Enhance CI workflow with E2E sharding and report merging

[paustint]

Implement sharding for end-to-end tests and merge reports into a single HTML report, improving CI efficiency and test result visibility.

[Copilot]

Pull request overview

This PR updates the Jetstream E2E CI pipeline to run Playwright tests in shards and then merge shard outputs into a single HTML report artifact, aiming to reduce overall CI time and improve test report visibility.

Changes:

• Switch Playwright CI reporter from html to blob so shard results can be merged later.
• Shard the E2E job into 4 matrix runs and upload a blob report artifact per shard.
• Add a follow-up job to download all blob reports, merge them, and upload a single HTML report artifact.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
apps/jetstream-e2e/playwright.config.ts	Uses blob reporter in CI to enable post-run report merging.
.github/workflows/ci.yml	Adds Playwright sharding, per-shard blob artifacts, and a merge job producing one HTML report.

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[paustint]

@copilot - fix the ci job, the mer process does not work

Run npx playwright merge-reports --reporter html ./all-blob-reports
Error: Directory does not exist: /home/runner/work/jetstream/jetstream/all-blob-reports
    at mergeReports (/home/runner/work/jetstream/jetstream/node_modules/playwright/lib/program.js:260:11)
    at async i.<anonymous> (/home/runner/work/jetstream/jetstream/node_modules/playwright/lib/program.js:133:7)
Error: Process completed with exit code 1.

[Copilot]

@copilot - fix the ci job, the mer process does not work

...

Fixed in ef7d3f7. The issue was that Playwright resolves the blob reporter's outputDir relative to the config file directory (apps/jetstream-e2e/), so the blob report was written to apps/jetstream-e2e/blob-report — but the upload step was looking for blob-report at the repo root. Updated the upload path to apps/jetstream-e2e/blob-report and added a mkdir -p safeguard in the merge step.