ci: shadow typecheck/unit/integration jobs on Blacksmith

[gantoine]

Summary

• Adds a runner matrix dimension to typecheck, unit-test, and integration-test so each job can run head-to-head on GitHub-hosted and Blacksmith runners for apples-to-apples comparison data. Inspired by PostHog/posthog#54559.
• Gated behind repo variable BLACKSMITH_SHADOW_ENABLED so shadows can be toggled without a code change. Pairs ubuntu-latest ↔ blacksmith-4vcpu-ubuntu-2404 and macos-latest ↔ blacksmith-6vcpu-macos-latest.
• Shadow entries are continue-on-error: true so Blacksmith failures don't block PRs. Cache keys are scoped to matrix.runner to avoid cross-runner poisoning, and the Playwright report only uploads from the macos-latest primary.

Before this is useful

• Set repo variable BLACKSMITH_SHADOW_ENABLED=true in Settings → Variables → Actions.
• Install the Blacksmith GitHub App on the repo.
• Update branch protection: matrix expansion renames required checks (e.g. typecheck → typecheck (ubuntu-latest)), and Blacksmith entries should be excluded from required checks.

Test plan

• Leave BLACKSMITH_SHADOW_ENABLED unset and confirm this PR's CI still runs exactly one entry per job (original behavior).
• After flipping the flag, confirm both runners pick up jobs and produce paired durations on the same SHA.
• Confirm the Playwright report artifact uploads only once on failure (from macos-latest).

🤖 Generated with Claude Code

[greptile-apps]

_{Reviews (1): Last reviewed commit: "ci: shadow typecheck/unit/integration jo..." | Re-trigger Greptile}

[Copilot]

Pull request overview

Adds “shadow” CI executions so typecheck/unit/integration jobs can run in parallel on GitHub-hosted vs Blacksmith runners (optionally enabled via BLACKSMITH_SHADOW_ENABLED) to compare performance and reliability without blocking PRs.

Changes:

• Introduces a runner matrix for typecheck, unit-test, and integration-test, gated by vars.BLACKSMITH_SHADOW_ENABLED.
• Marks Blacksmith matrix entries as continue-on-error and disables fail-fast for the matrix.
• Scopes Playwright/Electron cache keys to matrix.runner and restricts Playwright report uploads to the primary macOS runner.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
.github/workflows/typecheck.yml	Adds runner matrix + shadow execution for typecheck on Blacksmith.
.github/workflows/test.yml	Adds runner matrices for unit/integration; adjusts caching and Playwright artifact upload behavior for shadows.

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[charlesvien]

LGTM! TY!

[Copilot]

Pull request overview

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

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[Copilot]

Same as for unit-test: without an explicit job name, the matrix-expanded check will typically show up as integration-test (runner: …), not integration-test (macos-latest). Consider adding a name that includes matrix.runner so required check names are clear and match the PR’s guidance.

[gantoine]

@copilot why are the 3 pending checks not reporting?

[Copilot]

@copilot why are the 3 pending checks not reporting?

The root cause is that GitHub's matrix strategy automatically appends (ubuntu-latest) / (macos-latest) to job names — even when there's only a single entry in the matrix (i.e. shadow disabled). Branch protection rules still expect the original names (typecheck, unit-test, integration-test), so those required checks are never satisfied and stay "pending".

Fixed in 760791c by adding an explicit name: to each job that evaluates to the original name for the primary runner and to <job> (<runner>) for Blacksmith shadows:

name: ${{ matrix.runner == 'ubuntu-latest' && 'typecheck' || format('typecheck ({0})', matrix.runner) }}

This keeps required check names stable whether shadow is on or off, and gives shadow entries a distinct name so they don't conflict.