docs: cut v0.21.6 — Move Log panel + scrub-UX polish

Patch release rolling up six post-v0.21.5 commits under the
through-line "Move Log panel + scrub-UX polish":

- d3cb1a5: HC-mode coverage for scrub track + notches
- 2e25476: continuous scrub on key-held ← / → at 100ms cadence
- d6f32d3: Move Log panel + active row (header + format helpers)
- 140251b: 2 prev rows above active
- e7345ae: active-row highlight with ACCENT_PRIMARY background
- 4437a1a: 2 next rows below active

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.

Panel grows 56 → 84 → 112 px across the four move-log commits.
HighContrastBackground primitive lifted to ui_theme parallel
to HighContrastBorder; settings_plugin gains
update_high_contrast_backgrounds for the BackgroundColor
repaint cycle. Continuous scrub uses a per-key accumulator
resource (ReplayScrubKeyHold) gated on SCRUB_REPEAT_INTERVAL_SECS
(0.1s).

Tests: 1250 → 1273 (+23 net new). Clippy clean.

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

CHANGELOG.md

@@ -6,9 +6,121 @@ project follows [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased]
 
-No threads in flight. v0.21.5 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:

SESSION_HANDOFF.md

@@ -1,198 +1,101 @@
 # Solitaire Quest — Session Handoff
 
-**Last updated:** 2026-05-08 — **v0.21.4 cut and tagged at
+**Last updated:** 2026-05-08 — **v0.21.5 cut and tagged at
-`23ff62c`**, working tree clean, all post-tag work pushed to
+`a2432df`**, working tree clean, all post-tag work pushed to
 origin.
 
-v0.21.4 is a patch release with one through-line:
+v0.21.5 is a patch release with one through-line:
-**replay-scrubbing accessibility**. The replay overlay used to be
+**replay-overlay scrubbing affordances + accessibility**.
-pure-passive — start, watch, wait. v0.21.4 adds the scaffolding
+v0.21.4 shipped pause / resume / step + the WIN MOVE marker as
-for *navigating within* a replay: a WIN MOVE marker on the scrub
+the first scrubbing-shaped additions to the replay overlay;
-bar so the player can see at a glance where the winning move
+v0.21.5 fills out the rest of the scrubbing UX so the player
-sits, plus pause / resume / step controls (with a Space keyboard
+has both visual anchor points (notches + labels) and a complete
-accelerator) so they can stop on any move and inspect the board.
+keyboard control surface (Space / Esc / ← / →) for navigating a
-Also lands the additive `Replay::win_move_index: Option<usize>`
+paused replay.
-data field that makes the marker possible — serde-default so
-older on-disk replays load with `None` and simply don't get a
-marker (no schema bump).
 
-Three commits on the B-2 replay screen-takeover redesign arc
+Six commits on the B-2 replay screen-takeover redesign arc land
-land here. The remaining sub-pieces (screen-takeover layout,
+here. Two of them are layout-changing — banner height grew
-move-log scroller, mini-tableau preview) share a layout-reflow
+60 → 76 → 92 px to make room for the notch labels and keybind
-prerequisite the banner can't carry, so they're deferred to a
+footer. Banner geometry was fixed for every prior B-2 commit;
-future cycle as a single multi-session arc.
+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.
 
-Full v0.21.4 detail lives in `CHANGELOG.md` § [0.21.4]. This
+Full v0.21.5 detail lives in `CHANGELOG.md` § [0.21.5]. 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
-  `23ff62c`; any post-cut docs edits ride on top of that.
+  `a2432df`; any post-cut docs edits ride on top of that.
-- **HEAD on origin:** matches local. v0.21.4 is fully on origin.
+- **HEAD on origin:** matches local. v0.21.5 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:** **1250 total / 1249 passing / 1 pre-existing
+- **Tests:** **1254 passing / 0 failing** across the workspace
-  time-dependent flake** across the workspace
+  (1250 in v0.21.5 + 2 from `d3cb1a5`'s HC-marker tests + 2
-  (1228 in v0.21.4 + 4 from `fe68861`'s scrub-notch tests + 4
+  from `2e25476`'s continuous-scrub tests). The
-  from `d322abf`'s notch-label tests + 4 from `1873b3f`'s
+  time-dependent `daily_challenge` flake noted in v0.21.5's
-  keybind-footer tests + 3 from `90e24d9`'s ESC-accelerator
+  CHANGELOG passes again (UTC clock has moved past the
-  tests + 1 from `23902cd`'s HC-marker test + 6 from
+  trigger window). Detail in `CHANGELOG.md` § [0.21.5] § Stats
-  `e5c4f51`'s arrow-keyboard tests). The flake is
+  for the v0.21.5 baseline; post-cut delta tracked in this
-  `daily_challenge_plugin::tests::check_system_fires_warning_event_only_once_per_day`
+  file's Since-cut log.
-  — fails when wall-clock UTC is within 30 minutes of midnight
+- **Tags on origin:** `v0.9.0` through `v0.21.5`. v0.21.5 is on
-  (the daily-expiry warning window the test asserts against).
+  `a2432df`; v0.21.4 stays on `23ff62c`; v0.21.3 stays on
-  Verified pre-existing. Detail in `CHANGELOG.md` § [0.21.4]
-  § Stats; post-cut delta tracked here.
-- **Tags on origin:** `v0.9.0` through `v0.21.4`. v0.21.4 is 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`.
-- **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`.
 
-## Since the v0.21.4 cut
+## Since the v0.21.5 cut
 
-- **`fe68861` — `feat(replay): add quarter-mark notches to scrub
+- **`d3cb1a5` — `feat(replay): HC-mode coverage for scrub
-  bar`.** First finite step toward B-2's screen-takeover layout.
+  track + notches`.** Adds a parallel primitive to ui_theme
-  Five 1px vertical ticks at 0/25/50/75/100 % give the player
+  (`HighContrastBackground` marker carrying `default_color`)
-  visual anchor points without needing to mentally bisect the
+  and a paint system in settings_plugin
-  bar. Pure helper `scrub_notch_positions()` returns the fixed
+  (`update_high_contrast_backgrounds`) that mirrors the
-  array; spawn loop lives next to the WIN MOVE marker spawn so
+  existing border-marker pattern but targets `BackgroundColor`
-  the lifecycles match. Notches paint in `BORDER_SUBTLE`
+  instead of `BorderColor`. Tags the 1 px scrub track Node and
-  (matches unfilled-track colour) and rely on extending past the
+  all five quarter-mark notch ticks with the new marker so
-  1px track (5px tall, anchored 2px above track top) for
+  they bump from `BORDER_SUBTLE` (#505050) → `BORDER_SUBTLE_HC`
-  visibility — same trick the WIN MOVE marker uses. Spawned
+  (#a0a0a0) under HC mode. Scrub fill (ACCENT_PRIMARY) and
-  *after* the WIN MOVE marker so a notch and the marker landing
+  WIN MOVE marker (STATE_SUCCESS) don't get the marker —
-  on the same percentage paint the marker on top. Mirrors the
+  accent and state colours are already saturated. 2 new tests;
-  notch ladder in `docs/ui-mockups/replay-overlay-mobile.html`.
+  1250 → 1252.
-  4 new tests; 1228 → 1232.
+- **`2e25476` — `feat(replay): continuous scrub on key-held
-- **`d322abf` — `feat(replay): add percentage labels under
+  arrow keys`.** Holding ← or → now triggers continuous step
-  scrub-bar notches`.** First **layout-changing** commit in B-2's
+  at 100 ms cadence (10 steps/sec) — matches the mockup's
-  screen-takeover arc. Banner height grew from 60 → 76 px to make
+  `[← →] scrub` terminology while keeping single-press =
-  room for a 16 px label row beneath the 1 px scrub track; the
+  single-step semantics. Per-key accumulators in a new
-  top row's `flex_grow: 1.0` still consumes the same 59 px so no
+  `ReplayScrubKeyHold` resource; `just_pressed` events bypass
-  ripples on existing content. Pure helper `scrub_notch_labels()`
+  the accumulator and fire immediately. Release resets to 0
-  returns the fixed `["0%", "25%", "50%", "75%", "100%"]` array,
+  so the next fresh press fires immediately rather than at
-  paired index-for-index with `scrub_notch_positions()`. Spawn
+  half-interval. Footer text unchanged (`[← →] step`) —
-  loop applies an "endpoints flush, middle three percent-anchored"
+  held-key scrub is a discoverable enhancement to the same
-  positioning pattern (Bevy 0.18 UI has no clean
+  keybind, not a new keybind. 2 new tests using
-  `translate-x: -50%` primitive, so endpoints flush against
+  `TimeUpdateStrategy::ManualDuration`; 1252 → 1254.
-  banner edges and middle three accept slight right-of-notch
-  offset). Label colour is `TEXT_SECONDARY` (mockup's
-  `BORDER_SUBTLE` reads as too low-contrast at 12 px against
-  `BG_ELEVATED_HI`). 4 new tests; 1232 → 1236.
-- **`1873b3f` — `feat(replay): add keybind-hint footer to
-  overlay banner`.** Second layout-changing commit in B-2's arc.
-  Banner grew from 76 → 92 px to fit a 16 px footer row at the
-  bottom edge with a vim-style mode line on the left
-  (`▌ NORMAL │ replay`) and a keybind-hint on the right
-  (`[SPACE] pause/resume`). Surfaces the existing Space
-  accelerator visually so CLAUDE.md §3.3's UI-first contract
-  holds for keyboard accelerators too. Footer lists *only
-  wired* keybinds — future commits that wire ESC for stop or
-  ← / → for prev/next will extend the right-hand text in
-  lockstep. Two pure helpers (`keybind_footer_mode_text`,
-  `keybind_footer_hint_text`) keep the static text testable;
-  shared `font_handle_for_labels` clone covers both label and
-  footer text spawns. 1px top border in `BORDER_SUBTLE`
-  separates the footer from the labels row. 4 new tests;
-  1236 → 1240.
-- **`90e24d9` — `feat(replay): wire ESC accelerator for stop,
-  gate pause modal`.** ESC during an active replay now stops it
-  (mirrors the Stop button click). New `handle_stop_keyboard`
-  system in `replay_overlay.rs` parallels `handle_pause_keyboard`
-  in shape. 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
-  `other_modal_scrims` and before `selection`. Symmetric to the
-  existing modal-stack defer pattern. Footer hint extended from
-  `[SPACE] pause/resume` → `[SPACE] pause/resume · [ESC] stop`
-  in lockstep with the wiring; the only-wired-keybinds
-  discipline holds. 3 new tests + 1 updated helper-pin test;
-  1240 → 1243.
-- **`23902cd` — `feat(replay): HC-mode coverage for
-  keybind-footer top border`.** Tag the footer's border-carrying
-  Node with `HighContrastBorder::with_default(BORDER_SUBTLE)` so
-  the existing `apply_high_contrast_borders` system bumps the
-  1 px top border from `#505050` → `#a0a0a0` under HC mode.
-  Footer text colours don't need bumps —
-  `TEXT_SECONDARY` (`#a0a0a0`) is already at `BORDER_SUBTLE_HC`
-  luminance by design (no `TEXT_SECONDARY_HC` constant exists).
-  The 1 px scrub track, notch ticks, and WIN MOVE marker render
-  via `BackgroundColor` (not `BorderColor`) so the marker
-  doesn't apply — HC coverage for those would need a
-  settings-aware paint system (precedent: `radial_rim_outline`
-  in `radial_menu`) and is deferred. 1 new test; 1243 → 1244.
-- **`e5c4f51` — `feat(replay): wire ← / → keyboard accelerators
-  for paused stepping`.** 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 — hooking the existing
-  undo system rather than replaying forward from cursor 0
-  (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. Footer hint
-  extended in lockstep:
-  `[SPACE] pause/resume · [ESC] stop · [← →] step`. Footer
-  reads "step" not the mockup's "scrub" — single-move step is
-  what's wired; continuous scrub would need a key-held event
-  source. `ReplayOverlayPlugin` gains
-  `add_message::<UndoRequestEvent>()` defensively. 6 new tests
-  (2 hint pins + 4 keyboard scenarios) + 1 updated helper-pin
-  test; 1244 → 1250 total tests, 1249 passing.
 
-**Pre-existing flake noted (verified):**
+Open next-step menu (B-2 keyboard accelerator coverage +
-`daily_challenge_plugin::tests::
+accessibility + scrub UX are all complete):
-check_system_fires_warning_event_only_once_per_day` is
+1. **Move-log scroller / mini-tableau preview** — both need
-time-dependent — fails when wall-clock UTC is within 30
+   a much larger banner-height grow (effectively the takeover
-minutes of midnight (the daily-expiry warning window the test
+   container itself). Multi-session arcs that close B-2.
-asserts against). Verified pre-existing by stashing all
+   Mockup at `docs/ui-mockups/replay-overlay-mobile.html`.
-changes and re-running before commit — failure persisted. Same
+2. **Polish: notch label centering.** Bevy 0.18 lacks a clean
-shape as the `winnable_seed_search` flake from earlier in the
+   `translate-x: -50%` primitive so middle three labels sit
-session. Will pass deterministically when UTC isn't in the
+   slightly right-of-notch. Could use a child Text wrapper
-warning window. Not introduced by recent work.
+   with computed left-margin compensation. Tiny commit.
+3. **Polish: WIN MOVE marker HC bump.** Currently the marker
+   uses `STATE_SUCCESS` lime which stays visible under HC,
+   but a slight saturation / contrast bump under HC would
+   make the marker even more legible alongside the bumped
+   notches. Optional.
 
-Banner geometry is now mutable — every prior B-2 commit fit
+Recommended order: option 2 (notch label centering) is the
-inside fixed 60 px space, but the notch-labels commit
+smallest concrete next-step. Option 1 is the multi-session
-established the "grow the container, add a new flex-column
+arc that closes B-2 — natural place to start a fresh session.
-child" precedent and the keybind-footer commit applied it
-again. The next sub-pieces need significantly more vertical
-room and follow the same shape.
-
-Next finite step on B-2: keyboard accelerator coverage is now
-complete (`Space` / `Esc` / `←` / `→`). Remaining choices:
-1. **HC-mode coverage for the scrub-track / notch ticks /
-   WIN MOVE marker.** These render via `BackgroundColor` (not
-   `BorderColor`) so `HighContrastBorder` doesn't apply.
-   Pattern would mirror `radial_menu::radial_rim_outline` —
-   per-frame paint reading `Settings::high_contrast_mode`.
-   Small commit, accessibility-progressing.
-2. **Continuous scrub on key-held ← / →** instead of
-   single-move step. Needs a key-held event source (or
-   accumulator timer in the keyboard handler). Medium scope;
-   matches the mockup's `[← →] scrub` terminology.
-3. **Move-log scroller / mini-tableau preview** — both need a
-   much larger banner-height grow (effectively the takeover
-   container itself). Bigger arcs; the natural place to land
-   the layout reflow that turns the banner into a takeover.
-4. **Cut a v0.21.5 patch release** rolling up the four
-   post-cut commits (`fe68861`, `d322abf`, `1873b3f`,
-   `90e24d9`, `23902cd`, `e5c4f51`) under the through-line
-   "replay-overlay scrubbing affordances + accessibility."
-   Coherent narrative; six commits is a normal-sized patch
-   bundle for this project.
-
-Recommended order: option 4 (cut release) is a clean next
-boundary — six commits with a clear through-line is the right
-size to bundle. Option 1 (HC paint for decorative pieces) is
-the smallest next-feature commit if continuing past the cut.
 
 ## Open punch list
 
@@ -233,30 +136,24 @@ 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`. Quarter-mark
+  accelerator) shipped post-v0.21.3 in `fbe48ac`. v0.21.5
-  scrub notches (5 ticks at 0/25/50/75/100 %) shipped
+  bundled six more commits under "replay-overlay scrubbing
-  post-v0.21.4 in `fe68861` — first decoration step toward the
+  affordances + accessibility" — scrub notches + percentage
-  takeover layout. Percentage labels under each notch shipped
+  labels + keybind-hint footer + ESC and ← / → accelerators
-  post-v0.21.4 in `d322abf` — first **layout-changing** commit
+  + HC marker for the footer top border. Banner height grew
-  (banner 60 → 76 px). Keybind-hint footer shipped in `1873b3f`
+  60 → 76 → 92 px across two layout-changing commits in
-  (banner 76 → 92 px — vim-style mode line + `[SPACE]
+  v0.21.5; banner geometry is now mutable. Full per-commit
-  pause/resume`). ESC accelerator wiring (with cross-plugin
+  detail in `CHANGELOG.md` § [0.21.5]. Keyboard accelerator
-  gate in `pause_plugin::toggle_pause`) shipped in `90e24d9`.
+  coverage is complete. What still needs to land: HC-mode
-  HC-mode coverage for the footer's top border shipped in
+  coverage for the scrub-track / notches / WIN MOVE marker
-  `23902cd`. ← / → keyboard accelerators for paused stepping
+  (they render via `BackgroundColor` so the
-  shipped in `e5c4f51` (hooks the existing undo system for
+  `HighContrastBorder` marker doesn't apply — needs a
-  backwards step; footer extended to
+  settings-aware paint), continuous scrub on key-held ← / →
-  `[SPACE] pause/resume · [ESC] stop · [← →] step`). Banner
+  (vs single-step), then the bigger pieces — a move-log
-  geometry is mutable; keyboard accelerator coverage is
+  scroller and a mini-tableau preview — both screen-
-  complete. What still needs to land: HC-mode coverage for
+  takeover-only pieces that need a much larger banner height
-  the scrub-track / notches / WIN MOVE marker (they render
+  grow (effectively the takeover container itself).
-  via `BackgroundColor` so the `HighContrastBorder` marker
+  Multi-session.
-  doesn't apply — needs a settings-aware paint), continuous
-  scrub on key-held ← / → (vs single-step), then the bigger
-  pieces — a move-log scroller and a mini-tableau preview —
-  both screen-takeover-only pieces that need a much larger
-  banner height grow (effectively the takeover container
-  itself). Multi-session.
 - *Floating `MOVE N/M` chip above the focused card during
   playback — closed 2026-05-08 by `2fb2d63`.* World-space
   `Text2d` entity sibling to the banner overlay; uses the same
@@ -399,27 +296,25 @@ 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. v0.21.4 is tagged at 23ff62c (cut 2026-05-08, a
+Branch: master. v0.21.5 is tagged at a2432df (cut 2026-05-08, a
-patch release rolling up replay-scrubbing accessibility: WIN MOVE
+patch release rolling up replay-overlay scrubbing affordances +
-marker on the scrub bar, pause / resume / step playback controls
+accessibility: scrub-bar notches with percentage labels, keybind-
-with a Space keyboard accelerator, and the additive
+hint footer, ESC + ← / → keyboard accelerators, and HC-mode
-`Replay::win_move_index: Option<usize>` data field that makes the
+coverage for the footer top border). v0.21.4 stays at 23ff62c,
-marker possible). v0.21.3 stays at 3d92a91, v0.21.2 at f23df3b,
+v0.21.3 at 3d92a91, v0.21.2 at f23df3b, v0.21.1 at daa655a,
-v0.21.1 at daa655a, v0.21.0 at 04f9bf9. Working tree clean. See
+v0.21.0 at 04f9bf9. Working tree clean. See CHANGELOG.md §
-CHANGELOG.md § [0.21.4] for full detail.
+[0.21.5] for full detail.
 
-State: HEAD locally — see `git rev-parse HEAD`. Post-cut HEAD is
+State: HEAD locally — see `git rev-parse HEAD`. The cut commit
-`e5c4f51` (six carved-out commits on top of v0.21.4 — scrub-bar
+is a2432df; any post-cut docs edits ride on top of that.
-notches `fe68861`, notch labels `d322abf`, keybind-hint footer
+Workspace tests: 1250 total / 1249 passing / 1 pre-existing
-`1873b3f`, ESC accelerator + pause-modal gate `90e24d9`, HC
+time-dependent flake (`daily_challenge` warning, fails when UTC
-marker for footer border `23902cd`, ← / → keyboard accelerators
+is within 30 min of midnight; verified not introduced by recent
-`e5c4f51`). Workspace tests: 1250 total / 1249 passing / 1
+work). Clippy clean.
-pre-existing time-dependent flake (clock-near-midnight; verified
-not introduced by recent work). Clippy clean.
 
 READ FIRST (in order, before doing anything):
   1. SESSION_HANDOFF.md  — this file
-  2. CHANGELOG.md        — [0.21.4] section is the most recent cut
+  2. CHANGELOG.md        — [0.21.5] 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
@@ -440,33 +335,25 @@ DECISION TO ASK THE PLAYER FIRST:
      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 in v0.21.4: WIN MOVE
+     work. v0.21.4 shipped WIN MOVE marker, pause / resume /
-     marker (data field + UI) and pause / step / Space
+     step + Space accelerator, plus the floating-MOVE-chip
-     playback controls. The smaller floating-MOVE-chip piece
+     piece from v0.21.2 (`2fb2d63`). v0.21.5 shipped scrub
-     shipped in v0.21.2 (`2fb2d63`). Post-v0.21.4: scrub
+     notches + percentage labels + keybind-hint footer + ESC
-     notches `fe68861`, notch labels `d322abf` (banner
+     and ← / → accelerators + HC marker for the footer top
-     60 → 76 px), keybind-hint footer `1873b3f` (banner
+     border (six commits across CHANGELOG § [0.21.5]). Banner
-     76 → 92 px), ESC accelerator + cross-plugin gate
+     height grew 60 → 76 → 92 px across two layout-changing
-     `90e24d9`, HC-mode coverage for the footer top border
+     commits in v0.21.5; geometry is now mutable. Keyboard
-     `23902cd`, and ← / → keyboard accelerators for paused
+     accelerator coverage is complete. Natural next finite
-     stepping `e5c4f51` (hooks the game's undo system for
+     steps:
-     backwards step; footer extended to
+     1. **HC-mode coverage** for the scrub-track / notches /
-     `[SPACE] pause/resume · [ESC] stop · [← →] step`).
-     Keyboard accelerator coverage is complete. Natural next
-     finite steps:
-     1. **Cut a v0.21.5 patch release** rolling up the six
-        post-cut commits under "replay-overlay scrubbing
-        affordances + accessibility." Coherent narrative;
-        clean release boundary.
-     2. **HC-mode coverage** for the scrub-track / notches /
         WIN MOVE marker (render via `BackgroundColor` not
         `BorderColor`, so `HighContrastBorder` doesn't apply
         — needs a settings-aware paint, precedent
-        `radial_rim_outline`). Small commit.
+        `radial_rim_outline`). Smallest next commit.
-     3. **Continuous scrub on key-held ← / →** instead of
+     2. **Continuous scrub on key-held ← / →** instead of
         single-step. Needs a key-held event source. Matches
         the mockup's `[← →] scrub` terminology.
-     4. **Move-log scroller / mini-tableau preview** — both
+     3. **Move-log scroller / mini-tableau preview** — both
         need a much larger banner-height grow (effectively
         the takeover container itself). Multi-session arcs
         that close B-2.

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);