feat(engine): Phase F touch action bar — thumb-reach Undo/Draw/Hint + hold-to-repeat undo

Touch layout (USE_TOUCH_UI_LAYOUT) restructures the bottom action bar
to five buttons: an enlarged Undo / Draw / Hint trio (96x64px targets,
1.35x labels) between compact Menu and Pause. Draw is new — it fires
the same DrawRequestEvent as tapping the stock, so the most frequent
action no longer needs a reach to the top of a tall folded screen.
Help, Modes, and New Game leave the touch bar (they live in Menu ->
System, the Home grid, and Home's hero respectively). Desktop keeps
the seven-button bar unchanged (decision 5: touch-only).

Holding Undo now steps back repeatedly after a 0.45s delay (5.5/s),
each step through the normal request path so the scoring penalty
applies. New self-ambiguous DrawRequestWriters set keeps the ambiguity
gate at zero with the fourth DrawRequestEvent writer.

6 new hud_plugin tests; workspace suite + clippy green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_engine/src/hud_plugin/interaction.rs

@@ -30,6 +30,86 @@ pub(super) fn handle_undo_button(
     }
 }
 
+/// Seconds the Undo button must be continuously held before hold-to-repeat
+/// kicks in. Long enough that a normal tap (press + release inside one or
+/// two frames) never triggers a second undo.
+const UNDO_HOLD_INITIAL_DELAY_SECS: f32 = 0.45;
+
+/// Interval between repeated undos while the hold continues. ~5.5 undos/s —
+/// fast enough to unwind a long line, slow enough to release in time when
+/// the board reaches the state the player wants.
+const UNDO_HOLD_REPEAT_INTERVAL_SECS: f32 = 0.18;
+
+/// Hold-to-repeat undo (Phase F): while the Undo button stays pressed,
+/// fire additional [`UndoRequestEvent`]s after an initial delay, one per
+/// repeat interval. The plain tap path stays in [`handle_undo_button`]
+/// (its `Changed<Interaction>` filter fires exactly once per press);
+/// this system only adds events once the hold outlives the delay, so a
+/// tap never double-undoes.
+///
+/// Each repeat goes through the normal request queue — the scoring
+/// penalty and No-Undo-mode gating in the consumer apply to every step.
+pub(super) fn repeat_undo_on_hold(
+    time: Res<Time>,
+    buttons: Query<&Interaction, With<UndoButton>>,
+    mut state: ResMut<UndoHoldState>,
+    mut undo: MessageWriter<UndoRequestEvent>,
+) {
+    let held = buttons.iter().any(|i| *i == Interaction::Pressed);
+    if !held {
+        if state.held_secs != 0.0 {
+            state.held_secs = 0.0;
+        }
+        return;
+    }
+
+    let before = state.held_secs;
+    state.held_secs += time.delta_secs();
+    if undo_hold_crossed_fire_boundary(before, state.held_secs) {
+        undo.write(UndoRequestEvent);
+    }
+}
+
+/// `true` when a hold that lasted `before` seconds at the previous frame
+/// and `now` seconds this frame should fire a repeat undo: once when the
+/// hold first outlives the initial delay, then once per repeat-interval
+/// boundary. Pure so the timing contract is unit-testable without
+/// fighting `Time`.
+pub(super) fn undo_hold_crossed_fire_boundary(before: f32, now: f32) -> bool {
+    if now < UNDO_HOLD_INITIAL_DELAY_SECS {
+        return false;
+    }
+    if before < UNDO_HOLD_INITIAL_DELAY_SECS {
+        // Crossed the initial-delay threshold this frame — first repeat.
+        return true;
+    }
+    // Fire once each time the hold crosses another repeat-interval boundary.
+    let intervals_before =
+        ((before - UNDO_HOLD_INITIAL_DELAY_SECS) / UNDO_HOLD_REPEAT_INTERVAL_SECS).floor();
+    let intervals_now =
+        ((now - UNDO_HOLD_INITIAL_DELAY_SECS) / UNDO_HOLD_REPEAT_INTERVAL_SECS).floor();
+    intervals_now > intervals_before
+}
+
+/// Click on the touch action bar's Draw button — same
+/// [`DrawRequestEvent`] the stock-pile tap writes, so the consumer's
+/// rules (recycle, won-game rejection) apply identically. Skipped while
+/// paused, mirroring `handle_stock_click`'s guard.
+pub(super) fn handle_draw_button(
+    interaction_query: Query<&Interaction, (With<DrawButton>, Changed<Interaction>)>,
+    paused: Option<Res<PausedResource>>,
+    mut draw: MessageWriter<DrawRequestEvent>,
+) {
+    if paused.is_some_and(|p| p.0) {
+        return;
+    }
+    for interaction in &interaction_query {
+        if *interaction == Interaction::Pressed {
+            draw.write(DrawRequestEvent);
+        }
+    }
+}
+
 pub(super) fn handle_pause_button(
     interaction_query: Query<&Interaction, (With<PauseButton>, Changed<Interaction>)>,
     mut pause: MessageWriter<PauseRequestEvent>,