Log dedup: pending repeat summary is never flushed in non-TTY mode

[smolgroot]

Context

The log formatter (src/logger.rs) collapses consecutive identical log lines:

• TTY: the line is redrawn in place with an (xN) counter.

• Non-TTY (log files, journald, pipes): repeats are suppressed, and a summary line is emitted when the next different line arrives:

  22:41:12 INFO  blocked domain=collector.github.com. source_ip=127.0.0.1
  22:43:46 INFO  blocked domain=collector.github.com. source_ip=127.0.0.1 (repeated 411 more times)
  

Problem

In non-TTY mode, the summary is only written when a new, different event is logged. If the process exits while still receiving repeats — or if nothing different is ever logged — the final (repeated N more times) summary is lost. Those queries are still counted in server stats, but the log undercounts what happened.

Example: a client hammers a blocked domain, then the service is stopped. journald shows only the first blocked line; the N suppressed repeats are never accounted for.

Possible fix

The formatter only runs on new events, so it can't flush on its own. Options:

• A small background task (e.g. tokio interval) that flushes the pending dedup state if it's been idle for a few seconds.
• Additionally flush on graceful shutdown (the server already logs DNS server stopping..., which happens to trigger the summary — but only if shutdown is graceful).

The dedup state lives in CharmFormatter behind a Mutex<DedupState>; it would need to be shared with the flusher, and the flusher needs to write through the same stdout path to avoid interleaving.

Notes

• TTY mode is unaffected (the counter is redrawn live on every repeat).
• Low severity: only affects the trailing burst of repeats before exit/idle.