improvement(ci): partition desktop acceptance across four runners

Author: waleedlatif1

.github/CI.md

@@ -63,7 +63,7 @@ The long-import and lease-expiration checks remain: they prove distinct survival
 
 Local planner validation is `bun run test:scripts scripts/ci-changes.test.ts scripts/ci-gate.test.ts`. It executes real Turbo queries in small Git fixtures; no application build or database is required. Full builds, services, browser suites, and Electron checks run on hosted CI.
 
-The separate `desktop-e2e` workflow retains its desktop-specific path filters. Its macOS shell smoke suite runs whole files across three isolated runners, with one worker per runner. `scripts/desktop-e2e.ts` asks Playwright to discover the complete suite, then assigns longer files first to the currently lightest shard using `apps/desktop/e2e-durations.json`. Exact escaped file filters preserve serial fixtures. Unmeasured files receive the median measured weight, deleted files cannot select tests, and invalid or empty selections fail. Normal local runs, packaging smoke and the weekly Electron canary keep their existing commands.
+The separate `desktop-e2e` workflow retains its desktop-specific path filters. Its macOS shell smoke suite runs whole files across four isolated runners, with one worker per runner. The matrix owns the partition count; job names and runner arguments use `strategy.job-total`. `scripts/desktop-e2e.ts` asks Playwright to discover the complete suite, then assigns longer files first to the currently lightest shard using `apps/desktop/e2e-durations.json`. Exact escaped file filters preserve serial fixtures. Unmeasured files receive the median measured weight, deleted files cannot select tests, and invalid or empty selections fail. Normal local runs, packaging smoke and the weekly Electron canary keep their existing commands.
 
 The current weights are median test durations in seconds from runs [41496623284](https://github.com/simstudioai/sim/actions/runs/41496623284), [41497346251](https://github.com/simstudioai/sim/actions/runs/41497346251), and [41502340540](https://github.com/simstudioai/sim/actions/runs/41502340540). Refresh them from complete `desktop-smoke-reports-*` artifacts when the workload changes: sum `tests[].results[].duration` by `spec.file` in each run, take the median across runs, and divide milliseconds by 1,000. The weights steer scheduling only; Playwright discovery owns coverage. Before adopting new weights, compare repeated paired runs and the complete case/status multiset, including skipped cases and retries.
 

.github/workflows/desktop-e2e.yml

@@ -1,6 +1,6 @@
 name: desktop-e2e
 
-# Smoke coverage of the real Electron shell on desktop changes. Three isolated runners
+# Smoke coverage of the real Electron shell on desktop changes. Isolated runners
 # partition complete test files by measured duration; workers remain serial per runner.
 # The weekly
 # advisory canary against electron@latest so Chromium-cadence breakage surfaces
@@ -104,14 +104,14 @@ jobs:
         run: bun run scripts/build-native.ts --computer-use
 
   e2e:
-    name: e2e (${{ matrix.shard }}/3)
+    name: e2e (${{ matrix.shard }}/${{ strategy.job-total }})
     if: github.event_name != 'schedule' && github.event_name != 'push'
     runs-on: macos-26
     timeout-minutes: 30
     strategy:
       fail-fast: false
       matrix:
-        shard: [1, 2, 3]
+        shard: [1, 2, 3, 4]
     steps:
       - name: Checkout code
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v6
@@ -160,7 +160,7 @@ jobs:
 
       - name: Run Playwright _electron smoke suite
         working-directory: apps/desktop
-        run: bun run ../../scripts/desktop-e2e.ts ${{ matrix.shard }}/3
+        run: bun run ../../scripts/desktop-e2e.ts ${{ matrix.shard }}/${{ strategy.job-total }}
         env:
           PLAYWRIGHT_JSON_OUTPUT_FILE: test-results/desktop-smoke.json
           BACKGROUND_EXECUTOR_REPORT_PATH: test-results/background-executor-report.json