refactor(engine): ambiguity burn-down batch 4 — zero ambiguities, gate enforced

Clears the final 47 pairs and turns the ratchet into a hard gate
(AMBIGUITY_BASELINE = 0, assert_eq):

- HudButtons: the 14 HUD button/popover handlers run as one chain,
  before ui_focus::FocusKeys — Esc/keyboard consumption order is now
  defined (restore prompt → buttons/popovers → focus navigation →
  settings toggle) instead of scheduler-dependent.
- HUD text updaters (update_hud, update_selection_hud,
  update_won_previously) chained, in UiTextFx, after the new
  AutoComplete set (update_hud reads AutoCompleteState).
- restore_hud_on_modal → apply_hud_visibility chained before
  UpdateOnResize: HudVisibility writes, application, and the layout
  read happen in a fixed order.
- New writer sets UndoRequestWriters / InfoToastWriters (same
  self-ambiguous pattern as NewGameRequestWriters).
- Logic-before-paint: check_no_moves and the AutoComplete chain order
  before BoardVisuals; SettingsMutation after UpdateOnResize.
- MarkerVisuals set wraps the table painter chain; chrome fx declare
  disjointness from it.
- update_hud_typography after BoardVisuals; avatar/settings-toggle
  interaction handlers declared disjoint from HudButtons.

302 → 198 → 171 → 47 → 0 in four batches, one day. New systems now
fail CI unless they declare their ordering or their disjointness.

Closes #143

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

solitaire_engine/src/schedule_checks.rs

@@ -32,13 +32,14 @@ mod tests {
     use crate::ui_focus::UiFocusPlugin;
     use crate::ui_modal::UiModalPlugin;
 
-    /// Legacy ambiguity backlog measured 2026-07-06 (issue #143). This
-    /// number may only decrease. If your change trips this assertion you
-    /// have added a pair of systems with conflicting data access and no
-    /// ordering edge — add `.before`/`.after` (order matters) or
-    /// `.ambiguous_with` (provably order-independent) at the registration
-    /// site. When triage lowers the real count, lower this constant too.
-    const AMBIGUITY_BASELINE: usize = 47;
+    /// The backlog (302 pairs on 2026-07-06) was burned down to ZERO the
+    /// same day (#143, PRs #146–#149) — this is now a hard gate. If your
+    /// change trips this assertion you have added a pair of systems with
+    /// conflicting data access and no ordering edge: add `.before`/`.after`
+    /// where order matters, or `.ambiguous_with` the relevant domain set
+    /// (BoardVisuals, MarkerVisuals, UiTextFx, HudButtons, writer sets)
+    /// where it provably does not. Do not raise this constant.
+    const AMBIGUITY_BASELINE: usize = 0;
 
     fn cluster_app() -> App {
         let mut app = App::new();
@@ -96,10 +97,12 @@ mod tests {
             }
         };
 
-        assert!(
-            count <= AMBIGUITY_BASELINE,
-            "system-order ambiguities grew: {count} > baseline {AMBIGUITY_BASELINE}. \
-             Add .before/.after or .ambiguous_with at the new registration site.",
+        assert_eq!(
+            count, AMBIGUITY_BASELINE,
+            "system-order ambiguities changed from the enforced baseline. \
+             Add .before/.after or .ambiguous_with at the new registration site \
+             (or, if the count legitimately dropped below a nonzero baseline, \
+             lower AMBIGUITY_BASELINE).",
         );
     }
 }