endpoints
+  flush, middle three percent-anchored" positioning pattern:
+  leftmost label gets `left: 0`, rightmost gets `right: 0`,
+  middle three anchor at `left: Val::Percent(p)` since Bevy
+  0.18 UI lacks a clean CSS-style `translate-x: -50%`
+  centering primitive. Label colour is `TEXT_SECONDARY`
+  rather than the mockup's `BORDER_SUBTLE` (the latter would
+  match the notches but is too low-contrast against
+  `BG_ELEVATED_HI` to read at 12 px).
+- **Keybind-hint footer** (`1873b3f`). Vim-style mode line on
+  the left (`▌ NORMAL │ replay`) plus a keybind hint on the
+  right at the bottom edge of the banner. Banner grew from
+  76 → 92 px to fit the 16 px footer row. Surfaces every
+  wired keyboard accelerator visually so CLAUDE.md §3.3's
+  UI-first contract holds for keyboard accelerators too. The
+  footer lists *only* keybinds that are actually wired —
+  the only-wired-keybinds discipline means each release
+  cycle's hint string is a precise honest contract with the
+  player. Two pure helpers (`keybind_footer_mode_text`,
+  `keybind_footer_hint_text`) keep the static text testable.
+  1 px top border in `BORDER_SUBTLE` separates the footer
+  from the labels row.
+- **ESC keyboard accelerator for replay-stop** (`90e24d9`).
+  New `handle_stop_keyboard` system parallels
+  `handle_pause_keyboard` in shape — fires only when state
+  is `Playing`, calls `stop_replay_playback`. Cross-plugin
+  coordination via `pause_plugin::toggle_pause`: added a
+  fourth defer-if check
+  (`replay_state.is_some_and(|s| s.is_playing())`) right
+  after the existing `other_modal_scrims` check so ESC
+  during active replay belongs to the replay overlay, not
+  the pause modal.
+- **HC-mode coverage for the keybind-footer top border**
+  (`23902cd`).
+  `HighContrastBorder::with_default(BORDER_SUBTLE)` marker
+  on the footer's border-carrying Node so the existing
+  `apply_high_contrast_borders` system bumps the 1 px top
+  border from `#505050` → `#a0a0a0` when
+  `Settings::high_contrast_mode` is on. Without the marker
+  the footer reads as floating loose under HC because the
+  border that anchors it to the labels row is
+  near-invisible.
+- **← / → keyboard accelerators for paused stepping**
+  (`e5c4f51`). New `step_backwards_replay_playback` in
+  `replay_playback.rs` decrements the cursor and dispatches
+  `UndoRequestEvent`; the game's `handle_undo` reads it
+  next frame to reverse its most-recent move. Hooks the
+  existing undo system rather than replaying-forward-from-
+  zero — every replay-applied move pushes to the undo stack
+  the same way a player move would, so undo is the right
+  reversal primitive. Both arrow keys are paused-only via
+  the same destructure-gate pattern the forward step uses.
+  The mockup labels these `[← →] scrub`; single-move step
+  is the closest behaviour shippable today, so the footer
+  hint reads `[← →] step` — only-wired-keybinds discipline.
+
+### Changed
+
+- **Banner height grew 60 → 76 → 92 px** across two
+  layout-changing commits (`d322abf` then `1873b3f`). Top
+  row's `flex_grow: 1.0` still consumes 59 px so the
+  existing content (label / progress chip / buttons) has
+  the same vertical space; the new rows (16 px labels +
+  16 px footer) extend the banner downward into the
+  gameplay area. Banner geometry is now mutable — every
+  prior B-2 commit fit inside fixed 60 px space.
+- **Keybind-footer hint text grew alongside the wirings**:
+  `[SPACE] pause/resume` →
+  `[SPACE] pause/resume · [ESC] stop` →
+  `[SPACE] pause/resume · [ESC] stop · [← →] step`.
+- **`pause_plugin::toggle_pause` now defers when a replay
+  is active** (`90e24d9`). Adds a fourth defer-if check to
+  the existing modal-stack pattern.
+- **`ReplayOverlayPlugin` registers
+  `add_message::<UndoRequestEvent>()`** (`e5c4f51`).
+  Defensive registration so the plugin runs cleanly under
+  `MinimalPlugins` without `GamePlugin` attached.
+
+### Documentation
+
+- `SESSION_HANDOFF.md` refreshed five times this cycle.
+  The B option in the Resume menu now traces the full arc:
+  notches → labels → footer → ESC → HC → arrow keys.
+- The pre-existing `daily_challenge` warning test that
+  fails when wall-clock UTC is within 30 minutes of
+  midnight is documented in this cycle's handoff. Same
+  shape as the earlier `winnable_seed_search` flake —
+  time-dependent, deterministically passes outside the
+  trigger window.
+
+### Stats
+
+- **1250 total tests / 1249 passing / 1 pre-existing
+  time-dependent flake** across the workspace (net +22 from
+  v0.21.4's 1228 baseline):
+  - 4 from `fe68861` (scrub-notch coverage)
+  - 4 from `d322abf` (notch-label coverage)
+  - 4 from `1873b3f` (keybind-footer coverage)
+  - 3 from `90e24d9` (ESC-accelerator coverage)
+  - 1 from `23902cd` (HC-marker coverage)
+  - 6 from `e5c4f51` (arrow-keyboard coverage)
+- **Pre-existing flake**:
+  `daily_challenge_plugin::tests::check_system_fires_warning_event_only_once_per_day`
+  fails when wall-clock UTC is within 30 minutes of
+  midnight. Verified pre-existing by stash-and-retest
+  before each commit. Will pass deterministically outside
+  the trigger window. Not introduced by this release.
+- Clippy clean across the workspace.
+
 ## [0.21.4] — 2026-05-08
 
 Patch release for the post-v0.21.3 work. One through-line:

SESSION_HANDOFF.md

@@ -1,91 +1,85 @@
 # Solitaire Quest — Session Handoff
 
-**Last updated:** 2026-05-08 — **v0.21.3 cut and tagged at
-`3d92a91`**, working tree clean, all post-tag work pushed to
+**Last updated:** 2026-05-08 — **v0.21.6 cut and tagged at
+`f63db76`**, working tree clean, all post-tag work pushed to
 origin.
 
-v0.21.3 is a patch release with one through-line: **accessibility
-arc closure**. v0.21.2 explicitly carved out "dynamic-paint sites"
-(HUD action buttons, modal buttons, radial menu rim) on the
-assumption that their existing paint cycles would race the
-central `update_high_contrast_borders` system. v0.21.3 walks the
-actual code, finds the carve-out was over-cautious, and closes
-it. Bonus: the first real consumer of `ToastVariant::Warning`
-also lands here, making the `ToastVariant` enum fully load-bearing
-(every variant has at least one driver).
+v0.21.6 is a patch release with through-line:
+**Move Log panel + scrub-UX polish**. v0.21.5 closed out the
+keyboard-accelerator surface (Space / Esc / ← / →) and the
+keybind footer; v0.21.6 builds on that with two parallel
+threads — accessibility + scrub-on-hold polish for the v0.21.5
+surfaces, plus a brand-new Move Log panel anchored to the
+viewport's bottom edge that gives players a 5-row recent-and-
+upcoming move history alongside the existing top-edge banner.
 
-Full v0.21.3 detail lives in `CHANGELOG.md` § [0.21.3]. This
+The Move Log panel is the first replay-overlay surface that
+*isn't* attached to the banner — it lives at a separate screen
+anchor (`bottom: 0`) with its own spawn/despawn lifecycle.
+Establishes the "multi-anchor replay UI" pattern that the
+remaining B-2 sub-piece (mini-tableau preview) will inherit.
+
+Six commits on the B-2 replay screen-takeover redesign arc land
+here, bringing the post-v0.21.4 total to 12. The remaining B-2
+piece — mini-tableau preview that dims the gameplay tableau
+during replay — is the only major sub-piece still open.
+
+Full v0.21.6 detail lives in `CHANGELOG.md` § [0.21.6]. This
 file from here on focuses on what's *open* post-cut and how to
 resume.
 
 ## Status at pause
 
 - **HEAD locally:** see `git rev-parse HEAD`. The cut commit is
-  `3d92a91`; post-cut work on B-2 (`ab857bb` data field +
-  `52befa6` WIN MOVE marker UI + `fbe48ac` playback controls)
-  rides on top of that.
-- **HEAD on origin:** matches local. v0.21.3 is fully on origin.
+  `f63db76`; any post-cut docs edits ride on top of that.
+- **HEAD on origin:** matches local. v0.21.6 is fully on origin.
 - **Working tree:** clean. No WIP outstanding.
 - **`artwork/` directory:** still untracked. Intentional.
 - **Build:** `cargo clippy --workspace --all-targets -- -D warnings`
   clean.
-- **Tests:** **1228 passing / 0 failing** across the workspace
-  (1207 from v0.21.3's stats + 5 from `ab857bb`'s
-  `win_move_index` coverage + 8 from `52befa6`'s WIN MOVE marker
-  pure-helper truth-table + spawn lifecycle + 8 from `fbe48ac`'s
-  pause / step / keyboard accelerator coverage).
-- **Tags on origin:** `v0.9.0` through `v0.21.3`. v0.21.3 is on
-  `3d92a91`; v0.21.2 stays on `f23df3b`; v0.21.1 stays on
-  `daa655a`; v0.21.0 stays on `04f9bf9`; v0.20.0 stays on
-  `41a009a`.
+- **Tests:** **1273 passing / 0 failing** across the workspace.
+  Detail in `CHANGELOG.md` § [0.21.6] § Stats.
+- **Tags on origin:** `v0.9.0` through `v0.21.6`. v0.21.6 is on
+  `f63db76`; v0.21.5 stays on `a2432df`; v0.21.4 stays on
+  `23ff62c`; v0.21.3 stays on `3d92a91`; v0.21.2 stays on
+  `f23df3b`; v0.21.1 stays on `daa655a`; v0.21.0 stays on
+  `04f9bf9`; v0.20.0 stays on `41a009a`.
 
-## Since the v0.21.3 cut
+## Since the v0.21.6 cut
 
-- **`ab857bb` — `Replay::win_move_index` data field landed.**
-  First finite step toward the B-2 replay screen-takeover
-  redesign. Additive optional `Option<usize>` on `Replay` with
-  `#[serde(default)]` so older `latest_replay.json` /
-  `replays.json` files load unchanged (no schema bump). Populated
-  at the live recording site via a new `with_win_move_index`
-  builder; for fresh recordings the value is always
-  `Some(moves.len() - 1)` because recording freezes on win, but
-  storing it explicitly lets the playback UI read the WIN MOVE
-  position directly without re-deriving on every render. 5 new
-  tests (1207 → 1212): default, builder set / set-None, on-disk
-  round-trip, legacy-JSON-loads-with-None backward-compat.
-- **`52befa6` — WIN MOVE marker on the scrub bar.** Second
-  commit on B-2 — the UI that consumes the data field. New
-  `ReplayOverlayWinMoveMarker` component spawned as a sibling
-  to `ReplayOverlayScrubFill` under the 1px scrub track,
-  absolute-positioned at `replay.win_move_index / total` along
-  the bar. Painted in `STATE_SUCCESS` (green) so the marker
-  reads as "this is where the win lives." Pure helper
-  `win_move_marker_pct` returns `None` for any state where the
-  marker shouldn't draw (Inactive, Completed, replay missing
-  the field, empty move list); percentage clamps to `[0, 100]`
-  defensively. Lifecycle is spawn-time only — the marker is
-  immutable during a single playback because the underlying
-  `Replay` doesn't change while `Playing`. Despawned with the
-  overlay tree on transition back to `Inactive`. 8 new tests
-  (1212 → 1220): pure-helper truth table + spawn-presence /
-  spawn-absence / despawn-lifecycle observables.
-- **`fbe48ac` — playback controls (pause / resume / step).**
-  Third commit on B-2. New `paused: bool` field on
-  `ReplayPlaybackState::Playing`; `tick_replay_playback` skips
-  the `secs_to_next` decrement entirely while paused so cursor
-  and timer freeze together. New public API:
-  `toggle_pause_replay_playback` and `step_replay_playback`
-  (the latter hard-gated to `Playing { paused: true }` so
-  manual stepping can't race the tick loop). UI: Pause /
-  Resume button (label repaints reactively via
-  `update_pause_button_label` which walks `Children` from
-  marker to inner `Text`) + Step button + Space keyboard
-  accelerator. Existing 25 `Playing { ... }` construction
-  sites across tests gained `paused: false` mechanically.
-  8 new tests (1220 → 1228): label truth table, label repaint
-  on state change, click-toggles-paused, step advances exactly
-  one cursor with paused preserved, step-while-running no-op,
-  Space toggles paused.
+No threads in flight. Working tree clean as of 2026-05-08. New
+work since the cut would land here as commit narratives; for
+the v0.21.6 contents themselves, see `CHANGELOG.md` § [0.21.6].
+
+Open next-step menu (Move Log + scrub-UX + keyboard accelerator
+coverage + accessibility are all complete):
+1. **Mini-tableau preview** — the only remaining major B-2
+   sub-piece. Mockup shows a 240 px-tall band at 50 % opacity
+   showing the gameplay tableau peeking through the replay
+   chrome. Implementation needs to add a settings-aware dim
+   overlay or alpha modulation on the tableau cards during
+   replay. Architectural — touches `card_plugin` rendering.
+   Multi-session.
+2. **Move Log auto-scroll** — only relevant if the panel's
+   row count grows beyond the current 5-row fixed window.
+   Currently the prev-2 / active / next-2 layout fits all
+   visible content, so auto-scroll is unneeded. Becomes
+   relevant if a future commit expands the panel's row
+   capacity (e.g. 10-row scrolling list).
+3. **Polish: notch label centering.** Bevy 0.18 lacks a
+   clean `translate-x: -50%` primitive so middle three
+   labels sit slightly right-of-notch. Could use a child
+   Text wrapper with computed left-margin compensation.
+   Tiny commit, requires visual review.
+4. **Polish: WIN MOVE marker HC bump.** Currently uses
+   `STATE_SUCCESS` lime which stays visible under HC, but a
+   contrast bump under HC would make it even more legible
+   alongside the bumped notches. Optional.
+
+Recommended order: option 1 (mini-tableau preview) is the
+big remaining piece that closes B-2 — best tackled in a
+fresh session because it crosses into `card_plugin`. Options
+3 and 4 are visual polish that benefit from user review.
 
 ## Open punch list
 
@@ -126,10 +120,21 @@ palette refresh all shipped in v0.20.0 + v0.21.0. What stays open:
   shipped in v0.21.2 (`2fb2d63`). The WIN MOVE scrub-bar marker
   shipped post-v0.21.3 in `ab857bb` (data field) + `52befa6`
   (UI). Playback controls (pause / resume / step + Space
-  accelerator) shipped post-v0.21.3 in `fbe48ac`. What still
-  needs to land: a move-log scroller and a mini-tableau
-  preview — both screen-takeover-only pieces that need a
-  larger layout reflow than the existing banner can carry.
+  accelerator) shipped post-v0.21.3 in `fbe48ac`. v0.21.5
+  bundled six more commits under "replay-overlay scrubbing
+  affordances + accessibility" (scrub notches + labels +
+  keybind footer + ESC and ← / → accelerators + HC border).
+  v0.21.6 bundled six more under "Move Log panel + scrub-UX
+  polish" — bottom-edge Move Log panel with prev/active/next
+  rows + active highlight, HC-mode coverage for the scrub
+  track + notches, continuous scrub on key-held arrows. Banner
+  height grew 60 → 76 → 92 px across two layout-changing
+  commits in v0.21.5; Move Log panel grew 56 → 84 → 112 px
+  across the v0.21.6 move-log commits. Per-commit detail in
+  `CHANGELOG.md` § [0.21.5] and § [0.21.6]. The only major
+  B-2 piece left is the mini-tableau preview — the mockup's
+  "Game Peek Band" at 50 % opacity. Architectural; touches
+  `card_plugin` rendering.
   Multi-session.
 - *Floating `MOVE N/M` chip above the focused card during
   playback — closed 2026-05-08 by `2fb2d63`.* World-space
@@ -273,20 +278,23 @@ into a v0.21.1 / v0.22.0 cut.
 ```
 You are a senior Rust + Bevy developer working on Solitaire Quest.
 Working directory: <Rusty_Solitaire clone path on this machine>.
-Branch: master. v0.21.3 is tagged at 3d92a91 (cut 2026-05-08, a
-patch release rolling up the accessibility-arc closure: HC reaches
-the previously-carved-out dynamic-paint sites, and the first real
-consumer of `ToastVariant::Warning` lands as the daily-challenge
-expiry toast). v0.21.2 stays at f23df3b, v0.21.1 at daa655a,
-v0.21.0 at 04f9bf9. Working tree clean. See CHANGELOG.md §
-[0.21.3] for full detail.
+Branch: master. v0.21.6 is tagged at f63db76 (cut 2026-05-08, a
+patch release rolling up Move Log panel + scrub-UX polish:
+brand-new bottom-edge Move Log panel with prev / active / next
+row context + active-row highlight, plus HC-mode coverage for
+scrub track + notches and continuous scrub on key-held arrow
+keys). v0.21.5 stays at a2432df, v0.21.4 at 23ff62c, v0.21.3
+at 3d92a91, v0.21.2 at f23df3b, v0.21.1 at daa655a, v0.21.0 at
+04f9bf9. Working tree clean. See CHANGELOG.md § [0.21.6] for
+full detail.
 
-State: HEAD locally — see `git rev-parse HEAD`. All workspace tests
-pass (1207+; check with `cargo test --workspace`), clippy clean.
+State: HEAD locally — see `git rev-parse HEAD`. The cut commit
+is f63db76; any post-cut docs edits ride on top of that.
+Workspace tests: 1273 passing / 0 failing. Clippy clean.
 
 READ FIRST (in order, before doing anything):
   1. SESSION_HANDOFF.md  — this file
-  2. CHANGELOG.md        — [0.21.3] section is the most recent cut
+  2. CHANGELOG.md        — [0.21.6] section is the most recent cut
   3. CLAUDE.md           — unified-3.0 rule set
   4. CLAUDE_SPEC.md      — formal architecture spec
   5. ARCHITECTURE.md     — crate responsibilities + data flow
@@ -306,18 +314,22 @@ DECISION TO ASK THE PLAYER FIRST:
      tests can't catch. Likely surfaces JNI ClipboardManager
      and Android Keystore stubs that need real bridges. Larger
      scope; needs an Android device or emulator running.
-  B. Replay-overlay screen-takeover redesign — multi-session
-     work. Three sub-pieces shipped post-v0.21.3: WIN MOVE
-     marker (`ab857bb` data field + `52befa6` UI), playback
-     controls (`fbe48ac` pause/resume/step + Space). What
-     still needs to land: a move-log scroller and a
-     mini-tableau preview — both layout-heavy pieces that need
-     more vertical real estate than the current banner-only
-     overlay carries, so the natural next finite step is the
-     screen-takeover layout itself (mockup at
-     `docs/ui-mockups/replay-overlay-mobile.html`). The
-     smaller floating-MOVE-chip piece shipped in v0.21.2
-     (`2fb2d63`).
+  B. Replay-overlay screen-takeover redesign — nearly complete
+     after 12 commits across v0.21.4-6. Scrub bar with notches
+     + labels + WIN MOVE marker, pause / resume / step / stop
+     buttons, Space + Esc + ← / → keyboard accelerators with
+     continuous scrub on hold, keybind-hint footer, full HC-mode
+     coverage on the banner pieces, and a brand-new bottom-edge
+     Move Log panel with a 5-row prev/active/next window all
+     ship. The only remaining major B-2 sub-piece is the
+     **mini-tableau preview** — the mockup's "Game Peek Band"
+     at 50 % opacity showing the tableau through the replay
+     chrome. Implementation needs a settings-aware dim overlay
+     or alpha modulation on the tableau cards during replay.
+     Architectural — touches `card_plugin` rendering. Best
+     tackled in a fresh session because it crosses into a
+     plugin the recent B-2 work hasn't touched. Mockup at
+     `docs/ui-mockups/replay-overlay-mobile.html`.
   C. Phase 8 (sync) — local storage scaffolding, self-hosted
      Axum server, `SolitaireServerClient` impl, GPGS stub
      wired into Settings. The biggest open arc by scope; rolls

solitaire_engine/src/pause_plugin.rs

@@ -30,6 +30,7 @@ use crate::events::{
 use crate::font_plugin::FontResource;
 use crate::game_plugin::{GameOverScreen, GameStatePath};
 use crate::progress_plugin::ProgressResource;
+use crate::replay_playback::ReplayPlaybackState;
 use crate::resources::{DragState, GameStateResource};
 use crate::selection_plugin::{SelectionKeySet, SelectionState};
 use crate::settings_plugin::{SettingsChangedEvent, SettingsResource, SettingsStoragePath};
@@ -154,6 +155,7 @@ fn toggle_pause(
     mut drag: Option<ResMut<DragState>>,
     mut changed: MessageWriter<StateChangedEvent>,
     selection: Option<Res<SelectionState>>,
+    replay_state: Option<Res<ReplayPlaybackState>>,
 ) {
     let PauseModalQueries {
         pause_screens: screens,
@@ -184,6 +186,15 @@ fn toggle_pause(
     if !other_modal_scrims.is_empty() {
         return;
     }
+    // If a replay is currently playing, let `replay_overlay::handle_stop_keyboard`
+    // own the Esc press — that handler stops the replay. Without this guard a
+    // single Esc both stops the replay AND opens the pause modal on top of the
+    // (now empty) board, leaving the player on a screen they didn't ask for.
+    // The HUD-button path is gated too; clicking Pause while watching a replay
+    // is almost always an accident.
+    if replay_state.is_some_and(|s| s.is_playing()) {
+        return;
+    }
     // If a card is currently selected, let SelectionPlugin handle this Escape
     // (it will clear the selection). Pause must not also open in the same frame.
     if selection.is_some_and(|s| s.selected_pile.is_some()) {

solitaire_engine/src/replay_playback.rs

@@ -42,7 +42,7 @@
 use bevy::prelude::*;
 use solitaire_data::{Replay, ReplayMove};
 
-use crate::events::{DrawRequestEvent, MoveRequestEvent, StateChangedEvent};
+use crate::events::{DrawRequestEvent, MoveRequestEvent, StateChangedEvent, UndoRequestEvent};
 use crate::game_plugin::{GameMutation, RecordingReplay};
 use crate::resources::GameStateResource;
 use crate::settings_plugin::SettingsResource;
@@ -284,6 +284,52 @@ pub fn step_replay_playback(
     true
 }
 
+/// Steps the replay **backwards** by exactly one move while paused.
+///
+/// Strategy: the live game's undo system is the source of truth for
+/// reversing moves. Every move the replay forward-stepped (via
+/// [`step_replay_playback`] or the auto-advance loop in
+/// [`tick_replay_playback`]) was dispatched as a canonical
+/// [`MoveRequestEvent`] / [`DrawRequestEvent`], which the game
+/// applied and pushed onto its undo stack. So a backwards step here
+/// is simply: decrement the cursor (so the about-to-apply move
+/// re-points at the one we're rewinding past) and fire an
+/// [`UndoRequestEvent`] so the game reverses its most-recent move
+/// next frame.
+///
+/// Hard-gated to the paused state via destructure pattern —
+/// matches the existing [`step_replay_playback`] gate so the
+/// player can only scrub one direction at a time and the tick
+/// loop never races a manual rewind.
+///
+/// Returns `false` and is a no-op in three cases:
+/// - State isn't `Playing` (no replay attached).
+/// - State is `Playing` but not paused (the tick loop owns the cursor).
+/// - Cursor is already at 0 (nothing to rewind past).
+///
+/// Returns `true` on a successful step; the actual game-state
+/// reversal happens next frame when `handle_undo` reads the
+/// `UndoRequestEvent`.
+pub fn step_backwards_replay_playback(
+    state: &mut ResMut<ReplayPlaybackState>,
+    undo_writer: &mut MessageWriter<UndoRequestEvent>,
+) -> bool {
+    let ReplayPlaybackState::Playing {
+        cursor,
+        paused: true,
+        ..
+    } = state.as_mut()
+    else {
+        return false;
+    };
+    if *cursor == 0 {
+        return false;
+    }
+    *cursor -= 1;
+    undo_writer.write(UndoRequestEvent);
+    true
+}
+
 /// Tick system. Runs every frame; only does work when
 /// [`ReplayPlaybackState::is_playing`].
 ///

solitaire_engine/src/settings_plugin.rs

@@ -34,7 +34,8 @@ use crate::ui_modal::{
 };
 use crate::ui_tooltip::Tooltip;
 use crate::ui_theme::{
-    BG_BASE, BG_ELEVATED, BG_ELEVATED_HI, BORDER_SUBTLE, BORDER_SUBTLE_HC, HighContrastBorder,
+    BG_BASE, BG_ELEVATED, BG_ELEVATED_HI, BORDER_SUBTLE, BORDER_SUBTLE_HC, HighContrastBackground,
+    HighContrastBorder,
     RADIUS_SM, SPACE_2, STATE_SUCCESS, TEXT_PRIMARY, TEXT_SECONDARY, TYPE_BODY, TYPE_BODY_LG,
     TYPE_CAPTION, VAL_SPACE_2, VAL_SPACE_3, Z_MODAL_PANEL,
 };
@@ -365,6 +366,7 @@ impl Plugin for SettingsPlugin {
                     update_color_blind_text,
                     update_high_contrast_text,
                     update_high_contrast_borders,
+                    update_high_contrast_backgrounds,
                     update_reduce_motion_text,
                     update_tooltip_delay_text,
                     update_time_bonus_multiplier_text,
@@ -674,6 +676,41 @@ fn update_high_contrast_borders(
     }
 }
 
+/// Repaints `BackgroundColor` on every entity tagged with
+/// [`HighContrastBackground`] based on `Settings::high_contrast_mode`.
+/// Off → the marker's `default_color`; on → `BORDER_SUBTLE_HC`
+/// (`#a0a0a0`). Compares against the current background and only
+/// mutates when different so Bevy's change-detection doesn't trigger
+/// repaints every frame.
+///
+/// Parallel to [`update_high_contrast_borders`]. Same on/off rule,
+/// same change-suppression idiom, different colour channel —
+/// `BackgroundColor` for tick marks, decorative strips, fine
+/// separators that paint their shape directly rather than via a
+/// `BorderColor` on a wider Node.
+///
+/// Tagged sites in v0.21.x: the replay overlay's 1 px scrub track
+/// + 5 quarter-mark notch ticks (`replay_overlay::spawn_overlay`).
+///
+/// More sites can be tagged in follow-ups by adding
+/// `HighContrastBackground::with_default(...)` to their spawn tuple.
+pub(crate) fn update_high_contrast_backgrounds(
+    settings: Res<SettingsResource>,
+    mut backgrounds: Query<(&HighContrastBackground, &mut BackgroundColor)>,
+) {
+    let high_contrast = settings.0.high_contrast_mode;
+    for (marker, mut bg) in backgrounds.iter_mut() {
+        let target = if high_contrast {
+            BORDER_SUBTLE_HC
+        } else {
+            marker.default_color
+        };
+        if bg.0 != target {
+            *bg = BackgroundColor(target);
+        }
+    }
+}
+
 fn update_reduce_motion_text(
     settings: Res<SettingsResource>,
     mut text_nodes: Query<&mut Text, With<ReduceMotionText>>,

solitaire_engine/src/ui_theme.rs

@@ -252,6 +252,35 @@ impl HighContrastBorder {
     }
 }
 
+/// Marker for entities whose [`BackgroundColor`] should swap to
+/// [`BORDER_SUBTLE_HC`] when `Settings::high_contrast_mode` is on.
+/// Parallel to [`HighContrastBorder`] but for sites that paint their
+/// shape via `BackgroundColor` rather than `BorderColor` —
+/// `bevy::ui` 1 px decorative strips, tick marks, fine separators
+/// often render as tiny full-bleed `Node`s, not as borders, so the
+/// border-marker pattern doesn't apply.
+///
+/// `default_color` records the off-state colour the entity was
+/// spawned with so the system can revert when HC is toggled back
+/// off. The accompanying paint system is
+/// [`update_high_contrast_backgrounds`](crate::settings_plugin::update_high_contrast_backgrounds).
+///
+/// [`BackgroundColor`]: bevy::prelude::BackgroundColor
+#[derive(bevy::prelude::Component, Debug, Clone, Copy)]
+pub struct HighContrastBackground {
+    /// Background colour to use when high-contrast mode is *off* —
+    /// the site's normal idle / active-state colour.
+    pub default_color: bevy::prelude::Color,
+}
+
+impl HighContrastBackground {
+    /// Convenience constructor —
+    /// `HighContrastBackground::with_default(BORDER_SUBTLE)`.
+    pub const fn with_default(default_color: bevy::prelude::Color) -> Self {
+        Self { default_color }
+    }
+}
+
 /// Strong border — hover outline, focused button, active popover.
 /// `outline` from the design system. `#505050`.
 pub const BORDER_STRONG: Color = Color::srgba(0.314, 0.314, 0.314, 1.0);