Expand preview handling and search coverage

TODO.md

@@ -32,6 +32,7 @@
 - A fresh-machine bootstrap was revalidated in a user-local toolchain setup on `2026-03-17`; `go test ./...` and `bash scripts/selftest.sh` now pass in that setup.
 - Result modal sizing is now being constrained to the viewport, and modal-only source-summary translation is now part of the active implementation path.
 - Card summaries now also translate lazily to Korean, and Gemini negative-assessment handling now drives stronger follow-up search behavior than before.
+- Search preview delivery is now moving away from persistent on-disk preview caching toward live proxy / live transcode behavior, with Google Video preview reuse added to result cards and modal playback.
 
 ## Current Architecture
 - `backend/main.go`
@@ -229,6 +230,7 @@
 - Gemini notes are now intended to be Korean, but final output quality still depends on Gemini response consistency.
 - Source Summary translation now depends on Google Translate HTTP availability; frontend silently falls back to original summary text if translation fails.
 - The result modal should now stay within viewport height, but this still needs real browser confirmation on multiple short-height displays because CSS-only constraints were the source of the latest user-visible regression.
+- Artgrid preview playback now has a server-side ffmpeg transcode path for `.m3u8` style preview URLs, but this trades storage savings for runtime CPU cost.
 - The local self-test script is better than before, but it is still a smoke test, not full integration coverage.
 
 ## Current Risks Around Search Quality
@@ -553,6 +555,7 @@
 - [ ] Improve Envato / Artgrid preview acquisition reliability so Gemini Vision sees real frames more often
 - [ ] Browser-verify the new result modal at multiple viewport heights and confirm translated Source Summary readability on real long descriptions
 - [ ] Evaluate whether the new Gemini supplemental-query generation is reducing irrelevant results on a small fixed benchmark query set
+- [ ] Measure runtime cost of live Artgrid preview transcoding and decide whether bounded in-memory throttling or concurrency caps are needed
 - [ ] Revisit Google Video UX:
   - current YouTube embed was abandoned due error `153`
   - current in-app panel is more reliable but less rich than a true embedded watch page
@@ -618,6 +621,24 @@
 - If behavior in the browser does not match the latest backend/frontend code, the first assumption should be stale frontend assets until proven otherwise
 
 ## Recent Change Log
+- Date: `2026-03-17`
+- What changed:
+  - If the first search pass plus Gemini filtering still leaves too few visible results, the backend now performs an additional coverage-expansion search/evaluation pass before final fallback filling.
+  - Search result cards and the result modal now reuse the existing direct-download preview probe path for Google Video, so YouTube-backed results can surface actual playable preview streams instead of staying thumbnail-only.
+  - Artgrid-style `.m3u8` previews now have a server-side ffmpeg transcode route so the frontend can request a directly playable MP4 stream when plain HLS playback is unreliable.
+  - Persistent preview-file caching to disk was removed from the preview proxy path so one-off preview traffic does not keep accumulating files under the downloads cache area.
+  - Modal spacing, media height, and text sizing were tightened again so the popup is more likely to fit without scrolling on shorter displays.
+- Why it changed:
+  - The latest user feedback said the search result count had become too low after stricter Gemini filtering, the popup still felt too large, Google Video already had a better preview path in direct-download mode, Artgrid previews still were not reliably playable, and the server should prefer not retaining disposable preview artifacts on disk.
+- How it was verified:
+  - `go test ./...`
+  - `bash scripts/selftest.sh`
+  - `python3 -m py_compile worker/downloader.py scripts/mock_searxng.py`
+- What is still risky or incomplete:
+  - The extra coverage-expansion pass can improve visible count but may increase latency when upstream SearXNG quality is poor.
+  - Live ffmpeg transcoding avoids preview-file accumulation but may become CPU-heavy under concurrent preview playback.
+  - Real browser validation is still needed for the exact viewport in the latest screenshot and for actual Artgrid preview playback behavior.
+
 - Date: `2026-03-17`
 - What changed:
   - Removed the visible `AI Recommended` badge from search cards.