Desktop file attachment selection was inlining every selected file as a data URL before sending the websocket message. Large multi-file sends could inflate the renderer request body by tens of megabytes before the server had a chance to materialize uploads.
Route Tauri file selection through the native dialog so desktop sends absolute paths, while preserving browser fallback data URLs for H5. Cover both active-session and draft-session composers plus a payload-size regression case.
Constraint: Browser/H5 cannot rely on local absolute file paths, so the existing FileReader fallback remains for non-Tauri runtimes.
Rejected: Raise websocket/body limits | would keep renderer memory pressure and still send file bytes unnecessarily.
Confidence: high
Scope-risk: narrow
Directive: Do not reintroduce FileReader data URLs for Tauri desktop file-picker attachments without measuring websocket payload size.
Tested: cd desktop && bun run test src/lib/composerAttachments.test.ts src/components/chat/ChatInput.test.tsx src/pages/EmptySession.test.tsx
Tested: /tmp complex-project reproduction showed 12x3MB old inline payload at 50,333,174 bytes versus path-only payload around 1-2KB
Not-tested: Full desktop lint/build due unrelated existing Sidebar.tsx type errors in the dirty worktree
Related: https://github.com/NanmiCoder/cc-haha/issues/444
