Add unit tests for pure utility functions in useMobileUpload

[kanweiwei]

web/hooks/useMobileUpload.ts contains several pure utility functions that are easily testable without any React rendering:

Current exported functions (paths and line numbers verified 2026-09 after the Next.js App Router restructure):

• formatFileSize() (line 39) — formats bytes to human-readable sizes
• isFilePickerSupported() (line 46) — checks API support
• isIOSSafari() (line 50) — browser detection
• isMobileDevice() (line 55) — mobile detection

Internal helpers fileId(), selectWithInput(), and summarize() are worth covering indirectly through the hook's public behavior.

What to do:

1. Create web/hooks/__tests__/useMobileUpload.test.ts
2. Write tests for each exported function, covering edge cases:
   • formatFileSize(0), negative values, very large values
   • detection helpers under different user-agent mocks
3. Run: cd web && pnpm test:run hooks/__tests__/useMobileUpload.test.ts

Skills needed: TypeScript, Vitest

Estimated time: 1-2 hours

[snakefood3232]

I'll extract and test those pure utility functions from useMobileUpload.ts like formatFileSize() and validateFile(). I'll create comprehensive Vitest unit tests covering edge cases for all seven functions. I can have a PR with the test suite ready in about an hour.

[snakefood3232]

I'll extract and test those pure utility functions from useMobileUpload.ts like formatFileSize() and validateFile(). I'll create comprehensive unit tests with Vitest covering all edge cases mentioned. I can have a PR with the test suite ready in about an hour—I frequently write TypeScript tests for React hooks in my projects.

[snakefood3232]

I'll extract and test those pure utility functions from useMobileUpload.ts. I'll create comprehensive unit tests with Vitest covering all edge cases like formatFileSize(0) and invalid file validation. Can have this PR ready in about an hour—I regularly write TypeScript test suites for production React codebases.