Persist private media delivery receipts

localPackages/BitFoundation/Sources/BitFoundation/PeerCapabilities.swift

@@ -28,6 +28,13 @@ public struct PeerCapabilities: OptionSet, Equatable, Hashable, Sendable {
     /// before outer BLE fragmentation. Peers that omit this bit require the
     /// signed directed raw-file migration fallback.
     public static let privateMedia = PeerCapabilities(rawValue: 1 << 8)
+    /// Stable private-media IDs are durably deduplicated by the receiver and
+    /// correlated delivery/read receipts permit bounded automatic resend.
+    ///
+    /// Bit 8 remains the encrypted-media compatibility contract. Bit 9 only
+    /// enables sender-side automatic retry after exact-session proof.
+    public static let privateMediaReceipts =
+        PeerCapabilities(rawValue: 1 << 9)
     /// Reserved for test builds that briefly advertised non-destructive Noise
     /// replacement. Current clients intentionally do not advertise or act on
     /// this bit; keep it decodable so the wire assignment is never reused.

localPackages/BitFoundation/Tests/BitFoundationTests/PeerCapabilitiesTests.swift

@@ -18,14 +18,30 @@ struct PeerCapabilitiesTests {
         #expect(PeerCapabilities.meshDiagnostics.encoded() == Data([0x40]))
         #expect(PeerCapabilities.privateMedia.encoded() == Data([0x00, 0x01]))
 
-        let high = PeerCapabilities(rawValue: 1 << 9)
-        #expect(high.encoded() == Data([0x00, 0x02]))
+        #expect(
+            PeerCapabilities.privateMediaReceipts.encoded()
+                == Data([0x00, 0x02])
+        )
         #expect(
             PeerCapabilities.nonDestructiveNoiseReplacement.encoded()
                 == Data([0x00, 0x04])
         )
 
-        let all: PeerCapabilities = [.prekeys, .wifiBulk, .gateway, .groups, .board, .vouch, .meshDiagnostics, .privateMedia]
+        let high = PeerCapabilities(rawValue: 1 << 11)
+        #expect(high.encoded() == Data([0x00, 0x08]))
+
+        let all: PeerCapabilities = [
+            .prekeys,
+            .wifiBulk,
+            .gateway,
+            .groups,
+            .board,
+            .vouch,
+            .meshDiagnostics,
+            .privateMedia,
+            .privateMediaReceipts,
+            .nonDestructiveNoiseReplacement
+        ]
         #expect(PeerCapabilities(encoded: all.encoded()) == all)
         #expect(PeerCapabilities(encoded: high.encoded()) == high)
         #expect(PeerCapabilities(encoded: PeerCapabilities([]).encoded()) == [])