diff --git a/apps/desktop/electron/hardening.test.ts b/apps/desktop/electron/hardening.test.ts
index 1a5852f720af..4b41962e0cdb 100644
--- a/apps/desktop/electron/hardening.test.ts
+++ b/apps/desktop/electron/hardening.test.ts
@@ -7,6 +7,9 @@ import { pathToFileURL } from 'node:url'
 import { test } from 'vitest'
 
 import {
+  clampDataUrlReadMaxMb,
+  DATA_URL_READ_DEFAULT_MAX_MB,
+  dataUrlReadMaxBytesFromMb,
   DEFAULT_FETCH_TIMEOUT_MS,
   encryptDesktopSecret,
   resolveDirectoryForIpc,
@@ -24,6 +27,14 @@ async function rejectsWithCode(promise, code: string) {
   })
 }
 
+test('clampDataUrlReadMaxMb defaults and bounds the attach size preference', () => {
+  assert.equal(clampDataUrlReadMaxMb(undefined), DATA_URL_READ_DEFAULT_MAX_MB)
+  assert.equal(clampDataUrlReadMaxMb(0), 1)
+  assert.equal(clampDataUrlReadMaxMb(256), 256)
+  assert.equal(clampDataUrlReadMaxMb(99999), 4096)
+  assert.equal(dataUrlReadMaxBytesFromMb(16), 16 * 1024 * 1024)
+})
+
 test('resolveTimeoutMs falls back to defaults and accepts overrides', () => {
   assert.equal(resolveTimeoutMs(undefined), DEFAULT_FETCH_TIMEOUT_MS)
   assert.equal(resolveTimeoutMs(0), DEFAULT_FETCH_TIMEOUT_MS)
diff --git a/apps/desktop/electron/hardening.ts b/apps/desktop/electron/hardening.ts
index 2d6b53310018..de15a5dca5e3 100644
--- a/apps/desktop/electron/hardening.ts
+++ b/apps/desktop/electron/hardening.ts
@@ -4,9 +4,30 @@ import path from 'node:path'
 import { fileURLToPath } from 'node:url'
 
 const DEFAULT_FETCH_TIMEOUT_MS = 15_000
-const DATA_URL_READ_MAX_BYTES = 16 * 1024 * 1024
+// Default / floor / ceiling for Desktop's data-URL file load (composer attach,
+// image preview, etc.). The whole file is base64-buffered in main, so this is
+// a memory guard — not a model limit. Settings → Chat takes a free-form MB
+// value; 16 MB ships as default. The ceiling is only a typo guard (very large
+// values can OOM / crash the app).
+const DATA_URL_READ_DEFAULT_MAX_MB = 16
+const DATA_URL_READ_MIN_MAX_MB = 1
+const DATA_URL_READ_MAX_MAX_MB = 4096
 const TEXT_PREVIEW_SOURCE_MAX_BYTES = 64 * 1024 * 1024
 
+function clampDataUrlReadMaxMb(value) {
+  const parsed = Number(value)
+
+  if (!Number.isFinite(parsed)) {
+    return DATA_URL_READ_DEFAULT_MAX_MB
+  }
+
+  return Math.min(DATA_URL_READ_MAX_MAX_MB, Math.max(DATA_URL_READ_MIN_MAX_MB, Math.round(parsed)))
+}
+
+function dataUrlReadMaxBytesFromMb(maxMb) {
+  return clampDataUrlReadMaxMb(maxMb) * 1024 * 1024
+}
+
 const SAFE_ENV_SUFFIXES = new Set(['dist', 'example', 'sample', 'template'])
 const SENSITIVE_EXTENSIONS = new Set(['.kdbx', '.p12', '.pem', '.pfx'])
 
@@ -304,7 +325,11 @@ async function resolveReadableFileForIpc(
 }
 
 export {
-  DATA_URL_READ_MAX_BYTES,
+  clampDataUrlReadMaxMb,
+  DATA_URL_READ_DEFAULT_MAX_MB,
+  DATA_URL_READ_MAX_MAX_MB,
+  DATA_URL_READ_MIN_MAX_MB,
+  dataUrlReadMaxBytesFromMb,
   DEFAULT_FETCH_TIMEOUT_MS,
   encryptDesktopSecret,
   rejectUnsafePathSyntax,
diff --git a/apps/desktop/electron/main.ts b/apps/desktop/electron/main.ts
index 3dc41b784982..dfb4747f0392 100644
--- a/apps/desktop/electron/main.ts
+++ b/apps/desktop/electron/main.ts
@@ -115,7 +115,9 @@ import {
   switchBranch
 } from './git-worktree-ops'
 import {
-  DATA_URL_READ_MAX_BYTES,
+  clampDataUrlReadMaxMb,
+  DATA_URL_READ_DEFAULT_MAX_MB,
+  dataUrlReadMaxBytesFromMb,
   DEFAULT_FETCH_TIMEOUT_MS,
   encryptDesktopSecret as encryptDesktopSecretStrict,
   resolveReadableFileForIpc,
@@ -960,7 +962,7 @@ app.setAboutPanelOptions({
 
 // Custom scheme for streaming local media (video/audio) into the renderer.
 // Reading large media through `readFileDataUrl` failed: it base64-loads the
-// whole file into memory and is hard-capped at DATA_URL_READ_MAX_BYTES (16 MB),
+// whole file into memory and is hard-capped (default 16 MB, Settings → Chat),
 // so any non-trivial video silently refused to load. Streaming via a protocol
 // handler removes the size cap and gives the <video> element seekable,
 // range-aware playback. Must be registered before the app is ready.
@@ -10052,9 +10054,56 @@ ipcMain.handle('hermes:notify', (_event, payload) => {
   return true
 })
 
+// Data-URL file load cap (composer attach + local previews). Main owns the
+// persisted MB value so every IPC read honours Settings → Chat without the
+// renderer having to pass maxBytes on each call. Default is 16 MB; clamp
+// lives in hardening.ts.
+const DATA_URL_READ_MAX_CONFIG_PATH = path.join(app.getPath('userData'), 'data-url-read-max.json')
+
+function readPersistedDataUrlReadMaxMb() {
+  try {
+    return clampDataUrlReadMaxMb(JSON.parse(fs.readFileSync(DATA_URL_READ_MAX_CONFIG_PATH, 'utf8')).maxMb)
+  } catch {
+    return DATA_URL_READ_DEFAULT_MAX_MB
+  }
+}
+
+let dataUrlReadMaxMb = readPersistedDataUrlReadMaxMb()
+
+function persistDataUrlReadMaxMb(maxMb) {
+  const next = clampDataUrlReadMaxMb(maxMb)
+  dataUrlReadMaxMb = next
+
+  try {
+    fs.mkdirSync(path.dirname(DATA_URL_READ_MAX_CONFIG_PATH), { recursive: true })
+    fs.writeFileSync(DATA_URL_READ_MAX_CONFIG_PATH, JSON.stringify({ maxMb: next }, null, 2), 'utf8')
+  } catch (error) {
+    rememberLog(`[data-url-read-max] write failed: ${error.message}`)
+  }
+
+  return next
+}
+
+ipcMain.handle('hermes:data-url-read-max:get', () => ({
+  maxMb: dataUrlReadMaxMb,
+  // Keep the default bytes constant visible for tests / diagnostics.
+  defaultMaxMb: DATA_URL_READ_DEFAULT_MAX_MB,
+  maxBytes: dataUrlReadMaxBytesFromMb(dataUrlReadMaxMb)
+}))
+
+ipcMain.handle('hermes:data-url-read-max:set', (_event, maxMb) => {
+  const next = persistDataUrlReadMaxMb(maxMb)
+
+  return {
+    maxMb: next,
+    defaultMaxMb: DATA_URL_READ_DEFAULT_MAX_MB,
+    maxBytes: dataUrlReadMaxBytesFromMb(next)
+  }
+})
+
 ipcMain.handle('hermes:readFileDataUrl', async (_event, filePath) => {
   const { resolvedPath } = await resolveReadableFileForIpc(filePath, {
-    maxBytes: DATA_URL_READ_MAX_BYTES,
+    maxBytes: dataUrlReadMaxBytesFromMb(dataUrlReadMaxMb),
     purpose: 'File preview'
   })
 
diff --git a/apps/desktop/electron/preload.ts b/apps/desktop/electron/preload.ts
index 059a03986afe..815f048359b3 100644
--- a/apps/desktop/electron/preload.ts
+++ b/apps/desktop/electron/preload.ts
@@ -98,6 +98,10 @@ contextBridge.exposeInMainWorld('hermesDesktop', {
   notify: payload => ipcRenderer.invoke('hermes:notify', payload),
   requestMicrophoneAccess: () => ipcRenderer.invoke('hermes:requestMicrophoneAccess'),
   readFileDataUrl: filePath => ipcRenderer.invoke('hermes:readFileDataUrl', filePath),
+  dataUrlReadMax: {
+    get: () => ipcRenderer.invoke('hermes:data-url-read-max:get'),
+    set: maxMb => ipcRenderer.invoke('hermes:data-url-read-max:set', maxMb)
+  },
   readFileText: filePath => ipcRenderer.invoke('hermes:readFileText', filePath),
   selectPaths: options => ipcRenderer.invoke('hermes:selectPaths', options),
   writeClipboard: text => ipcRenderer.invoke('hermes:writeClipboard', text),
diff --git a/apps/desktop/src/app/session/hooks/use-prompt-actions/index.test.tsx b/apps/desktop/src/app/session/hooks/use-prompt-actions/index.test.tsx
index 6bf51c1e0fc7..c1660530a035 100644
--- a/apps/desktop/src/app/session/hooks/use-prompt-actions/index.test.tsx
+++ b/apps/desktop/src/app/session/hooks/use-prompt-actions/index.test.tsx
@@ -3844,7 +3844,7 @@ describe('uploadComposerAttachment remote read failures', () => {
 
   it('turns the raw 16MB IPC cap error into a friendly remote-gateway message', async () => {
     // electron/hardening.ts rejects the readFileDataUrl IPC with this exact
-    // shape when a file exceeds DATA_URL_READ_MAX_BYTES.
+    // shape when a file exceeds the configured data-URL read cap.
     Object.defineProperty(window, 'hermesDesktop', {
       configurable: true,
       value: {
diff --git a/apps/desktop/src/app/session/hooks/use-prompt-actions/utils.ts b/apps/desktop/src/app/session/hooks/use-prompt-actions/utils.ts
index a2ec14eb2a5a..d586448aee91 100644
--- a/apps/desktop/src/app/session/hooks/use-prompt-actions/utils.ts
+++ b/apps/desktop/src/app/session/hooks/use-prompt-actions/utils.ts
@@ -168,7 +168,7 @@ export async function readFileDataUrlForAttach(filePath: string): Promise<string
 }
 
 // The readFileDataUrl IPC base64-loads the whole file into memory and is
-// hard-capped (DATA_URL_READ_MAX_BYTES, 16 MB) in electron/hardening.ts, which
+// hard-capped in the main process (default 16 MB; Settings → Chat), which
 // rejects with a raw "file is too large (N bytes; limit M bytes)" string. In
 // remote mode every attachment's bytes go through that read, so a big file
 // surfaces that internal message verbatim in the failure toast. Translate it
diff --git a/apps/desktop/src/app/settings/config-settings.tsx b/apps/desktop/src/app/settings/config-settings.tsx
index 38747792732d..b3ee279a79d2 100644
--- a/apps/desktop/src/app/settings/config-settings.tsx
+++ b/apps/desktop/src/app/settings/config-settings.tsx
@@ -5,8 +5,19 @@ import { useEffect, useMemo, useRef, useState } from 'react'
 import { useSearchParams } from 'react-router-dom'
 
 import { Button } from '@/components/ui/button'
+import { Input } from '@/components/ui/input'
 import { getElevenLabsVoices, getHermesConfigSchema, saveHermesConfig } from '@/hermes'
 import { useI18n } from '@/i18n'
+import { triggerHaptic } from '@/lib/haptics'
+import {
+  $dataUrlReadMaxMb,
+  clampDataUrlReadMaxMb,
+  DATA_URL_READ_DEFAULT_MAX_MB,
+  DATA_URL_READ_MAX_MAX_MB,
+  DATA_URL_READ_MIN_MAX_MB,
+  refreshDataUrlReadMaxMb,
+  setDataUrlReadMaxMb
+} from '@/store/data-url-read-max'
 import { $keepAwake, setKeepAwake } from '@/store/keep-awake'
 import { notify, notifyError } from '@/store/notifications'
 import { repoDiscoveryPolicyFromConfig, repoDiscoveryPolicySignature, scanAndRecordRepos } from '@/store/projects'
@@ -21,7 +32,7 @@ import { enumOptionsFor, getNested, isExternalMemoryProvider, sectionFieldEntrie
 import { MemoryConnect } from './memory/connect'
 import { ProviderConfigPanel } from './memory/provider-config-panel'
 import { ModelSettings, ModelSettingsSkeleton } from './model-settings'
-import { EmptyState, SettingsContent, SettingsSkeleton, ToggleRow } from './primitives'
+import { EmptyState, ListRow, SettingsContent, SettingsSkeleton, ToggleRow } from './primitives'
 import { QuickEntrySettings } from './quick-entry-settings'
 
 // On the Voice page, only surface the sub-fields of the *selected* TTS/STT
@@ -305,9 +316,13 @@ export function ConfigSettings({
           <QuickEntrySettings />
         </>
       )}
-      {visibleFields.length === 0 ? (
+      {/* Device-local attach/preview byte cap (main-process IPC guard). Chat is
+          where image-attachment behavior already lives, so this sits above the
+          schema fields for that section. */}
+      {activeSectionId === 'chat' ? <AttachmentSizeSetting /> : null}
+      {visibleFields.length === 0 && activeSectionId !== 'chat' ? (
         <EmptyState description={c.emptyDesc} title={c.emptyTitle} />
-      ) : (
+      ) : visibleFields.length === 0 ? null : (
         <div className="grid gap-1">
           {visibleFields.map(([key, field]) => (
             <div className="scroll-mt-6 rounded-lg" id={`setting-field-${key}`} key={key}>
@@ -345,3 +360,73 @@ export function ConfigSettings({
     </SettingsContent>
   )
 }
+
+/** Free-form MB cap for Desktop's data-URL attach/preview path (main-process). */
+function AttachmentSizeSetting() {
+  const { t } = useI18n()
+  const c = t.settings.config
+  const stored = useStore($dataUrlReadMaxMb)
+  const [draft, setDraft] = useState(String(stored))
+
+  useEffect(() => {
+    void refreshDataUrlReadMaxMb()
+  }, [])
+
+  useEffect(() => {
+    setDraft(String(stored))
+  }, [stored])
+
+  const commit = () => {
+    // An empty draft means "reset to the default", not the 1 MB floor
+    // (Number('') === 0 would otherwise clamp down to the floor).
+    const applied = draft.trim() === '' ? DATA_URL_READ_DEFAULT_MAX_MB : clampDataUrlReadMaxMb(draft)
+
+    // Unchanged: snap the draft back to the stored value and skip the
+    // pointless IPC write + haptic.
+    if (applied === stored) {
+      setDraft(String(stored))
+
+      return
+    }
+
+    void setDataUrlReadMaxMb(applied).then(next => {
+      setDraft(String(next))
+
+      // On a bridge write failure the store keeps the old value; only
+      // celebrate when the new cap actually landed.
+      if (next === applied) {
+        triggerHaptic('selection')
+      }
+    })
+  }
+
+  return (
+    <ListRow
+      action={
+        <div className="flex items-center gap-2">
+          <Input
+            aria-label={c.attachmentSizeLabel}
+            className="w-20"
+            inputMode="numeric"
+            max={DATA_URL_READ_MAX_MAX_MB}
+            min={DATA_URL_READ_MIN_MAX_MB}
+            onBlur={commit}
+            onChange={event => setDraft(event.target.value)}
+            onKeyDown={event => {
+              if (event.key === 'Enter') {
+                event.currentTarget.blur()
+              }
+            }}
+            type="number"
+            value={draft}
+          />
+          <span className="text-[length:var(--conversation-caption-font-size)] text-(--ui-text-tertiary)">
+            {c.attachmentSizeUnit}
+          </span>
+        </div>
+      }
+      description={c.attachmentSizeDesc}
+      title={c.attachmentSizeTitle}
+    />
+  )
+}
diff --git a/apps/desktop/src/global.d.ts b/apps/desktop/src/global.d.ts
index 03af8c62adf0..80c8104376e5 100644
--- a/apps/desktop/src/global.d.ts
+++ b/apps/desktop/src/global.d.ts
@@ -114,6 +114,11 @@ declare global {
       notify: (payload: HermesNotification) => Promise<boolean>
       requestMicrophoneAccess: () => Promise<boolean>
       readFileDataUrl: (filePath: string) => Promise<string>
+      /** Settings → Chat: max size for local files loaded as data URLs (attach/preview). */
+      dataUrlReadMax?: {
+        get: () => Promise<{ defaultMaxMb: number; maxBytes: number; maxMb: number }>
+        set: (maxMb: number) => Promise<{ defaultMaxMb: number; maxBytes: number; maxMb: number }>
+      }
       readFileText: (filePath: string) => Promise<HermesReadFileTextResult>
       selectPaths: (options?: HermesSelectPathsOptions) => Promise<string[]>
       writeClipboard: (text: string) => Promise<boolean>
diff --git a/apps/desktop/src/i18n/en.ts b/apps/desktop/src/i18n/en.ts
index ba1574c78a83..7e973fcc1b8a 100644
--- a/apps/desktop/src/i18n/en.ts
+++ b/apps/desktop/src/i18n/en.ts
@@ -546,7 +546,12 @@ export const en: Translations = {
       imported: 'Config imported',
       invalidJson: 'Invalid config JSON',
       keepAwakeTitle: 'Keep computer awake',
-      keepAwakeDesc: 'Stop this machine from sleeping so long or overnight runs keep going. The display can still dim.'
+      keepAwakeDesc: 'Stop this machine from sleeping so long or overnight runs keep going. The display can still dim.',
+      attachmentSizeTitle: 'Max attachment size',
+      attachmentSizeDesc:
+        'How big a local file Desktop will load for attach and previews, in MB. Default is 16. This is only a limit on this computer. Setting it very high loads the whole file into memory and can freeze or crash the app.',
+      attachmentSizeUnit: 'MB',
+      attachmentSizeLabel: 'Max attachment size in megabytes'
     },
     quickEntry: {
       enabledTitle: 'Quick Entry',
diff --git a/apps/desktop/src/i18n/types.ts b/apps/desktop/src/i18n/types.ts
index bc455ea9cdf2..56ff50769e97 100644
--- a/apps/desktop/src/i18n/types.ts
+++ b/apps/desktop/src/i18n/types.ts
@@ -454,6 +454,10 @@ export interface Translations {
       invalidJson: string
       keepAwakeTitle: string
       keepAwakeDesc: string
+      attachmentSizeTitle: string
+      attachmentSizeDesc: string
+      attachmentSizeUnit: string
+      attachmentSizeLabel: string
     }
     quickEntry: {
       enabledTitle: string
diff --git a/apps/desktop/src/i18n/zh.ts b/apps/desktop/src/i18n/zh.ts
index 6860eadc5300..1b692d40b1d4 100644
--- a/apps/desktop/src/i18n/zh.ts
+++ b/apps/desktop/src/i18n/zh.ts
@@ -756,7 +756,12 @@ export const zh: Translations = {
       imported: '配置已导入',
       invalidJson: '配置 JSON 无效',
       keepAwakeTitle: '保持电脑唤醒',
-      keepAwakeDesc: '阻止本机休眠，让长时间或通宵运行继续进行。屏幕仍可变暗。'
+      keepAwakeDesc: '阻止本机休眠，让长时间或通宵运行继续进行。屏幕仍可变暗。',
+      attachmentSizeTitle: '附件大小上限',
+      attachmentSizeDesc:
+        '桌面端为附件和预览加载本地文件的大小上限（MB）。默认为 16。此限制仅作用于本机。设置过大会将整个文件读入内存，可能导致应用卡死或崩溃。',
+      attachmentSizeUnit: 'MB',
+      attachmentSizeLabel: '附件大小上限（MB）'
     },
     quickEntry: {
       enabledTitle: '快速输入',
diff --git a/apps/desktop/src/store/data-url-read-max.test.ts b/apps/desktop/src/store/data-url-read-max.test.ts
new file mode 100644
index 000000000000..37c0a2996698
--- /dev/null
+++ b/apps/desktop/src/store/data-url-read-max.test.ts
@@ -0,0 +1,63 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import {
+  $dataUrlReadMaxMb,
+  clampDataUrlReadMaxMb,
+  DATA_URL_READ_DEFAULT_MAX_MB,
+  refreshDataUrlReadMaxMb,
+  setDataUrlReadMaxMb
+} from './data-url-read-max'
+
+const desktopWindow = window as unknown as { hermesDesktop?: Window['hermesDesktop'] }
+const initialHermesDesktop = desktopWindow.hermesDesktop
+
+const get = vi.fn(async () => ({ defaultMaxMb: 16, maxBytes: 16 * 1024 * 1024, maxMb: 16 }))
+
+const set = vi.fn(async (maxMb: number) => ({
+  defaultMaxMb: 16,
+  maxBytes: maxMb * 1024 * 1024,
+  maxMb
+}))
+
+beforeEach(() => {
+  desktopWindow.hermesDesktop = { dataUrlReadMax: { get, set } } as unknown as Window['hermesDesktop']
+  $dataUrlReadMaxMb.set(DATA_URL_READ_DEFAULT_MAX_MB)
+  get.mockClear()
+  set.mockClear()
+})
+
+afterEach(() => {
+  desktopWindow.hermesDesktop = initialHermesDesktop
+})
+
+describe('clampDataUrlReadMaxMb', () => {
+  it('defaults invalid input and clamps only the safety range', () => {
+    expect(clampDataUrlReadMaxMb(undefined)).toBe(16)
+    expect(clampDataUrlReadMaxMb(0)).toBe(1)
+    expect(clampDataUrlReadMaxMb(100)).toBe(100)
+    expect(clampDataUrlReadMaxMb(99999)).toBe(4096)
+    expect(clampDataUrlReadMaxMb(32.4)).toBe(32)
+  })
+})
+
+describe('data-url-read-max store', () => {
+  it('loads the main-process value into the atom', async () => {
+    get.mockResolvedValueOnce({ defaultMaxMb: 16, maxBytes: 32 * 1024 * 1024, maxMb: 32 })
+
+    await expect(refreshDataUrlReadMaxMb()).resolves.toBe(32)
+    expect($dataUrlReadMaxMb.get()).toBe(32)
+  })
+
+  it('writes through the bridge and updates the atom', async () => {
+    await expect(setDataUrlReadMaxMb(48)).resolves.toBe(48)
+    expect(set).toHaveBeenCalledWith(48)
+    expect($dataUrlReadMaxMb.get()).toBe(48)
+  })
+
+  it('keeps the last known-good value when the bridge write fails', async () => {
+    set.mockRejectedValueOnce(new Error('boom'))
+
+    await expect(setDataUrlReadMaxMb(48)).resolves.toBe(16)
+    expect($dataUrlReadMaxMb.get()).toBe(16)
+  })
+})
diff --git a/apps/desktop/src/store/data-url-read-max.ts b/apps/desktop/src/store/data-url-read-max.ts
new file mode 100644
index 000000000000..b37556d3fd64
--- /dev/null
+++ b/apps/desktop/src/store/data-url-read-max.ts
@@ -0,0 +1,76 @@
+/**
+ * Max size for local files Desktop loads as data URLs (composer attach, image
+ * previews, etc.). Main owns the real cap + its JSON under userData — this
+ * atom only mirrors it for Settings → Chat. See electron/main.ts
+ * (`hermes:data-url-read-max:*`) and the default/clamp in electron/hardening.ts.
+ */
+
+import { atom } from 'nanostores'
+
+import { notifyError } from '@/store/notifications'
+
+/** Ship default; must match DATA_URL_READ_DEFAULT_MAX_MB in hardening.ts. */
+export const DATA_URL_READ_DEFAULT_MAX_MB = 16
+export const DATA_URL_READ_MIN_MAX_MB = 1
+/** Typo / absurd-value guard only — large values can still OOM the app. */
+export const DATA_URL_READ_MAX_MAX_MB = 4096
+
+export function clampDataUrlReadMaxMb(value: unknown): number {
+  const parsed = Number(value)
+
+  if (!Number.isFinite(parsed)) {
+    return DATA_URL_READ_DEFAULT_MAX_MB
+  }
+
+  return Math.min(DATA_URL_READ_MAX_MAX_MB, Math.max(DATA_URL_READ_MIN_MAX_MB, Math.round(parsed)))
+}
+
+export const $dataUrlReadMaxMb = atom<number>(DATA_URL_READ_DEFAULT_MAX_MB)
+
+export async function refreshDataUrlReadMaxMb(): Promise<number> {
+  const api = window.hermesDesktop?.dataUrlReadMax
+
+  if (!api) {
+    return $dataUrlReadMaxMb.get()
+  }
+
+  try {
+    const result = await api.get()
+    const maxMb = clampDataUrlReadMaxMb(result.maxMb)
+    $dataUrlReadMaxMb.set(maxMb)
+
+    return maxMb
+  } catch {
+    return $dataUrlReadMaxMb.get()
+  }
+}
+
+export async function setDataUrlReadMaxMb(maxMb: number): Promise<number> {
+  const next = clampDataUrlReadMaxMb(maxMb)
+  const api = window.hermesDesktop?.dataUrlReadMax
+
+  if (!api) {
+    $dataUrlReadMaxMb.set(next)
+
+    return next
+  }
+
+  try {
+    const result = await api.set(next)
+    const applied = clampDataUrlReadMaxMb(result.maxMb)
+    $dataUrlReadMaxMb.set(applied)
+
+    return applied
+  } catch (error) {
+    // Leave the atom at the last known-good value and surface the failure —
+    // an optimistic set here would show a cap that was never persisted and
+    // silently reverts on restart.
+    notifyError(error, 'Could not save the max attachment size')
+
+    return $dataUrlReadMaxMb.get()
+  }
+}
+
+if (typeof window !== 'undefined' && window.hermesDesktop?.dataUrlReadMax) {
+  void refreshDataUrlReadMaxMb()
+}