## Summary
* **What is the goal of this PR?** KOReader sync on a German-language
book would fail with an out-of-memory error when trying to open the
destination chapter after applying remote progress. The root cause was a
chain of two independent bugs that combined to exhaust the contiguous
heap needed by the EPUB inflate pipeline.
* **What changes are included?**
## Fix 1 — Hyphenation heap defragmentation (LiangHyphenation.cpp)
### What was happening
AugmentedWord, the internal struct used during Liang pattern matching,
held three std::vector<> members (bytes, charByteOffsets,
byteToCharIndex) plus a separate scores vector — a total of 4 heap
allocations per word during page layout. For a German-language section
with hundreds of words, thousands of small malloc/free cycles fragmented
the heap. Total free memory was adequate (~108 KB) but the largest
contiguous block shrank well below the 32 KB needed for the INFLATE ring
buffer used during EPUB decompression. The failure was invisible with
hyphenation disabled, where MaxAlloc stayed at ~77 KB; enabling German
hyphenation silently destroyed the contiguity the allocator needed.
### What changed
The three std::vector<> members of AugmentedWord and the scores vector
are replaced with fixed-size C arrays on the render-task stack:
```
uint8_t bytes[160] // was std::vector<uint8_t>
size_t charByteOffsets[70] // was std::vector<size_t>
int32_t byteToCharIndex[160] // was std::vector<int32_t>
uint8_t scores[70] // was std::vector<uint8_t> (local in liangBreakIndexes)
```
Sizing is based on the longest known German word (~63 codepoints × 2
UTF-8 bytes + 2 sentinel dots = 128 bytes); MAX_WORD_BYTES=160 and
MAX_WORD_CHARS=70 give comfortable headroom. The same analysis holds for
all seven supported languages (en, fr, de, es, it, ru, uk) — every
accepted letter encodes to at most 2 UTF-8 bytes after case-folding.
Words exceeding the limits are silently skipped (no hyphenation
applied), which is correct behaviour. The struct lives on the 8 KB
render-task stack so no permanent DRAM is consumed.
Verification: after the fix, MaxAlloc reads 77,812 bytes with German
hyphenation enabled — identical to the figure previously achievable only
with hyphenation off.
## Fix 2 — WiFi lifecycle in KOReaderSyncActivity
(KOReaderSyncActivity.cpp)
### What was happening
onEnter() called WiFi.mode(WIFI_STA) unconditionally before delegating
to WifiSelectionActivity. WifiSelectionActivity manages WiFi mode
internally (it calls WiFi.mode(WIFI_STA) again at scan start and at
connection attempt). The pre-emptive call from KOReaderSyncActivity
interfered with the sub-activity's own state machine, causing
intermittent connection failures that were difficult to reproduce.
Additionally, WiFi was only shut down in onExit(). If the user chose
"Apply remote progress" the activity exited without turning WiFi off
first, leaving the radio on and its memory allocated while the EPUB was
being decompressed — unnecessarily consuming the contiguous heap
headroom that inflate needed.
### What changed
* WiFi.mode(WIFI_STA) removed from onEnter(). WifiSelectionActivity owns
WiFi mode; KOReaderSyncActivity should not touch it before the
sub-activity runs.
* A wifiOff() helper (SNTP stop + disconnect + WIFI_OFF with settling
delays) is extracted into the anonymous namespace and called at every
web-session exit point:
- "Apply remote" path in loop() — before onSyncComplete()
- performUpload() success path
- performUpload() failure path
- onExit() (safety net for all other exit paths)
## Additional Context
* Add any other information that might be helpful for the reviewer
(e.g., performance implications, potential risks,
specific areas to focus on).
---
### AI Usage
While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.
Did you use AI tools to help write this code? _**YES**_ and two days of
blood, sweat and heavy swearing...
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