# Hybrid Download Model + Auto-Defocus URL Input

## Task Description
Two user-requested improvements:
1. **Hybrid download model**: Download a low-resolution (≤360p H.264+AAC) version for immediate preview/scrubbing/waveform/thumbnail generation, while downloading the best available quality in the background for export. Clips are cut from the best-quality file.
2. **Auto-defocus URL input**: After pasting a URL and triggering submit, blur the input field so keyboard shortcuts (I, O, etc.) don't accidentally modify the URL.

## Changes Made

### Session State Refactor (`src/lib/stores/videoSession.svelte.ts`)
- Replaced single `localFilePath`/`downloadProgress`/`downloadStatus` with dual-track state:
  - `previewFilePath`/`previewProgress`/`previewStatus` — for the 360p preview
  - `exportFilePath`/`exportProgress`/`exportStatus` — for the best-quality export
- Preview format: `bv*[vcodec^=avc1][height<=360]+ba[acodec^=mp4a]/b[ext=mp4][height<=360]/worst[ext=mp4]/worst`
- Export format: `bv*+ba/b` (best available, any codec since ffmpeg handles export)
- `beginDownload()` now:
  1. Checks cache for preview → downloads if needed → triggers post-processing (waveform, thumbnails, keyframes)
  2. Checks cache for export → downloads in background (fire-and-forget)
- Files stored in separate subdirectories: `video-clipper/preview/` and `video-clipper/export/`

### Rust Backend (`src-tauri/src/commands/video.rs`)
- `start_download` now accepts `format_spec` and `variant` parameters
- `check_cached_download` now accepts a `variant` parameter to check the correct subdirectory
- Helper `variant_dir()` builds `$TEMP/video-clipper/{variant}/` paths
- Diagnostic logging includes variant name for easier debugging

### Download Manager (`src-tauri/src/services/download_manager.rs`)
- `start_download` now accepts `format_spec: &str` parameter instead of hardcoding format selection
- Format string passed through from the frontend call

### Frontend Bindings (`src/lib/bindings/video.ts`)
- `startDownload` now takes `formatSpec` and `variant` parameters
- `checkCachedDownload` now takes a `variant` parameter

### VideoPlayer (`src/lib/components/VideoPlayer.svelte`)
- Uses `previewFilePath`/`previewStatus` instead of old single-track fields
- Download progress shows "Downloading preview…" label

### ExportDialog (`src/lib/components/ExportDialog.svelte`)
- Uses `exportFilePath`/`exportStatus`/`exportProgress` for export readiness
- Shows "Downloading best quality (X%)…" while export download is in progress

### StatusBar (`src/lib/components/StatusBar.svelte`)
- Shows dual progress: preview download → export download → ready to export
- Contextual status messages for each download phase

### UrlInput (`src/lib/components/UrlInput.svelte`)
- Added `bind:this={inputEl}` reference to input element
- `blurInput()` called at the start of `handleSubmit()` — defocuses immediately on paste/enter
- Keyboard shortcuts (I, O, etc.) now work immediately after submitting a URL

## Lessons Learned
- Storing preview and export files in separate subdirectories (`preview/`, `export/`) keeps cache management clean and avoids filename collisions between quality variants.
- Fire-and-forget pattern for background export download (`.catch()` at call site) keeps the preview flow responsive without blocking on the best-quality download.
- The `variant` parameter threading from frontend → Rust command → download manager keeps the API clean and extensible for future quality tiers.

## Follow-Up Items
- Consider showing export download progress in the timeline/player area as a subtle indicator
- The export format `bv*+ba/b` may download VP9/WebM — this is fine for ffmpeg export but won't play in WKWebView. The preview file handles playback.
- Old flat `video-clipper/` cache was cleared; users with existing caches in the old location won't get cache hits (harmless — just re-downloads)