Transcript Incremental Projection

Nucleic-Session: 0FFD007B-0696-4517-9429-129C7B0FD5AC
Co-authored-by: Nucleic <[email protected]>

NucleicRemote/NucleicRemote/Models/HostConnection.swift

@@ -584,6 +584,12 @@ final class HostConnection {
             // Session-transfer replies (mesh P5) only reach a *source* Mac; a phone is never one.
             break
         case .transcriptChunk(let chunk):
+            // A slice of a *background prefetch*: accumulate it whole — it never touches the
+            // open transcript's cursor/dedup state, which belongs to the on-screen session.
+            if chunk.requestID == prefetchRequestID {
+                if chunk.sessionID == prefetchSessionID { prefetchEvents.append(contentsOf: chunk.events) }
+                break
+            }
             // One ordered slice of the full-history fetch we started on open. Match on request id so
             // a stale batch from a previous open (session switched underneath us) is ignored.
             guard chunk.requestID == transcriptFetchRequestID, chunk.sessionID == openSessionID else { break }
@@ -595,10 +601,12 @@ final class HostConnection {
             if let maxSeq = chunk.events.map(\.seq).max() { openMaxSeq = max(openMaxSeq ?? 0, maxSeq) }
             if !fresh.isEmpty { callbacks.openBackfill(EventBatch(sessionID: chunk.sessionID, events: fresh)) }
         case .transcriptFetchComplete(let done):
+            if done.requestID == prefetchRequestID { finishPrefetch(delivering: true); break }
             // Terminal success — every batch shipped. Clear the in-flight id; the cursor/dedup state
             // is already advanced by the chunks above.
             if done.requestID == transcriptFetchRequestID { transcriptFetchRequestID = nil }
         case .transcriptUnavailable(let un):
+            if un.requestID == prefetchRequestID { finishPrefetch(delivering: false); break }
             // The host holds no transcript for this session (or can't serve the format). The cold tail
             // still shows; there's just no deeper history to add. Clear the in-flight id.
             if un.requestID == transcriptFetchRequestID { transcriptFetchRequestID = nil }