Dead letters

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A message becomes a dead letter when it cannot be delivered: the recipient was stopped, never existed, or the path was wrong. Nothing throws and nothing logs by default — tell returns, the sender carries on, and the work simply never happens. That silence is what makes the failure so easy to miss, and this panel is where it becomes visible.

Column	Meaning
time	When the message was captured
message	Constructor name of the message, or its `typeof`
recipient	The actor it failed to reach
sender	Who sent it, when there was a sender
replays	How many times it has been replayed and come back

Click a row to see the payload. A non-zero replays count is worth noticing: it means you are looking at a poison message being retried, not a fresh failure.

Switching the queue on

The panel reads the system’s dead-letter queue, and that queue is off by default — capturing every undelivered message costs memory, and a system that never produces one should not pay for it:

const systemOptions = ActorSystemOptions.create()
  .withDeadLetters({ store: 'memory', maxEntries: 500 });

const system = ActorSystem.create('orders', systemOptions);

With store: 'off' the panel stays in the navigation but reports itself unavailable, naming the setting to change. That is deliberate: an empty table cannot tell you whether nothing is broken or nothing is being recorded, and those are opposite answers.

Use store: 'persistent' to keep the queue across a restart — the letters are journalled, so the ones that arrived just before a crash are still there afterwards, which is usually exactly when you want them.

Filtering

The filter box takes a recipient path and keeps that actor and everything beneath it, so /user/orders selects the whole subtree and a full path selects one actor. The filtering happens on the server, over the ring it already holds; the summary counts what the filter selected, not what the page shows.

Payloads

Payloads are sanitised before they reach the browser — depth, entry count and string length are all capped. A message cut to fit says truncated above it, and one the queue could not keep at all says why instead of showing a null that reads like an empty message.

Replaying

Redelivering a captured letter is a queue operation rather than a panel one, and it stays in code on purpose — a button that re-sends production messages is a different kind of decision from a table that shows them:

const [letter] = await system.deadLetterQueue.list({ recipient: '/user/orders' });
if (letter !== undefined) await system.deadLetterQueue.replay(letter.id);

replay removes the entry before redelivering and remembers the message, so a second failure comes back as the same entry with a higher replayCount rather than as a fresh one. Past maxReplays the letter is quarantined and replay refuses it.