review: a session log that cannot be read now is waited out

The worker marked a turn failed on any error reading its log. A missing log,
a damaged line or a turn not found still fail it; any other I/O error is now
waited out with the outage's doubling wait, logged once when it starts and
once when the log reads again (pointer session-log-damaged, whose runbook
entry now covers it), shown by bxctl memory sync, and the turn stays waiting.

read_records tells an unreadable file from a damaged line (read_log is
unchanged). The message helpers move from worker.rs to honcho/messages.rs,
re-exported, to keep worker.rs under 500 lines.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/memoryd/src/honcho/mod.rs

@@ -6,6 +6,7 @@ pub mod config;
 pub mod decide;
 pub mod edits;
 pub mod ledger;
+pub mod messages;
 pub mod mirror;
 pub mod naming;
 pub mod report;