Expose platform metadata on WaveEnv and preview mocks

[Copilot]

WaveEnv did not surface platform information, so platform-aware behavior could not be added through the shared environment contract. This updates the contract, production implementation, and preview mock to carry platform state without wiring it into any consumers yet.

• WaveEnv contract

  • Add platform: NodeJS.Platform
  • Add isWindows() and isMacOS() helpers

• Production implementation

  • Populate platform from PLATFORM in frontend/util/platformutil.ts
  • Forward isWindows / isMacOS from the same utility into makeWaveEnvImpl()

• Preview mock

  • Add optional platform override to MockEnv
  • Default mock platform to macOS
  • Expose platform, isWindows(), and isMacOS() on the mock env
  • Preserve platform overrides through applyMockEnvOverrides()

Example:

const env = useWaveEnv();

env.platform;      // "darwin" | "win32" | ...
env.isMacOS();     // boolean
env.isWindows();   // boolean

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[kilo-code-bot]

WARNING: The getPlatform function should be defined AFTER the ...overrides.electron spread to ensure it always returns the correct platform value, even when users override other electron properties.

Currently, if a user passes getPlatform in overrides.electron, it will override the platform-based implementation. The correct order should be:

electron: {
    ...previewElectronApi,
    ...overrides.electron,
    getPlatform: () => platform,
},

[kilo-code-bot]

Code Review Summary

Status: 1 Issue Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	0

Issue Details (click to expand)

WARNING

File	Line	Issue
frontend/preview/mock/mockwaveenv.ts	160	The getPlatform function is defined before ...overrides.electron, allowing user overrides to potentially replace the mock platform value. Move it after the spread to ensure the mock platform is always used.

Files Reviewed (3 files)

• frontend/app/waveenv/waveenv.ts - Type extension adds platform, isWindows, isMacOS
• frontend/app/waveenv/waveenvimpl.ts - Implementation correctly uses platform utilities
• frontend/preview/mock/mockwaveenv.ts - Mock support added (has existing warning)