The Olm account pickle key is derived from the account ID plus the
configured device ID (acct:device_id). If the crypto store's account was
created before MATRIX_DEVICE_ID was set — e.g. the very first password
login, where the device ID is only known after connecting — it gets
pickled under "<acct>:default". Setting MATRIX_DEVICE_ID afterwards (a
reasonable thing to do once you know the device ID you want to pin)
changes the derived pickle key, and every subsequent unpickle attempt
fails with BAD_ACCOUNT_KEY. In optional-E2EE mode that failure is
swallowed and encryption silently stays disabled instead of surfacing an
actionable error.
_migrate_legacy_crypto_pickle() detects the BAD_ACCOUNT_KEY failure,
tries the known legacy pickle keys, and re-pickles the account (plus
every stored olm/megolm session — sessions share the same pickle key, so
migrating only the account would leave them unreadable on the next
decrypt and silently break key sharing with peers) under the current
key. It only reports failure when no known key can unpickle the
account, with a log message pointing at what changed.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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