studio chat: harden autoload singleflight + abort handling

Three follow-up fixes from the PR review pass:

- Follower callers (sharing an in-flight cascade) now race their own
  abortSignal against the leader's promise, so a cancelled stream is
  no longer blocked on the leader's lifecycle.
- Pre-aborted entry into autoLoadSmallestModel bails before the
  "Loading a model..." toast fires, avoiding a flash for abort-then-
  send sequences.
- Fallback-gate abort path now returns blockedByTrustRemoteCode:false
  (matching the early-abort blocks at the loop bodies). Avoids
  surfacing "Enable custom code" when the real outcome was an abort.

studio/frontend/src/features/chat/api/chat-adapter.ts

@@ -439,11 +439,69 @@ function waitForModelReady(abortSignal?: AbortSignal): Promise<void> {
  */
 // Cap cascade so broken cached repos can't spam /api/inference/load.
 const MAX_AUTO_LOAD_ATTEMPTS = 3;
+// /validate is cheaper but a long trust-blocked cache still produces one POST
+// per repo; cap that path separately so the cascade is fully bounded.
+const MAX_AUTO_VALIDATE_ATTEMPTS = 10;
 
-async function autoLoadSmallestModel(): Promise<{
+// Singleflight handle: concurrent sends arriving while a cascade is in
+// flight share its result instead of fanning out another /load budget.
+let autoLoadInflight: Promise<{
+  loaded: boolean;
+  blockedByTrustRemoteCode: boolean;
+}> | null = null;
+
+async function autoLoadSmallestModel(abortSignal?: AbortSignal): Promise<{
   loaded: boolean;
   blockedByTrustRemoteCode: boolean;
 }> {
+  // Pre-aborted callers bail before even creating a toast.
+  if (abortSignal?.aborted) {
+    return { loaded: false, blockedByTrustRemoteCode: false };
+  }
+  // Followers share the leader's cascade result but race against their own
+  // abortSignal so a cancelled stream isn't blocked on the leader.
+  if (autoLoadInflight) return awaitWithAbort(autoLoadInflight, abortSignal);
+  const work = runAutoLoadCascade(abortSignal);
+  autoLoadInflight = work;
+  try {
+    return await work;
+  } finally {
+    autoLoadInflight = null;
+  }
+}
+
+function awaitWithAbort(
+  work: Promise<{ loaded: boolean; blockedByTrustRemoteCode: boolean }>,
+  signal?: AbortSignal,
+): Promise<{ loaded: boolean; blockedByTrustRemoteCode: boolean }> {
+  if (!signal) return work;
+  if (signal.aborted) {
+    return Promise.resolve({ loaded: false, blockedByTrustRemoteCode: false });
+  }
+  return new Promise((resolve, reject) => {
+    const onAbort = () =>
+      resolve({ loaded: false, blockedByTrustRemoteCode: false });
+    signal.addEventListener("abort", onAbort, { once: true });
+    work.then(
+      (value) => {
+        signal.removeEventListener("abort", onAbort);
+        resolve(value);
+      },
+      (err) => {
+        signal.removeEventListener("abort", onAbort);
+        reject(err);
+      },
+    );
+  });
+}
+
+async function runAutoLoadCascade(abortSignal?: AbortSignal): Promise<{
+  loaded: boolean;
+  blockedByTrustRemoteCode: boolean;
+}> {
+  if (abortSignal?.aborted) {
+    return { loaded: false, blockedByTrustRemoteCode: false };
+  }
   const store = useChatRuntimeStore.getState();
   const hfToken = store.hfToken || null;
   const trustRemoteCode = store.params.trustRemoteCode ?? false;
@@ -455,6 +513,7 @@ async function autoLoadSmallestModel(): Promise<{
   let blockedByTrustRemoteCode = false;
   let hadNonTrustFailure = false;
   let loadAttempts = 0;
+  let validateAttempts = 0;
 
   async function canAutoLoad(payload: {
     model_path: string;
@@ -462,6 +521,8 @@ async function autoLoadSmallestModel(): Promise<{
     is_lora: boolean;
     gguf_variant?: string | null;
   }): Promise<boolean> {
+    if (validateAttempts >= MAX_AUTO_VALIDATE_ATTEMPTS) return false;
+    validateAttempts += 1;
     const validation = await validateModel({
       ...payload,
       hf_token: hfToken,
@@ -480,11 +541,17 @@ async function autoLoadSmallestModel(): Promise<{
       listCachedModels().catch(() => []),
     ]);
 
+    if (abortSignal?.aborted) {
+      toast.dismiss(toastId);
+      return { loaded: false, blockedByTrustRemoteCode: false };
+    }
+
     // Try GGUF first: pick the repo with the smallest total size,
     // then pick its smallest downloaded variant.
     if (ggufRepos.length > 0) {
       const sorted = [...ggufRepos].sort((a, b) => a.size_bytes - b.size_bytes);
       for (const repo of sorted) {
+        if (abortSignal?.aborted) break;
         if (loadAttempts >= MAX_AUTO_LOAD_ATTEMPTS) break;
         try {
           const variants = await listGgufVariants(repo.repo_id);
@@ -566,6 +633,7 @@ async function autoLoadSmallestModel(): Promise<{
     if (modelRepos.length > 0) {
       const sorted = [...modelRepos].sort((a, b) => a.size_bytes - b.size_bytes);
       for (const repo of sorted) {
+        if (abortSignal?.aborted) break;
         if (loadAttempts >= MAX_AUTO_LOAD_ATTEMPTS) break;
         try {
           if (
@@ -624,6 +692,10 @@ async function autoLoadSmallestModel(): Promise<{
       }
     }
 
+    if (abortSignal?.aborted) {
+      toast.dismiss(toastId);
+      return { loaded: false, blockedByTrustRemoteCode: false };
+    }
     // Cap also gates the default download so the total /api/inference/load
     // budget across cached + fallback is MAX_AUTO_LOAD_ATTEMPTS, not +1.
     if (loadAttempts >= MAX_AUTO_LOAD_ATTEMPTS) {
@@ -736,7 +808,7 @@ export function createOpenAIStreamAdapter(): ChatModelAdapter {
       if (!useChatRuntimeStore.getState().params.checkpoint) {
         // Auto-load the smallest downloaded model
         const { loaded, blockedByTrustRemoteCode } =
-          await autoLoadSmallestModel();
+          await autoLoadSmallestModel(abortSignal);
         if (!loaded) {
           toast.error(
             blockedByTrustRemoteCode

unsloth_cli/commands/studio.py

@@ -1315,7 +1315,7 @@ def _release_self_exe_lock_windows() -> None:
         os.replace(exe, stale)
     except OSError as e:
         # Not fatal; setup.ps1 retries from a sibling process.
-        print(f"[update] could not rename {exe.name} -> {stale.name}: {e}")
+        typer.echo(f"[update] could not rename {exe.name} -> {stale.name}: {e}")
 
 
 def _restore_self_exe_lock_windows() -> None:
@@ -1341,7 +1341,7 @@ def _restore_self_exe_lock_windows() -> None:
     try:
         os.replace(stale, exe)
     except OSError as e:
-        print(f"[update] could not restore {stale.name} -> {exe.name}: {e}")
+        typer.echo(f"[update] could not restore {stale.name} -> {exe.name}: {e}")
 
 
 def _cleanup_self_exe_lock_windows() -> None: