# Fresh Replay: Sync mod/master with upstream/master (continued)

## Task
Continue the "Fresh Replay" synchronization of mod/master with upstream/master (HEAD: 170cc25). This session picked up from Phase 2c (GfxRenderer/theme modifications) and completed through Phase 4 (verification).

## Changes Made

### Phase 2c-e: GfxRenderer, themes, SleepActivity, SettingsActivity, platformio
- Added `drawPixelGray` to GfxRenderer for letterbox fill rendering
- Added `PRERENDER_THUMB_HEIGHTS` to UITheme for placeholder cover generation
- Added `[env:mod]` build environment to platformio.ini
- Implemented sleep screen letterbox fill (solid/dithered) with edge caching in SleepActivity
- Added placeholder cover fallback (PlaceholderCoverGenerator) for XTC/TXT/EPUB sleep screens
- Added Clock settings category to SettingsActivity with timezone, NTP sync, set-time actions
- Replaced CalibreSettingsActivity with OpdsServerListActivity for OPDS server management
- Added DynamicEnum rendering support for settings
- Added long-press book management to RecentBooksActivity

### Phase 3: Re-port unmerged upstream PRs
- **#1055** (byte-level framebuffer writes): fillPhysicalHSpan*, optimized fillRect/drawLine/fillRectDither/fillPolygon
- **#1027** (word-width cache): 128-entry FNV-1a cache, hyphenation early exit (7-9% layout speedup)
- **#1068** (URL hyphenation): Already present in upstream
- **#1019** (file extensions in browser): Already present in upstream
- **#1090/#1185/#1217** (KOReader sync): Binary credential store, document hash caching, ChapterXPathIndexer
- **#1209** (OPDS multi-server): OpdsBookBrowserActivity accepts OpdsServer, directory picker, download-complete prompt
- **#857** (Dictionary): Activities already ported in Phase 1/2
- **#1003** (Placeholder covers): Already integrated in Phase 2

### Fixes
- Added `STR_OFF` i18n string for clock format setting
- Fixed include paths (ActivityResult.h from subdirectories)
- Replaced `Epub::isValidThumbnailBmp` with `Storage.exists()` (method doesn't exist in upstream)
- Replaced `StringUtils::checkFileExtension` with `FsHelpers` equivalents

### Image pipeline decision
- Kept upstream's JPEGDEC implementation — mod's picojpeg was a workaround for the older codebase
- No mod-specific image pipeline changes needed

## Branch Status
- **mod/master-resync**: 6 commits ahead of upstream/master (170cc25)
- **mod/backup-pre-sync-2026-03-07**: Safety snapshot of original mod/master
- 189 files changed, ~114,566 insertions, ~379 deletions vs upstream

## Follow-up Items
- Run full PlatformIO build on hardware to verify compilation
- Run clang-format on all modified files
- Test on device: clock display, sleep screen letterbox fill, dictionary, OPDS browsing
- KOReaderSyncActivity PUSH_ONLY mode (from PR #1090) not yet re-added to activity
- Consider adding `StringUtils.h` if other mod code needs `checkFileExtension`
- Update mod version string