[dashboard DDX-22] S12: Dead-Letter Queues (queue + trigger)

[rickylabs]

DDX-22 / S12: Dead-Letter Queues (queue + trigger)

Summary

"Why did messages die across KV/Redis/Postgres, show depth, let me bulk-replay." Consolidated DLQ view for the queue and trigger dead-letter surfaces.

Scope

• DLQ depth stats-grid per backend; failed-message data-table with reason; bulk reprocess() action + CLI-equivalent + confirmationMessage.
• Data: DeadLetterRecord (reason/errorCode/payload), depth(), reprocess(); TriggerDlqPort (reason/attempts/replay).

Non-goals

• No log/trace ownership (out-link). No panel ships before its contract route exists.

Acceptance criteria

• Renders only once both co-req contract routes exist; bulk replay gated behind confirm.
• In ← S9 Triggers DLQ tab; in ← S7 for queue-backed workers.

Dependencies (BLOCKING — file co-req issues now)

(a) TriggerDlqPort contract route — #554; (b) packages/queue DeadLetterStore CLI/API — #555. Wave: later.