ci(test): install the Electron binary before the unit tests

pnpm runs build scripts only for allow-listed packages, so electron's
postinstall never downloads its binary in CI. require('electron') then
fetches it lazily, and parallel Jest workers that spawn Electron
(epg-source-metadata, playlist.operations) race on that download: one
executes the half-written file and fails with ETXTBSY. Fetch the binary
once after pnpm install; install.js skips an existing binary.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -407,6 +407,16 @@ jobs:
             - name: Install dependencies
               run: pnpm install --frozen-lockfile
 
+            # pnpm only runs build scripts for allow-listed packages
+            # (pnpm-workspace.yaml), so electron's postinstall never fetches
+            # its binary. `require('electron')` then downloads it lazily, and
+            # parallel Jest workers that spawn Electron race on the same
+            # download: one executes the half-written binary (ETXTBSY).
+            # Fetch it once before any test runs; install.js skips an
+            # existing binary.
+            - name: Install the Electron binary
+              run: node node_modules/electron/install.js
+
             - name: Validate agent guidance
               run: pnpm run agents:validate