perf(ui): cancel the in-flight move preview when tiles move; debug cache-bust

Placing or recalling a tile fires the network preview; on a slow link the requests
piled up and an out-of-order response could overwrite the newest with a stale score.
Cancel the previous in-flight evaluate on each change — evaluate is non-mutating, so
aborting is safe (only submit_play and the debounced draft save persist), so only the
latest request runs and the newest result wins; the game also aborts it on unmount.
The abort threads an AbortSignal through the Connect exec (an intentional cancel does
not retry). The debug reset now also bypasses the browser HTTP cache on the next
dictionary load, so a "clear" forces a genuinely cold test — clearing IndexedDB alone
left the immutable blob served straight from the HTTP cache.

ui/src/components/DebugPanel.svelte

@@ -20,7 +20,7 @@
         const m = await import('../lib/dict');
         const list = await m.listCachedDicts();
         const cached = list.length ? list.map((d) => `${d.key}=${(d.bytes / 1024).toFixed(0)}KB`).join(' ') : 'none';
-        dictInfo = `dict breaker: ${m.dictLoadingDisabled() ? 'TRIPPED' : 'ok'}\ndicts cached: ${cached}`;
+        dictInfo = `local eval: ${m.LOCAL_EVAL_ENABLED ? 'on' : 'off'}  breaker: ${m.dictLoadingDisabled() ? 'TRIPPED' : 'ok'}\ndicts cached: ${cached}`;
       } catch {
         dictInfo = 'local eval: n/a';
       }

ui/src/game/Game.svelte

@@ -260,7 +260,7 @@
     // must never see the warm-up overlay, which would intercept the e2e's taps).
     if (import.meta.env.MODE !== 'mock') {
       void import('../lib/dict').then((m) => {
-        dict = m;
+        if (m.LOCAL_EVAL_ENABLED) dict = m;
       });
     }
   });

ui/src/lib/dict/config.ts

@@ -0,0 +1,6 @@
+// Feature flag for the on-device move preview (the local eval). Default on; append
+// `?nolocal` to the URL to force the network preview instead, for a side-by-side
+// check on the test contour. The network preview is always the fallback, so
+// disabling the flag only removes the acceleration, never the feature.
+export const LOCAL_EVAL_ENABLED =
+  typeof location === 'undefined' || !new URLSearchParams(location.search).has('nolocal');

ui/src/lib/dict/index.ts

@@ -5,3 +5,4 @@
 export { evaluateLocal } from './eval';
 export { getDawg, peekDawg, hasDawg, dictLoadingDisabled, noteDictMiss, clearDictInstances, bustDictHttpCache } from './loader';
 export { clearDictCache, listCachedDicts } from './store';
+export { LOCAL_EVAL_ENABLED } from './config';