fix(desktop): serve local hermes-media ranges so chat video can seek

Electron's file:// loader ignores Range, so long clips stay unseekable even
though media-range.ts already landed. Wire fetchLocal through that helper.

apps/desktop/electron/main.ts

@@ -262,6 +262,7 @@ import {
 } from './managed-ssh-update'
 import { registerMcpOauthCallbackIpc } from './mcp-oauth-callback-ipc'
 import { createMediaProtocolHandler, MEDIA_PROTOCOL } from './media-protocol'
+import { fetchLocalMedia } from './media-range'
 import { createNativeAccessTokenCoordinator, NativeAuthChangedError } from './native-access-token'
 import { oauthSessionIsLive, resolveJsonBody, resolveReadinessProbeAuth } from './native-auth-decisions'
 import {
@@ -1366,13 +1367,10 @@ protocol.registerSchemesAsPrivileged([
 function registerMediaProtocol() {
   const handler = createMediaProtocolHandler({
     ensureRemoteBearer: baseUrl => ensureNativeAccessToken(baseUrl),
-    fetchLocal: (resolvedPath, headers, method) =>
-      electronNet.fetch(pathToFileURL(resolvedPath).toString(), {
-        bypassCustomProtocolHandlers: true,
-        credentials: 'omit',
-        headers,
-        method
-      }),
+    // Answer local files ourselves: Electron's file:// loader ignores Range and
+    // returns the whole body as 200 without Accept-Ranges, which makes <video>
+    // unseekable (seekable=[0,0]).
+    fetchLocal: fetchLocalMedia,
     fetchRemote: (url, headers, method) =>
       electronNet.fetch(url, {
         bypassCustomProtocolHandlers: true,

apps/desktop/electron/media-range.ts

@@ -174,3 +174,20 @@ export async function buildLocalMediaResponse(
 
   return new Response(stream({ end: range.end, start: range.start }), { headers, status: 206 })
 }
+
+/**
+ * Production `fetchLocal` for `hermes-media://stream/…`.
+ *
+ * Electron's `file://` loader ignores `Range` and answers `200` with the whole body, so Chromium
+ * reports `video.seekable` as `[0, 0]`. Pass this into the media-protocol handler instead.
+ */
+export function fetchLocalMedia(
+  resolvedPath: string,
+  headers: Headers,
+  method: string
+): Promise<Response> {
+  return buildLocalMediaResponse(resolvedPath, {
+    method,
+    rangeHeader: headers.get('range')
+  })
+}