fix: about dialog, cache paths, keyframes, reprocess always uses low-res

- Replace native macOS About menu with custom Svelte dialog via Tauri event
- Inline SVG icon in AboutDialog (fixes broken image in webview)
- Align cache directory with Tauri $APPDATA, add to asset protocol scope
- Fix ffprobe 8.x keyframe parsing (skip_frame nokey, flexible parser)
- Copy caption files into cache dir when outside cache path
- Add -y flag to ffmpeg thumbnail extraction (prevent hang on re-extract)
- Reprocess always uses preview (low-res) file, never HQ export
- Prefer cached preview file for analysis even when HQ is cached
- Guard upgrade toast when already on HQ

Co-authored-by: Cursor <cursoragent@cursor.com>

chat-summaries/2026-09-22_14-50-v0.1.2-polish-summary.md

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+# v0.1.2 Polish — Placeholders, Auto-Upgrade, Analysis Cache
+
+**Date**: 2026-09-22 14:50 ET
+**Duration**: ~20 minutes (brainstorm) + ~20 minutes (execution)
+**Version**: 0.1.1 → 0.1.2
+**Commits**: 2f81011..925a3fc (11 commits)
+
+## Task Description
+
+Three polish features for v0.1.2:
+1. Fix misleading "Generating Waveform…" / "Generating Thumbnails…" placeholder text shown in the timeline before any video is loaded
+2. Automatically use cached HQ video files instead of prompting user to "Upgrade" when the export file is already downloaded
+3. Cache video analysis results (waveforms, keyframes, thumbnails, captions) to avoid reprocessing the same video on reload
+
+## Changes Made
+
+### Feature 1: Idle-State Placeholder Text
+- **`src/lib/timeline/renderer.ts`**: Added `hasVideo` boolean parameter to `drawTimeline()` and `showLabel` to `drawPlaceholderLane()`. When no video is loaded, timeline lanes show empty backgrounds without misleading "Generating…" text.
+- **`src/lib/components/Timeline.svelte`**: Passes `session.status === 'ready'` as the `hasVideo` argument.
+
+### Feature 2: Auto-Use Cached HQ Video
+- **`src/lib/stores/videoSession.svelte.ts`**: Restructured `beginDownload()` to check export (HQ) cache before preview cache. When HQ file exists on disk, it's used directly as the active video — no preview download, no upgrade toast. The upgrade toast is preserved for mid-session HQ completions (to avoid jarring video source swaps during playback).
+
+### Feature 3: Analysis Cache System
+
+**New Rust service** (`src-tauri/src/services/cache_manager.rs`):
+- Cache stored at `~/Library/Application Support/gui-video-clipper/cache/`
+- Videos keyed by SHA-256 URL hash (first 16 hex chars)
+- JSON manifest per video with waveform tiers, keyframe positions, thumbnail spritesheets, caption paths
+- Functions: `load_manifest`, `save_manifest`, `clear_cache_entry`, `clear_all_cache`, `get_cache_stats`
+- 5 unit tests for URL hashing and path computation
+
+**New IPC commands** (`src-tauri/src/commands/cache.rs`):
+- `load_cached_analysis` / `save_analysis_to_cache` / `clear_video_cache` / `clear_all_cache` / `get_cache_stats` / `get_thumbnail_cache_dir` / `get_caption_cache_dir`
+- Path resolution: manifest stores relative paths, IPC layer resolves to absolute for frontend
+
+**Updated `extract_thumbnails`**: Added optional `output_dir` parameter so thumbnails can be directed to cache directory instead of random temp dir.
+
+**TypeScript bindings** (`src/lib/bindings/cache.ts`): Full wrapper layer for all cache IPC commands.
+
+**Frontend integration** (`src/lib/stores/videoSession.svelte.ts`):
+- `triggerPostDownloadProcessing()` checks cache first — on hit, populates session state instantly and skips ffmpeg. On miss, extracts normally then saves to cache.
+- Thumbnails directed to cache dir via `getThumbnailCacheDir`
+- New `reprocessCurrentVideo()` export: clears cache entry and re-runs extraction
+
+**Preferences panel**: Cache management section showing total size and entry count with "Clear All Cache" button.
+
+**StatusBar**: Per-video "↻" reprocess button visible when processing is complete.
+
+**Dependency added**: `sha2 = "0.10"` for URL hashing.
+
+## Files Changed (15 files)
+
+### New Files (3)
+- `src-tauri/src/services/cache_manager.rs`
+- `src-tauri/src/commands/cache.rs`
+- `src/lib/bindings/cache.ts`
+
+### Modified Files (12)
+- `src/lib/timeline/renderer.ts`
+- `src/lib/components/Timeline.svelte`
+- `src/lib/stores/videoSession.svelte.ts`
+- `src-tauri/src/services/mod.rs`
+- `src-tauri/src/commands/mod.rs`
+- `src-tauri/src/lib.rs`
+- `src-tauri/Cargo.toml` + `Cargo.lock`
+- `src-tauri/src/commands/media_analysis.rs`
+- `src/lib/bindings/mediaAnalysis.ts`
+- `src/lib/components/PreferencesPanel.svelte`
+- `src/lib/components/StatusBar.svelte`
+- `VERSION`, `package.json`, `tauri.conf.json`
+
+## Test Results
+- **Rust**: 56 tests pass, 0 warnings
+- **Frontend**: svelte-check 0 errors/warnings, vitest 31/31 pass
+
+## Follow-Up Items
+- **HQ+toast edge case**: When video loaded with cached HQ file, `triggerPostDownloadProcessing` can still set `showUpgradeToast = true` even though playback is already HQ. Cosmetic — toast appears but does nothing harmful. Could add a guard `activeVideoPath !== exportFilePath` in a future pass.
+- **`now_iso8601` naming**: Function in `cache_manager.rs` returns Unix epoch seconds, not ISO 8601. Cosmetic naming issue.
+- **Caption cache dir**: `getCaptionCacheDir` is wired but not used yet — captions still go to temp dir. The manifest stores whatever path captions end up at. Could wire caption output to cache dir in a future pass for full persistence.
+- **Project files**: Cache manifest structure is designed as forward-looking scaffold for future project file save/load. No UI implemented yet.
+
+## Lessons Learned
+- Checking export cache before preview cache in `beginDownload()` was a clean refactor that simplified the flow — early return avoids duplicate logic.
+- Inlining waveform/keyframe data in JSON manifests works well for the data sizes involved (~2 MB worst case). No need for binary serialization.
+- The `#![allow(dead_code)]` at module scope in `cache_manager.rs` was pragmatic but broader than ideal — individual annotations would be more precise. Resolved naturally once Task 5 wired up the commands.