diff --git a/logos_delivery/channels/reliable_channel.nim b/logos_delivery/channels/reliable_channel.nim
index de4365a3d..5a7ab24d4 100644
--- a/logos_delivery/channels/reliable_channel.nim
+++ b/logos_delivery/channels/reliable_channel.nim
@@ -403,8 +403,18 @@ proc onMessageReceived(
 
   ## SDS returns every payload deliverable now, in causal order — the
   ## message itself plus any parked segments it released. Empty = consumed
-  ## by SDS; `err` = not a decodable SDS envelope. Both drop here.
+  ## by SDS (parked or duplicate). `err` is a real ingress failure here: the
+  ## marker/contentTopic filter already ran, so surface it as an error event
+  ## rather than dropping it silently.
   let deliverable = (await self.sdsHandler.handleIncoming(plaintextBytes)).valueOr:
+    MessageErrorEvent.emit(
+      self.brokerCtx,
+      MessageErrorEvent(
+        requestId: RequestId(""),
+        messageHash: messageHash,
+        error: "SDS handleIncoming failed: " & error,
+      ),
+    )
     return
   for content in deliverable:
     self.reportReceived(content)
diff --git a/logos_delivery/channels/scalable_data_sync/scalable_data_sync.nim b/logos_delivery/channels/scalable_data_sync/scalable_data_sync.nim
index 975e02461..8da0c8530 100644
--- a/logos_delivery/channels/scalable_data_sync/scalable_data_sync.nim
+++ b/logos_delivery/channels/scalable_data_sync/scalable_data_sync.nim
@@ -9,10 +9,10 @@
 {.push raises: [].}
 
 import std/[options, tables]
+from std/times import initDuration, getTime, toUnix, nanosecond
 import results, chronos, chronicles
 import nimcrypto/keccak
 import stew/byteutils
-from std/times import initDuration, getTime, toUnix, nanosecond
 
 import sds
 import message as sds_message
@@ -27,8 +27,10 @@ const
   DefaultAcknowledgementTimeoutMs* = 5_000
   DefaultMaxRetransmissions* = 5
   DefaultCausalHistorySize* = 2
-  MaxPendingContent = 1024
+  MaxPendingContent = 32
     ## Bound on segments parked while their causal dependencies are missing.
+    ## Kept small on purpose: at ~100KiB max per segment, 32 caps the stash
+    ## at ~3MiB per channel. Raise only if a real backlog need shows up.
 
 type
   SdsConfig* = object
@@ -43,7 +45,7 @@ type
     ## Invoked with a full SDS envelope to rebroadcast (SDS-R repair).
 
   SdsHandler* = ref object
-    rm: ReliabilityManager
+    reliabilityManager: ReliabilityManager
     channelId: SdsChannelID
     pendingContent: OrderedTable[SdsMessageID, seq[byte]]
       ## Segments parked until their causal dependencies arrive.
@@ -74,9 +76,11 @@ proc computeMessageId(self: SdsHandler, payload: seq[byte]): SdsMessageID =
 proc installCallbacks(self: SdsHandler) =
   ## Direct field assignment is race-free here: no periodic task or protocol
   ## op has started yet.
-  self.rm.onMessageReady = proc(
+  self.reliabilityManager.onMessageReady = proc(
       messageId: SdsMessageID, channelId: SdsChannelID
   ) {.gcsafe.} =
+    ## An SDS "message" is one channel segment here — each segment is wrapped
+    ## into its own SDS message — so this is effectively `onSegmentReady`.
     ## Fires during unwrap, under the manager lock — must stay synchronous.
     ## Collect only; `handleIncoming` delivers after the direct content.
     ## The manager owns a single channel, so `channelId` is always ours; the
@@ -86,12 +90,12 @@ proc installCallbacks(self: SdsHandler) =
       self.released.add(self.pendingContent.getOrDefault(messageId))
       self.pendingContent.del(messageId)
 
-  self.rm.onMessageSent = proc(
+  self.reliabilityManager.onMessageSent = proc(
       messageId: SdsMessageID, channelId: SdsChannelID
   ) {.gcsafe.} =
     debug "SDS message acknowledged", channelId, messageId
 
-  self.rm.onMissingDependencies = proc(
+  self.reliabilityManager.onMissingDependencies = proc(
       messageId: SdsMessageID, missingDeps: seq[HistoryEntry], channelId: SdsChannelID
   ) {.gcsafe.} =
     ## Recovery via SDS sync / SDS-R for now; targeted store fetch by
@@ -99,7 +103,9 @@ proc installCallbacks(self: SdsHandler) =
     debug "SDS message has missing dependencies",
       channelId, messageId, missing = missingDeps.len
 
-  self.rm.onRepairReady = proc(message: seq[byte], channelId: SdsChannelID) {.gcsafe.} =
+  self.reliabilityManager.onRepairReady = proc(
+      message: seq[byte], channelId: SdsChannelID
+  ) {.gcsafe.} =
     if not self.onRebroadcast.isNil():
       self.onRebroadcast(message)
 
@@ -120,7 +126,7 @@ proc new*(
     participantId, reliabilityConfig, config.persistence.get(noOpPersistence())
   )
   let handler = T(
-    rm: rm,
+    reliabilityManager: rm,
     channelId: channelId,
     pendingContent: initOrderedTable[SdsMessageID, seq[byte]](),
     released: @[],
@@ -135,11 +141,11 @@ proc start*(self: SdsHandler) =
   ## lazily on first use: `wrapOutgoing` and `handleIncoming` both ensure
   ## the channel, and `handleIncoming` loads before its duplicate check so a
   ## replay right after a restart is still caught.
-  self.rm.startPeriodicTasks()
+  self.reliabilityManager.startPeriodicTasks()
 
 proc stop*(self: SdsHandler) {.async: (raises: []).} =
   ## Cancels the background loops. Persisted state is left intact.
-  await self.rm.cleanup()
+  await self.reliabilityManager.cleanup()
 
 proc wrapOutgoing*(
     self: SdsHandler, payload: seq[byte]
@@ -147,7 +153,7 @@ proc wrapOutgoing*(
   ## Wraps a segment with reliability metadata and registers it in the SDS
   ## outgoing buffer awaiting end-to-end acknowledgement.
   let wrapped = (
-    await self.rm.wrapOutgoingMessage(
+    await self.reliabilityManager.wrapOutgoingMessage(
       payload, self.computeMessageId(payload), self.channelId
     )
   ).valueOr:
@@ -160,7 +166,7 @@ proc handleIncoming*(
   ## Returns the payloads deliverable now, in causal order. Empty when SDS
   ## consumed the message; `err` when the bytes are not an SDS envelope.
   let msg = deserializeMessage(wire).valueOr:
-    return err("SDS deserialization failed")
+    return err("SDS deserialization failed: " & $error)
 
   ## Pre-filter: `unwrapReceivedMessage` auto-creates the channel it sees on
   ## the wire, so foreign traffic must not reach it.
@@ -169,48 +175,63 @@ proc handleIncoming*(
       channelId = self.channelId, wireChannelId = msg.channelId
     return ok(newSeq[seq[byte]]())
 
+  ## Only the lock acquisition can raise (CancelledError); the unwrap work
+  ## below is `raises: []`, so the try stays scoped to exactly the acquire.
   try:
     await self.ingressLock.acquire()
-    try:
-      ## Load persisted state before the duplicate check, so a replay right
-      ## after a restart is not re-delivered. Idempotent, cheap once loaded.
-      (await self.rm.ensureChannel(self.channelId)).isOkOr:
-        return err("SDS ensureChannel failed: " & $error)
+  except CancelledError:
+    return err("SDS handleIncoming cancelled before acquiring ingress lock")
 
-      ## The unwrap result does not distinguish first delivery from
-      ## duplicate, so capture delivered-before up front.
-      let ctx = self.rm.channels.getOrDefault(self.channelId)
-      let isDuplicate = not ctx.isNil() and msg.messageId in ctx.messageHistory
+  ## Funnel every unwrap outcome into `res` so the lock is released once on
+  ## the tail path, where `releaseIngressLock` can surface its own error.
+  var res: Result[seq[seq[byte]], string]
+  block ingress:
+    ## Load persisted state before the duplicate check, so a replay right
+    ## after a restart is not re-delivered. Idempotent, cheap once loaded.
+    (await self.reliabilityManager.ensureChannel(self.channelId)).isOkOr:
+      res = err("SDS ensureChannel failed: " & $error)
+      break ingress
 
-      self.released.setLen(0)
-      let unwrapped = (await self.rm.unwrapReceivedMessage(wire)).valueOr:
-        return err("SDS unwrap failed: " & $error)
+    ## The unwrap result does not distinguish first delivery from
+    ## duplicate, so capture delivered-before up front.
+    let ctx = self.reliabilityManager.channels.getOrDefault(self.channelId)
+    let isDuplicate = not ctx.isNil() and msg.messageId in ctx.messageHistory
 
-      if isDuplicate:
-        return ok(newSeq[seq[byte]]())
+    self.released.setLen(0)
+    let unwrapped = (await self.reliabilityManager.unwrapReceivedMessage(wire)).valueOr:
+      res = err("SDS unwrap failed: " & $error)
+      break ingress
 
-      if unwrapped.missingDeps.len > 0:
-        if self.pendingContent.len >= MaxPendingContent:
-          var oldest: SdsMessageID
-          for k in self.pendingContent.keys:
-            oldest = k
-            break
-          self.pendingContent.del(oldest)
-          warn "SDS pending-content stash full, dropping oldest entry",
-            channelId = self.channelId, dropped = oldest
-        self.pendingContent[msg.messageId] = unwrapped.message
-        return ok(newSeq[seq[byte]]())
+    if isDuplicate:
+      res = ok(newSeq[seq[byte]]())
+      break ingress
 
-      var deliverable = newSeq[seq[byte]]()
-      if unwrapped.message.len > 0:
-        ## Empty content is sync traffic: causal metadata only.
-        deliverable.add(unwrapped.message)
-      deliverable.add(self.released)
-      self.released.setLen(0)
-      return ok(deliverable)
-    finally:
-      self.ingressLock.release()
-  except CatchableError:
-    return err("SDS handleIncoming failed: " & getCurrentExceptionMsg())
+    if unwrapped.missingDeps.len > 0:
+      if self.pendingContent.len >= MaxPendingContent:
+        var oldest: SdsMessageID
+        for k in self.pendingContent.keys:
+          oldest = k
+          break
+        self.pendingContent.del(oldest)
+        warn "SDS pending-content stash full, dropping oldest entry",
+          channelId = self.channelId, dropped = oldest
+      self.pendingContent[msg.messageId] = unwrapped.message
+      res = ok(newSeq[seq[byte]]())
+      break ingress
+
+    var deliverable = newSeq[seq[byte]]()
+    if unwrapped.message.len > 0:
+      ## Empty content is sync traffic: causal metadata only.
+      deliverable.add(unwrapped.message)
+    deliverable.add(self.released)
+    self.released.setLen(0)
+    res = ok(deliverable)
+
+  try:
+    self.ingressLock.release()
+  except AsyncLockError as e:
+    return err("SDS ingress lock release failed: " & e.msg)
+
+  return res
 
 {.pop.}