chore(deps): bump to vitest 4 and adjust tests after the upgrade

[samuv]

Breaking Changes Fixed

Vitest 4 requires vi.fn() mocks to use function/class constructors instead of arrow functions.

Changes

• Updated Vitest monorepo to v4
• Added memfs for file system mocking
• Fixed mock implementations across all test files:
  • Changed vi.fn().mockImplementation(() => {}) to vi.fn(function Mock() {})
  • Updated Node.js built-in module mocks (node:child_process, node:fs, node:net) to use importOriginal and share mock instances between named/default exports
  • Migrated to memfs for file system mocking

Files Updated

Renderer:

• use-chat-streaming.test.ts, use-download-file.test.ts, logs-tab.test.tsx, group-selector-form.test.tsx, use-mcp-secrets.test.ts, theme-provider.test.tsx

Main:

• auto-update.test.ts, graceful-exit.test.ts, toolhive-manager.test.ts

All tests passing ✅

[Copilot]

Pull Request Overview

This PR upgrades Vitest from v3.x to v4.x and introduces memfs for mocking the file system in tests. Key changes include updating test mock implementations to use named functions for better debugging and replacing direct node:fs mocks with memfs.

• Upgraded vitest from ^3.1.4 to ^4.0.0 and @vitest/coverage-istanbul from ^3.1.4 to ^4.0.0
• Added memfs (^4.50.0) for file system mocking
• Refactored vi.fn().mockImplementation() to use named function expressions in test mocks
• Created reusable __mocks__ files for fs and fs/promises using memfs
• Updated test setup in toolhive-manager.test.ts to use vol from memfs for file system state management

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
package.json	Updated Vitest and coverage dependencies to v4.x, added memfs package
pnpm-lock.yaml	Updated lockfile with new dependency versions and their transitive dependencies
renderer/src/features/meta-mcp/components/tests/group-selector-form.test.tsx	Refactored mock to use named function expression
renderer/src/features/chat/hooks/tests/use-chat-streaming.test.ts	Refactored mock to use named function expression
renderer/src/common/hooks/tests/use-mcp-secrets.test.ts	Refactored mocks to use named function expressions
renderer/src/common/hooks/tests/use-download-file.test.ts	Refactored Blob mock to use named function expression
renderer/src/common/components/theme/tests/theme-provider.test.tsx	Refactored matchMedia mock to use named function expression
renderer/src/common/components/settings/tabs/tests/logs-tab.test.tsx	Refactored Blob mock to use named function expression
main/src/tests/toolhive-manager.test.ts	Replaced existsSync mocks with memfs, refactored mocks to use named functions, exported binPath for testing
main/src/tests/graceful-exit.test.ts	Refactored ElectronStore mock to use named function expression
main/src/tests/auto-update.test.ts	Refactored ElectronStore mock to use named function expression
mocks/fs/promises.cjs	Created mock for node:fs/promises using memfs
mocks/fs.cjs	Created mock for node:fs using memfs

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported