diff --git a/config/electron-builder.config.cjs b/config/electron-builder.config.cjs
index 4fa904ab6d4..577cbd97a93 100644
--- a/config/electron-builder.config.cjs
+++ b/config/electron-builder.config.cjs
@@ -129,6 +129,9 @@ module.exports = {
     '!out/**/*.test.js',
     // Why: Vite's manifest is only used to project the paired web client.
     '!out/renderer/.vite{,/**/*}',
+    // Why: out/electron-dev caches `pnpm dev`'s per-branch Electron.app copies (~270MB each).
+    // CI never creates it, but packaging on a machine that has run dev would pack them all.
+    '!out/electron-dev{,/**/*}',
     '!electron.vite.config.{js,ts,mjs,cjs}',
     '!{.eslintcache,eslint.config.mjs,.prettierignore,.prettierrc.yaml,CHANGELOG.md,README.md}',
     '!{.env,.env.*,.npmrc,pnpm-lock.yaml}',
diff --git a/config/scripts/electron-builder-config.test.mjs b/config/scripts/electron-builder-config.test.mjs
index 33578580dae..75c3898858e 100644
--- a/config/scripts/electron-builder-config.test.mjs
+++ b/config/scripts/electron-builder-config.test.mjs
@@ -75,6 +75,25 @@ describe('electron-builder config', () => {
     expect(packs('out/main/examples/index.js')).toBe(true)
   })
 
+  // Why: out/electron-dev holds `pnpm dev`'s cached Electron.app copies (~270MB per branch).
+  // CI never creates it, so only a local package would have hit this -- silently, as bulk.
+  it('keeps cached dev Electron bundles out of app.asar', () => {
+    const matcher = new FileMatcher('/app', '/dest', (value) => value, electronBuilderConfig.files)
+    matcher.prependPattern('**/*')
+    const isPacked = matcher.createFilter()
+    const packs = (repoPath) => isPacked(join('/app', repoPath), { isDirectory: () => false })
+
+    for (const devBundlePath of [
+      'out/electron-dev/1a2b3c4d5e6f/Orca: dev.app/Contents/MacOS/Electron',
+      'out/electron-dev/1a2b3c4d5e6f/orca-dev-electron-app.json'
+    ]) {
+      expect(packs(devBundlePath)).toBe(false)
+    }
+    // The real build outputs sit beside it under out/ and must still ship.
+    expect(packs('out/main/index.js')).toBe(true)
+    expect(packs('out/renderer/index.html')).toBe(true)
+  })
+
   it('keeps runtime resources available through extraResources', () => {
     const bundledPluginResources = expect.objectContaining({
       from: 'resources/plugins/launch',