Two good questions.

Concurrent sessions: it's a real edge case but the blast radius is small. Daily logs are append-only by convention, so two sessions writing at the same time would mean interleaved or lost entries at worst. Registers and CLAUDE.local.md are theoretically higher risk since they get modified rather than appended to, but promotion is user-initiated via /recall-promote, so you'd have to be promoting in both sessions at the same time to hit it. The race window exists (edit tool does read-then-write, not atomic append) but I haven't hit it in practice.

Cleanest fix if it ever matters: per-session log files (YYYY-MM-DD-session-abc.md) so there's no conflict on capture, and recall-promote just reads all of them. Not worth adding file locking or restructuring for a problem that hasn't bitten anyone yet.

Write gate consistency: in my experience the model errs conservative (misses things) rather than permissive (saves junk). For me I actually prefer that direction since saving too much degrades the whole system over time, while missing something important is easy to fix. You just say "remember this" and it bypasses the gate. That explicit override (item 5 on the gate) has been more reliable than trying to tune the automatic criteria to be more permissive.