test: run the test suite on Node 26

[beeman]

mock-fs patches Node fs internals and throws at import time on Node 26 (tschaub/mock-fs#447), which took down search-and-replace.test.ts as a whole and failed the Test & Lint on Node current job on every PR — current resolves to 26.8.1 since Node 26 shipped. All actual tests pass; only the mock-fs import crashes.

mock-fs was used in exactly one test, to create an unreadable (mode 0o000) file so readFile fails. That call is now stubbed via a vitest passthrough mock of node:fs/promises instead, and mock-fs and @types/mock-fs are removed. Every other test in the file already runs against a real temp directory.

Also adds an explicit 26 entry to the test matrix so Node 26 stays covered after current rolls to 27 in October.

Verified locally on Node 26.8.1: full pnpm test (lint, types, vitest with coverage) passes, 165/165 tests.

Replaces #289, same diagnosis. No changeset: dev-dependency and test changes only, nothing ships to users.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 216c803

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/create-solana-dapp@290

commit: 216c803

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge; the dependency removal is complete, and the replacement mock exercises the intended error path without affecting other tests.

Summary

This PR restores Node 26 test compatibility and keeps that runtime explicitly covered in CI.

• Replaces the incompatible mock-fs usage with a scoped Vitest passthrough mock of node:fs/promises.
• Removes the unused mock-fs packages and corresponding lockfile entries.
• Adds Node 26 to the workflow test matrix alongside the rolling current release.

_{Reviews (2) · Last reviewed commit: "test: run the test suite on Node 26"}