filip d499fd8436 Client core hardening: X3DH session adoption, sync watermark, PoW, key rotation ...

- Adopt a new X3DH session (install into self.sessions + persist) only
  after the first message decrypts successfully. Previously
  _process_x3dh_header saved the candidate session immediately, so a
  replayed/forged X3DH header permanently overwrote a working ratchet.
- Advance the incremental-sync watermark (__last_server_ts) only across
  the prefix of messages settled in the cache. An undecryptable message
  (e.g. sender key not yet received) is re-fetched and retried up to
  _MAX_DECRYPT_RETRIES=3 times instead of being silently lost forever.
  Watermark is no longer touched on offset>0 pages and never regresses.
- Fix NameError in the proof-of-work registration path (logger ->
  self._logger) and run _solve_pow in an executor so it does not block
  the event loop.
- Persist the rotated RSA login key only after the server confirmed
  rotate_keys; writing private.pem first bricked the account when the
  request failed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

2026-06-12 16:08:31 +02:00

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