diff --git a/apps/api/src/broker/outboxWorker.ts b/apps/api/src/broker/outboxWorker.ts
index 8c661c2..ab9af4f 100644
--- a/apps/api/src/broker/outboxWorker.ts
+++ b/apps/api/src/broker/outboxWorker.ts
@@ -333,7 +333,23 @@ async function dispatchRow(row: OutboxRow): Promise<DispatchResult> {
     return { success: true, conflict: false, hardFail: false, transient: false }
   }
 
-  // Unknown status — treat as transient to avoid silent data loss
+  // IN-02: an unmapped 4xx (e.g. 405, 409, 422) is a permanent client error — retrying it
+  // for the full backoff window just delays settling and burns the attempt budget before
+  // dead-lettering. The transient-eligible 4xx codes (408 request timeout, 429 too many
+  // requests) are already in TRANSIENT_STATUSES and handled above, so any remaining 4xx
+  // here is a hard fail. 5xx, network failures, and truly unknown statuses still fall
+  // through to transient so genuinely recoverable conditions keep their retries.
+  if (status >= 400 && status < 500) {
+    return {
+      success: false,
+      conflict: false,
+      hardFail: true,
+      transient: false,
+      error: `Hard fail: HTTP ${status} for uid=${row.uid}`,
+    }
+  }
+
+  // Unknown / 5xx status — treat as transient to avoid silent data loss
   return {
     success: false,
     conflict: false,