fix(ui): abort a stalled dictionary download; trip the breaker on warm timeouts

On a slow link (EDGE) a dictionary download kept running in the background after the
warm-up gave up or the game was left, starving the channel — a new vs-AI game would
not open, and the breaker (which only counted fetch errors) never tripped, so the
warm-up overlay kept reappearing instead of settling to the network after a few
tries. Now:
- the warm-up passes an AbortSignal and aborts the download at its 5s cap, and the
  game aborts it on unmount (leaving the game), so a large download stops holding the
  channel — a subsequent action (creating a game) gets the bandwidth.
- the breaker counts warm-up misses (a load that failed OR hit the cap), not just
  fetch errors, so a persistently slow link trips it after 3 and the preview then
  goes straight to the network.

ui/src/game/Game.svelte

@@ -57,6 +57,9 @@
   let dict = $state<typeof import('../lib/dict') | null>(null);
   let dictWarming = $state(false);
   let warmStarted = false;
+  // Aborts the in-flight dictionary download (at the warm-up cap, or when leaving the game)
+  // so a large download does not keep starving the channel on a slow link.
+  let warmCtrl: AbortController | null = null;
   let zoomed = $state(false);
   let selected = $state<number | null>(null);
   let focus = $state<{ row: number; col: number } | null>(null);
@@ -594,6 +597,8 @@
     clearReorder();
   }
   onDestroy(() => {
+    // Leaving the game: abort a still-downloading dictionary so it stops holding the channel.
+    warmCtrl?.abort();
     window.removeEventListener('pointermove', onWinMove);
     window.removeEventListener('pointerup', onWinUp);
     window.removeEventListener('pointerdown', onExtraPointer);
@@ -673,16 +678,27 @@
     const v = view;
     if (!d || !v) return;
     if (d.hasDawg(v.game.variant, v.game.dictVersion) || d.dictLoadingDisabled()) return;
+    const ctrl = new AbortController();
+    warmCtrl = ctrl;
     let settled = false;
     // A short flash-guard: a disk-cached dictionary loads in a few ms, so only show the
     // overlay if the load has not settled by now — a cold (network) load always outlasts it.
     const grace = setTimeout(() => {
       if (!settled) dictWarming = true;
     }, 120);
-    await Promise.race([d.getDawg(v.game.variant, v.game.dictVersion), new Promise((r) => setTimeout(r, 5000))]);
+    const loaded = await Promise.race([
+      d.getDawg(v.game.variant, v.game.dictVersion, ctrl.signal),
+      new Promise<null>((r) => setTimeout(() => r(null), 5000)),
+    ]);
     settled = true;
     clearTimeout(grace);
     dictWarming = false;
+    if (!loaded) {
+      // Did not load within the cap: abort the download so it stops starving the channel this
+      // session, and count the miss toward the bad-connection breaker (3 -> stop warming).
+      ctrl.abort();
+      d.noteDictMiss();
+    }
   }
 
   let previewTimer: ReturnType<typeof setTimeout> | null = null;

ui/src/lib/client.ts

@@ -99,8 +99,9 @@ export interface GatewayClient {
 
   // --- dictionary (local move preview) ---
   /** Fetch the raw serialized dictionary blob for a (variant, version) pair. Session-gated;
-   *  lets the client validate and score a move locally instead of a network round trip. */
-  fetchDict(variant: Variant, version: string): Promise<ArrayBuffer>;
+   *  lets the client validate and score a move locally instead of a network round trip. The
+   *  optional signal aborts a stalled download so it stops holding the channel. */
+  fetchDict(variant: Variant, version: string, signal?: AbortSignal): Promise<ArrayBuffer>;
 
   // --- draft ---
   /** The player's server-persisted client-side composition (rack order + board tiles), so a

ui/src/lib/dict/index.ts

@@ -3,6 +3,6 @@
 // of the initial app bundle — it is a progressive enhancement over the network
 // preview, which remains the fallback.
 export { evaluateLocal } from './eval';
-export { getDawg, peekDawg, hasDawg, dictLoadingDisabled, clearDictInstances } from './loader';
+export { getDawg, peekDawg, hasDawg, dictLoadingDisabled, noteDictMiss, clearDictInstances } from './loader';
 export { clearDictCache, listCachedDicts } from './store';
 export { LOCAL_EVAL_ENABLED } from './config';

ui/src/lib/dict/loader.ts

@@ -16,16 +16,21 @@ const instances = new Map<string, Dawg>();
 // In-flight loads by key, so overlapping callers (prefetch + a game open) share one.
 const inflight = new Map<string, Promise<Dawg | null>>();
 
-// Bad-connection breaker: after a few dictionary downloads fail in a session, stop
-// attempting them so the player is not stuck watching the warm-up overlay when
-// switching games. It is session-scoped (in memory) — an app relaunch is a natural
-// retry, when the connection may have recovered. Cached dictionaries still load.
-const FAILURE_LIMIT = 3;
-let failures = 0;
+// Bad-connection breaker: after a few dictionaries fail to become available in a session
+// (a load that failed or a warm-up that hit its cap), stop attempting them so the player
+// is not stuck re-watching the warm-up overlay when switching games. Session-scoped (in
+// memory) — an app relaunch is a natural retry, when the connection may have recovered.
+// Cached dictionaries still load.
+const MISS_LIMIT = 3;
+let misses = 0;
 let dictDisabled = false;
 
-function noteFailure(): void {
-  if (!dictDisabled && ++failures >= FAILURE_LIMIT) dictDisabled = true;
+/**
+ * noteDictMiss records that a dictionary did not become available in time — a load that
+ * failed or a warm-up that hit its cap. After MISS_LIMIT in a session the breaker trips.
+ */
+export function noteDictMiss(): void {
+  if (!dictDisabled && ++misses >= MISS_LIMIT) dictDisabled = true;
 }
 
 /** dictLoadingDisabled reports whether the bad-connection breaker has tripped for this
@@ -40,18 +45,18 @@ export function dictLoadingDisabled(): boolean {
  * caller then previews over the network instead. Successful loads are cached in
  * memory and, when freshly fetched, in IndexedDB.
  */
-export function getDawg(variant: Variant, version: string): Promise<Dawg | null> {
+export function getDawg(variant: Variant, version: string, signal?: AbortSignal): Promise<Dawg | null> {
   const key = dictKey(variant, version);
   const have = instances.get(key);
   if (have) return Promise.resolve(have);
   const pending = inflight.get(key);
   if (pending) return pending;
-  const p = load(variant, version, key).finally(() => inflight.delete(key));
+  const p = load(variant, version, key, signal).finally(() => inflight.delete(key));
   inflight.set(key, p);
   return p;
 }
 
-async function load(variant: Variant, version: string, key: string): Promise<Dawg | null> {
+async function load(variant: Variant, version: string, key: string, signal?: AbortSignal): Promise<Dawg | null> {
   // Tier 1: the persistent cache.
   try {
     const cached = await idbGetDawg(key);
@@ -66,22 +71,22 @@ async function load(variant: Variant, version: string, key: string): Promise<Daw
     void idbDelDawg(key);
   }
 
-  // Tier 2: the session-gated download — gated by the bad-connection breaker.
+  // Tier 2: the session-gated download — gated by the bad-connection breaker. A caller's
+  // signal aborts it (the warm-up giving up at its cap, or the game being left) so a large
+  // download does not keep starving the channel on a slow link; the caller counts the miss.
   if (dictDisabled) return null;
   let buf: ArrayBuffer;
   try {
-    buf = await gateway.fetchDict(variant, version);
+    buf = await gateway.fetchDict(variant, version, signal);
   } catch {
-    noteFailure();
-    return null;
+    return null; // network error or aborted
   }
 
   let reader: Dawg;
   try {
     reader = new Dawg(new Uint8Array(buf));
   } catch {
-    noteFailure();
-    return null; // a corrupt blob — do not cache it
+    return null; // not a dawg — do not cache it
   }
   instances.set(key, reader);
   void idbPutDawg(key, buf);
@@ -114,6 +119,6 @@ export function peekDawg(variant: Variant, version: string): Dawg | null {
  */
 export function clearDictInstances(): void {
   instances.clear();
-  failures = 0;
+  misses = 0;
   dictDisabled = false;
 }

ui/src/lib/mock/client.ts

@@ -161,7 +161,7 @@ export class MockGateway implements GatewayClient {
     // The mock never blocks; the blocked screen is driven directly via the mock-mode __block seam.
     return { blocked: false, permanent: false, until: '', reason: '' };
   }
-  async fetchDict(_variant: Variant, _version: string): Promise<ArrayBuffer> {
+  async fetchDict(_variant: Variant, _version: string, _signal?: AbortSignal): Promise<ArrayBuffer> {
     // No local dictionary in mock mode; the caller falls back to the mock evaluate.
     throw new Error('fetchDict unsupported in mock');
   }

ui/src/lib/transport.ts

@@ -62,14 +62,16 @@ export function createTransport(baseUrl: string): GatewayClient {
       token = t;
     },
 
-    async fetchDict(variant, version) {
+    async fetchDict(variant, version, signal) {
       if (!token) throw new Error('fetchDict: no session');
       // Low priority so the browser schedules the (large) dictionary behind the game's own
       // requests — the move eval, state and live events — on a slow link (EDGE). Ignored
-      // where the Priority Hints API is unsupported (iOS WebKit), which is harmless.
+      // where the Priority Hints API is unsupported (iOS WebKit), which is harmless. The
+      // signal lets the caller abort a stalled download so it stops holding the channel.
       const res = await fetch(`${origin}/dict/${encodeURIComponent(variant)}/${encodeURIComponent(version)}`, {
         headers: { authorization: `Bearer ${token}` },
         priority: 'low',
+        signal,
       } as RequestInit);
       if (!res.ok) throw new Error(`fetchDict ${variant}/${version}: HTTP ${res.status}`);
       return res.arrayBuffer();