feat(ui delta upload): user can change oxi.UPLOAD_BATCH_BYTES

```
oxi.UPLOAD_BATCH_BYTES // get current value
oxi.UPLOAD_BATCH_BYTES=1024*1024 // change values
```

values are stored in localstorage, default is 8*1024*1024

frontend/src/hooks.client.ts

@@ -10,38 +10,75 @@ import { session } from '$lib/stores/session.svelte';
 import { seedNonceFromCookie } from '$lib/auth/dpop-proof';
 
 // DevTools shortcut: expose a small `oxi.*` helper on window so users
-// can toggle log levels from the browser console without needing to
-// import anything. Namespaces used today: `oxi:upload` (delta + direct
+// can toggle log levels and knobs from the browser console without
+// needing to import anything.
+//
+// Log levels — namespaces used today: `oxi:upload` (delta + direct
 // upload pipeline). Levels: 'trace' | 'debug' | 'info' | 'warn' | 'error' | 'silent'.
 // Choices persist to `localStorage['loglevel:<namespace>']` via loglevel.
 //
-// Usage:
 //   oxi.setLogLevel('oxi:upload', 'debug')    // deep dive
 //   oxi.setLogLevel('oxi:upload', 'warn')     // quiet
 //   oxi.log.setLevel('debug')                  // everything to debug
+//
+// Delta-upload batch size — bytes per PUT to `/api/files/delta/chunks`.
+// Default 8 MiB. Behind proxies with tight per-request timeouts
+// (Cloudflare Tunnel: 100 s absolute), lower this so each PUT completes
+// within the window on a slow uplink:
+//
+//   oxi.UPLOAD_BATCH_BYTES = 1024 * 1024      // 1 MiB per PUT
+//
+// Persists to `localStorage['oxi:upload:batchBytes']`. Read on every
+// upload — set once from the console, refresh not required.
+const BATCH_BYTES_KEY = 'oxi:upload:batchBytes';
+const BATCH_BYTES_DEFAULT = 8 * 1024 * 1024;
+
+function readBatchBytes(): number {
+	try {
+		if (typeof localStorage === 'undefined') return BATCH_BYTES_DEFAULT;
+		const raw = localStorage.getItem(BATCH_BYTES_KEY);
+		if (!raw) return BATCH_BYTES_DEFAULT;
+		const n = Number(raw);
+		return Number.isFinite(n) && n > 0 ? n : BATCH_BYTES_DEFAULT;
+	} catch {
+		return BATCH_BYTES_DEFAULT;
+	}
+}
+
+function writeBatchBytes(n: number): void {
+	if (typeof localStorage === 'undefined') return;
+	try {
+		if (n === BATCH_BYTES_DEFAULT) localStorage.removeItem(BATCH_BYTES_KEY);
+		else localStorage.setItem(BATCH_BYTES_KEY, String(n));
+	} catch {
+		/* quota / disabled — best-effort */
+	}
+}
+
 declare global {
 	interface Window {
 		oxi?: {
 			log: typeof log;
 			setLogLevel: (namespace: string, level: log.LogLevelDesc) => string;
 			listLogLevels: () => Record<string, string>;
+			UPLOAD_BATCH_BYTES: number;
 		};
 	}
 }
 
 export async function init(): Promise<void> {
 	if (typeof window !== 'undefined') {
-		window.oxi = {
+		const helpers = {
 			log,
 			// Return a confirmation string so the DevTools echo is a
 			// useful "worked → new level" signal instead of `undefined`.
-			setLogLevel(namespace, level) {
+			setLogLevel(namespace: string, level: log.LogLevelDesc): string {
 				log.getLogger(namespace).setLevel(level);
 				return `${namespace} → ${level}`;
 			},
 			// Enumerate the levels loglevel has persisted so users can see
 			// what's currently set without opening the Application tab.
-			listLogLevels() {
+			listLogLevels(): Record<string, string> {
 				const out: Record<string, string> = {};
 				if (typeof localStorage === 'undefined') return out;
 				for (let i = 0; i < localStorage.length; i++) {
@@ -53,6 +90,17 @@ export async function init(): Promise<void> {
 				return out;
 			}
 		};
+		// UPLOAD_BATCH_BYTES: getter reads live from localStorage so any
+		// tab / component pulling `window.oxi.UPLOAD_BATCH_BYTES` sees the
+		// current value; setter persists so the choice survives reload
+		// (mirrors loglevel's persistence pattern).
+		Object.defineProperty(helpers, 'UPLOAD_BATCH_BYTES', {
+			get: readBatchBytes,
+			set: writeBatchBytes,
+			enumerable: true,
+			configurable: true
+		});
+		window.oxi = helpers as Window['oxi'];
 	}
 
 	setSessionExpiredHandler(() => {

frontend/src/lib/api/endpoints/deltaUpload.ts

@@ -252,7 +252,20 @@ export function tryDeltaUpload(
 			settle(null);
 		};
 
-		worker.postMessage({ file, folderId, name: file.name, csrfToken: getCsrfToken() || '' });
+		// Runtime-tunable batch size (`window.oxi.UPLOAD_BATCH_BYTES`,
+		// persisted to localStorage). Undefined = worker uses its own
+		// default (8 MiB). Behind Cloudflare Tunnel or other proxies
+		// with tight per-request timeouts, users can lower it via
+		// `oxi.UPLOAD_BATCH_BYTES = 1024 * 1024` so each PUT completes
+		// well inside the proxy's 100 s window on a slow uplink.
+		const uploadBatchBytes = window.oxi?.UPLOAD_BATCH_BYTES;
+		worker.postMessage({
+			file,
+			folderId,
+			name: file.name,
+			csrfToken: getCsrfToken() || '',
+			uploadBatchBytes
+		});
 	});
 }
 

frontend/static/workers/deltaWorker.js

@@ -28,8 +28,13 @@ const WASM_GLUE_URL = '/vendors/hash-wasm/oxicloud_hash_wasm.js';
 const SLICE_BYTES = 8 * 1024 * 1024;
 /** Negotiate after this many freshly hashed chunks (~64 MiB of content). */
 const NEGOTIATE_BATCH = 256;
-/** Group missing chunks into PUT bodies of at most this many bytes. */
-const UPLOAD_BATCH_BYTES = 8 * 1024 * 1024;
+/** Default target size of a PUT body (grouping multiple chunk frames).
+ *  The orchestrator may override this per-upload via the init message's
+ *  `uploadBatchBytes` field, sourced from `window.oxi.UPLOAD_BATCH_BYTES`.
+ *  Lowering it (say to 1 MiB) helps clients behind proxies with tight
+ *  per-request timeouts (Cloudflare Tunnel: 100 s absolute) at the cost
+ *  of more requests per file. */
+const UPLOAD_BATCH_BYTES_DEFAULT = 8 * 1024 * 1024;
 /** Reclaim consumed queue slots periodically. A head cursor makes dequeue O(1);
  *  compaction bounds the backing array when hashing stays ahead of the network. */
 const UPLOAD_QUEUE_COMPACT_AT = 4096;
@@ -63,7 +68,13 @@ async function loadWasm() {
 }
 
 workerScope.onmessage = async (event) => {
-    const { file, folderId, name, csrfToken } = /** @type {{ file: File, folderId: string, name: string, csrfToken: string }} */ (event.data);
+    const { file, folderId, name, csrfToken, uploadBatchBytes } = /** @type {{ file: File, folderId: string, name: string, csrfToken: string, uploadBatchBytes?: number }} */ (event.data);
+    // Per-upload override sourced from `window.oxi.UPLOAD_BATCH_BYTES`
+    // in the main thread. Falls back to the module default (8 MiB).
+    const uploadBatchBytesEff =
+        typeof uploadBatchBytes === 'number' && uploadBatchBytes > 0
+            ? uploadBatchBytes
+            : UPLOAD_BATCH_BYTES_DEFAULT;
 
     /**
      * Forward a log line to the main-thread orchestrator, which routes it
@@ -158,11 +169,11 @@ workerScope.onmessage = async (event) => {
 
     const uploadLoop = async () => {
         while (!failed) {
-            // Take up to UPLOAD_BATCH_BYTES from the queue.
+            // Take up to the effective per-PUT byte cap from the queue.
             /** @type {WorkerChunk[]} */
             const batch = [];
             let bytes = 0;
-            while (uploadHead < uploadQueue.length && bytes < UPLOAD_BATCH_BYTES) {
+            while (uploadHead < uploadQueue.length && bytes < uploadBatchBytesEff) {
                 const c = /** @type {WorkerChunk} */ (uploadQueue[uploadHead]);
                 uploadQueue[uploadHead] = undefined;
                 uploadHead++;