Root causes of the screenshot 404 incident:
1. RACE: client uploads image AND sends message concurrently; bot received
the message before the upload finished writing, so its GET hit a 404
error page (<100B treated as failure). FIX: _download_image now retries
3x with 2s backoff.
2. Zhiwei mentioned tesseract/小果 because the failure text never told her
the pipeline IS SenseNova. FIX: failure messages now name SenseNova
explicitly and ask for resend.
3. log_xmpp never worked for the bot: sys.path used relative '../..' from
a symlinked __file__ which resolved to '/' instead of MoFin root. This
is why the '最近对话' panel never had bot chat data (only cron script
entries). FIX: absolute path per red line #7. Verified: test message
now lands in xmpp_messages.jsonl.
4. My PowerShell -replace corrupted the file encoding (UnicodeDecodeError
crash loop on restart). Restored from git HEAD and re-applied edits with
the edit tool. Lesson: never use PowerShell string replace on UTF-8
source files with Chinese content.
5. functional_health: new sense_ocr module (OCR config presence +
SenseNova API TCP reachability), no token cost.
