[Ladislau Szomoru (lszomoru)]

Phase 2 of #345429, for Linux, after #346270 for Windows.

The Linux test jobs of pull requests now mount the workspace image that pr-workspace-images.yml builds on main (an ext4 volume on a loop device at the parent of the workspace), instead of restoring the node_modules and Playwright caches. With an image, the checkout keeps its untracked files and reuses its .git, and the usual install steps run on top of its node_modules, so pnpm installs only what changed since the commit of the image. Without an image, or on any error, the jobs set up as before. macOS follows in its own pull request.

What changed

• pr-linux-test.yml: before the checkout, the jobs download the image scripts at their commit (exactly as the Linux job of pr-workspace-images.yml does, which a test now also checks for Linux), set up Node.js, and restore the image (image.ts restore --timeout-seconds 240, within the 5 minutes of the step; on failure it unmounts the image and detaches the loop device). With an image, the node_modules cache and Playwright cache steps are skipped (the Playwright action would point PLAYWRIGHT_BROWSERS_PATH into the workspace instead of the image), and the checkout uses clean: false.
• The install steps are unchanged and run on top of the image: the build root install, then the root install, whose setup-env.sh reuses the sysroots, Clang and libc++ in the .build folder of the image. The apt packages (xvfb, libkrb5-dev, …) aren't in the image and are installed as before.
• pr.yml: linux-tests gets actions: read, to find and download the images, and passes workspace_image_branch: ${{ github.base_ref }}, so that pull requests to release branches look for images of their own branch, find none, and set up as before.
• No step compares the dependencies with the image (the prototype's image.ts deps, which no longer exists).
• The README of the images and the header of pr-workspace-images.yml follow. build/ripple/vscode.jsonc already lists .github/workflows/workspace_image/** since ci: start the Windows PR test jobs from the workspace images #346270.

What to look for in the checks of this pull request

• In each Linux job: "Restore the workspace image" finds the image of main, mounts it on a loop device and sets used=true, and the job summary reports the restore; Restore node_modules cache and Restore Playwright browsers are skipped; Install dependencies prints "Using cached client sysroot"/"Using cached remote sysroot" and installs nothing new; Setup Electron keeps the prepared Electron when its inputs match; Install Playwright Chromium downloads nothing.
• The time from the start of a job to its first test step, against the same jobs of recent pull requests that hit the node_modules cache.

Validation:

• cd build && node --test lib/test/detectMissingCaches.test.ts lib/test/detectChanges.test.ts lib/test/workspaceImage.test.ts lib/test/agentHostTestSelection.test.ts: 35 passed
• go run github.com/rhysd/actionlint/cmd/actionlint@latest -shellcheck= .github/workflows/pr-linux-test.yml .github/workflows/pr.yml .github/workflows/pr-workspace-images.yml: only unknown custom runner labels
• The native build inputs (NATIVE_BUILD_INPUTS of image.ts) of the newest Linux image of main are the same as on this branch.

[Copilot]

🔵 Needs a closer look

No Linux CI results were provided to validate image-hit and fallback runs, timeout cleanup, loop-device mounting, or checkout and native dependency reuse.

No open issues 🎉

What changed in this PR

Extends workspace-image reuse to Linux PR test jobs, following the Windows rollout, to reduce setup time while preserving the existing cache-based setup when an image is unavailable or restoration fails.

Changes:

• Restore Linux workspace images before checkout, preserve their dependencies, and skip redundant dependency and Playwright cache restores.
• Grant Linux jobs image-download permissions and select images from the PR’s target branch.
• Extend script-download consistency tests to Linux and update rollout documentation.

File	Description
build/​lib/​test/​workspaceImage.test.ts	Adds Linux coverage to the image-script download consistency test.
.github/​workflows/​workspace_image/​README.md	Documents Linux adoption and reuse of image-provided build tools.
.github/​workflows/​pr.yml	Grants image-download permissions and passes the target branch.
.github/​workflows/​pr-workspace-images.yml	Updates the header comment to reflect Linux adoption.
.github/​workflows/​pr-linux-test.yml	Adds image restoration, conditional checkout cleaning, and cache bypasses.

_{Review effort: Balanced}