# Port PR #838 and PR #907 into fork

## Task
Cherry-pick / manually port two upstream PRs into the fork:
- **PR #907**: Cover image outlines to improve legibility
- **PR #838**: Fallback logic for epub cover extraction

## Changes Made

### PR #907 (cover outlines) — `src/components/themes/lyra/LyraTheme.cpp`
- Always draw a rectangle outline around cover tiles before drawing the bitmap on top
- Removed `hasCover` flag — simplified logic so outline is always present, preventing low-contrast covers from blending into the background

### PR #838 (cover fallback logic) — 3 files

#### `lib/Epub/Epub.h`
- Added declarations for 4 new methods: `generateInvalidFormatCoverBmp`, `generateInvalidFormatThumbBmp`, `isValidThumbnailBmp` (static), `getCoverCandidates` (private)
- Added doc comments on existing `generateCoverBmp` and `generateThumbBmp`

#### `lib/Epub/Epub.cpp`
- Added `#include <HalDisplay.h>` and `#include <algorithm>`
- **`generateCoverBmp`**: Added invalid BMP detection/retry, cover fallback candidate probing (`getCoverCandidates`), case-insensitive extension checking. Returns `false` on failure (no internal X-pattern fallback) so callers control the fallback chain
- **`generateThumbBmp`**: Same changes as `generateCoverBmp` — invalid BMP detection, fallback probing, case-insensitive check. Returns `false` on failure (no internal X-pattern fallback) so callers control the fallback chain
- **`generateInvalidFormatThumbBmp`** (new): Creates 1-bit BMP with X pattern as thumbnail marker
- **`generateInvalidFormatCoverBmp`** (new): Creates 1-bit BMP with X pattern as cover marker, using display dimensions
- **`isValidThumbnailBmp`** (new, static): Validates BMP by checking file size > 0 and 'BM' header
- **`getCoverCandidates`** (new, private): Returns list of common cover filenames to probe

#### `src/activities/home/HomeActivity.cpp`
- Replaced `Storage.exists()` check with `Epub::isValidThumbnailBmp()` to catch corrupt/empty thumbnails
- Added epub.load retry logic (cache-only first, then full build)
- After successful thumbnail generation, update `RECENT_BOOKS` with the new thumb path
- Thumbnail fallback chain: Real Cover → PlaceholderCoverGenerator → X-Pattern marker (epub only; xtc/other formats fall back to placeholder only)

## Adaptations from upstream PR
- All `Serial.printf` calls converted to `LOG_DBG`/`LOG_ERR` macros (fork convention)
- No `#include <HardwareSerial.h>` (not needed with Logging.h)
- Retained fork's `bookMetadataCache` null-check guards
- HomeActivity changes manually adapted to fork's `loadRecentCovers()` structure (upstream has inline code in a different method)
- Fork's `PlaceholderCoverGenerator` is the preferred fallback; X-pattern marker is last resort only

#### `src/activities/boot_sleep/SleepActivity.cpp`
- EPUB sleep screen cover now follows Real Cover → Placeholder → X-Pattern fallback chain
- Upgraded `Storage.exists()` check to `Epub::isValidThumbnailBmp()` for the epub cover path

#### `src/activities/reader/EpubReaderActivity.cpp`
- Cover and thumbnail pre-rendering now follows Real Cover → Placeholder → X-Pattern fallback chain
- Upgraded all `Storage.exists()` checks to `Epub::isValidThumbnailBmp()` for cover/thumb paths

## Follow-up Items
- Build and test on device to verify cover generation pipeline works end-to-end