## Summary
* **What is the goal of this PR?**
Fixes#2275. A book could get stuck reopening on an old page, with
progress no
longer saving and neither "Delete Book Cache" nor "Clear Reading Cache"
able to
fix it. Root cause: `progress.bin` was written truncate-in-place, so an
interrupted write (power loss, or a crash mid-SPI during sleep) left it
with a
broken FAT cluster chain that the firmware could neither rewrite nor
delete —
recovery required `fsck`/manual deletion on a host PC.
Confirmed in the SDK: `SDCardManager::openFileForWrite` opens with
`O_RDWR | O_CREAT | O_TRUNC`, so the canonical file is zeroed before the
few
progress bytes are rewritten — exactly the window that corrupts the FAT
chain.
* **What changes are included?**
* New shared helper `ProgressFile::writeAtomic()`
(`src/activities/reader/ProgressFile.h`): writes progress to
`progress.bin.tmp`, flushes and closes it, then `remove`s the old
`progress.bin` and `rename`s the temp into place. An interrupted write
now
only ever damages the throwaway temp; the canonical file is never torn.
* All three readers route their progress saves through the helper:
EPUB (`EpubReaderUtils.h`), `TxtReaderActivity`, `XtcReaderActivity` —
they
all shared the identical vulnerable pattern.
* Minor: `EpubReaderUtils::saveProgress` now takes `const Epub&` (clears
a
cppcheck `constParameterReference` finding).
## Additional Context
* **Crash-safe, not metadata-atomic.** On FAT the replace is `remove` +
`rename`
(two directory ops; SdFat's `rename` won't overwrite, hence
remove-first). A
crash between them leaves *neither* file, which reads as "no saved
progress" on
next launch — a harmless reset to an old page, never a
corrupt/unclearable file.
The guarantee is that `progress.bin` is never half-written.
* **Prevents, does not repair.** This stops new corruption on healthy
cards. It
cannot fix an already-corrupted `progress.bin` (removing it may itself
fail at
the FAT level) — those still need `fsck`/manual deletion, as in the
issue's
workaround.
* **Known follow-up (out of scope here):** a crash *while writing the
temp* can
leave an orphan `progress.bin.tmp`. It's harmless and self-healing (the
next
save overwrites it, and it never blocks reading progress), but a
boot-time
orphan-`.tmp` cleanup would be a tidy follow-up.
* **Focus areas for review:** the close-before-rename ordering in
`ProgressFile.h` and the remove-before-rename rationale.
## Verification
* `./bin/clang-format-fix` — clean
* `pio check --fail-on-defect low --fail-on-defect medium
--fail-on-defect high` — no defects
* `pio run` — SUCCESS (RAM 30.9%, Flash 78.8%; footprint essentially
unchanged)
* Tested on a **Xteink X4** device: open book, turn pages, sleep/exit,
reopen —
progress now restores to the navigated page across all three readers
(EPUB / TXT / XTC).
---
### AI Usage
Did you use AI tools to help write this code? _**YES**_
---------
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
