Sync chip: surface the strap backlog, with both counts inflected (#833)

Strand/BLE/BLEManager.swift

@@ -5927,6 +5927,9 @@ extension BLEManager: @preconcurrency CBCentralManagerDelegate {
         // re-derives it. (The honest flag is per-link, like the syncing pill / reject counters above.)
         whoop5EmptyOffload.reset()
         state.historySyncExperimental = false
+        // #689/#815: the backlog sample is "at connect" by definition, so it must not survive the link it
+        // was taken on — a stale figure under a fresh connection would be a plain lie.
+        state.pagesBehindAtConnect = nil
         lastBatteryReadAt = nil   // #battery: next connect's first enableLiveNotifications re-seeds the 5/MG battery reading
         // #612: the display flag only, not the underlying emptySyncTracker streak (that counter
         // deliberately survives a reconnect — unchanged, existing behaviour). A fresh link re-derives
@@ -6719,6 +6722,9 @@ extension BLEManager: @preconcurrency CBPeripheralDelegate {
         if !DataRange.isPendingResponse(frame, cmdOff: cmdOff) {
             if let pages = DataRange.pagesBehind(from: frame, cmdOff: cmdOff) {
                 log("Strap backlog pages behind: \(pages) (#689 — GET_DATA_RANGE ring backlog, diagnostic only)")
+                // #815: confirmed on both WHOOP 4.0 and 5.0/MG, so bank it unconditionally. The Today sync
+                // chip reads this while backfilling is true. Twin of the Android FrameRouter branch.
+                state.pagesBehindAtConnect = Int(pages)
             } else {
                 log("Strap backlog pages behind: not decodable from this frame (#689 — offsets may have moved; "
                     + "the raw frame above is the input). Diagnostic only, sync is unaffected.")

Strand/BLE/LiveState.swift

@@ -381,6 +381,16 @@ public final class LiveState: ObservableObject {
     /// experimental on 5.0" instead of a WHOOP-4-style "not recording"/sync-error. Reset on connect/disconnect.
     @Published public var historySyncExperimental: Bool = false
 
+    /// #689/#815 — the strap's ring-buffer page backlog, sampled ONCE from the connect-time
+    /// GET_DATA_RANGE reply and never re-polled mid-offload: the link is already firmware-paced, and #377
+    /// rules out re-polling just to feed a readout. So this is a figure AT CONNECT rather than a live one,
+    /// and the Today sync chip's copy says so — a static number under a "syncing" label otherwise reads as
+    /// a stalled live one. A bounded ring measure (write pointer − read pointer against the ring size),
+    /// never a percentage: the strap never reveals a total record count. Confirmed against real captures
+    /// on WHOOP 4.0 and 5.0/MG. nil before the first reply this session, or when the frame did not decode.
+    /// Twin of Android `LiveState.pagesBehindAtConnect`.
+    @Published public var pagesBehindAtConnect: Int? = nil
+
     /// #612 — true when the WHOOP-4/generic empty-offload streak (`EmptySyncTracker`, `BLEManager`) is
     /// currently SUSTAINED (3+ consecutive completed-but-empty offloads). Not 5/MG-specific and not
     /// coupled to HR: a connected strap that keeps handing over nothing has this true regardless of

Strand/Liquid/LiquidTodayView.swift

@@ -2735,9 +2735,19 @@ private struct LiquidBatteryButton: View {
             // VoiceOver announcing a real count while the ring showed the synthetic one — i.e. the
             // harness could not be used to check the read-out it exists to exercise.
             let n = syncChunks
-            return n > 0
-                ? String(localized: "Syncing strap history, \(n) chunks")
-                : String(localized: "Syncing strap history")
+            guard n > 0 else { return String(localized: "Syncing strap history") }
+            // #689/#815: the connect-time ring backlog, when the strap reported one. Zero is dropped by
+            // `SyncChipState.resolve`, and dropped here for the same reason: "0 pages behind" beside a
+            // running sync contradicts itself. Both counts inflect — the phrase is built from its own
+            // entry and joined through a template, so "1 chunk" and "1 page" read correctly and the
+            // joining punctuation stays inside the translated template rather than being concatenated.
+            let behind = live.pagesBehindAtConnect
+                .flatMap { $0 > 0 ? $0 : nil }
+                .map { String(localized: "\($0) pages behind at connect") }
+            if let behind {
+                return String(localized: "Syncing strap history, \(n) chunks, \(behind)")
+            }
+            return String(localized: "Syncing strap history, \(n) chunks")
         }
 
         switch batteryDisplay {