Gateway mode: opt-in mesh↔Nostr uplink for geohash channels (#1384)

* Add capability bits to announce TLV

Announces now carry an optional capabilities TLV (0x05): a little-endian
bitfield with named bits for upcoming features (prekeys, wifiBulk,
gateway, groups, board, vouch, meshDiagnostics). Old clients skip the
unknown TLV; peers without it decode as nil so features can distinguish
"legacy peer" from "advertises nothing".

PeerCapabilities lives in BitFoundation with a minimal-length encoding
that preserves unknown bits for forward compatibility. Peer capabilities
are stored in the BLE peer registry on verified announce and exposed via
BLEService.peerCapabilities(_:). The local advertisement set is empty
until each feature ships its bit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Gateway mode: opt-in mesh↔Nostr uplink for geohash channels

An opt-in "internet gateway" toggle lets one connected phone bridge the
local geohash channel for mesh-only peers: signed kind-20000 events ride
a new nostrCarrier (0x28) packet — directed to the gateway for uplink,
broadcast with TTL for downlink — with Schnorr verification at every
hop, CourierStore-style quotas, and explicit loop-prevention rules.

- BitFoundation: MessageType.nostrCarrier = 0x28
- NostrCarrierPacket: 2-byte-length TLV codec (direction, geohash,
  signed event JSON), 16 KiB cap, tolerant decoder
- GatewayService: closure-injected policy layer — verify gates (sig,
  kind, #g tag, age, size), uplink quotas (10/min/depositor rate limit,
  offline queue of 20 total / 5 per depositor, drop-oldest, flush on
  reconnect), downlink budget (30/min, bounded drop-oldest backlog),
  bounded loop-prevention ID sets
- BLEService: runtime capability bits (advertise .gateway only while
  the toggle is on, re-announce on change), signed directed uplink
  sends, carrier ingress with depositor signature verification
- Mesh-only senders uplink automatically from sendGeohash when no relay
  is connected and a reachable peer advertises .gateway; once-per-
  channel "sent via mesh gateway" notice
- UI: gateway toggle beside the Tor toggle, globe header indicator,
  VoiceOver labels, xcstrings entries

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Gateway: harden downlink freshness, uplink verify ordering, and drain

Fixes the confirmed downlink/uplink defects from the PR #1384 review +
Codex findings:

- Downlink age + #g gate (Codex P2 / review #1): rebroadcastRelayEvent
  now drops events outside the same freshness window receivers enforce
  and whose #g tag mismatches the carrier geohash, BEFORE spending any
  budget — so a 1h/200-event channel-resubscribe backfill no longer
  burns the 30/min BLE budget on events every receiver drops.
- Rate-limit + dedup before Schnorr (review #2): handleUplinkDeposit now
  runs cheap structural checks + carried-ID dedup + rate-token consume
  before isValidSignature(), so a replay flood is bounded by cheap work
  instead of unbounded main-actor verifies.
- Quota-dropped deposits not rendered (review #3): enqueueUplink reports
  acceptance and injectInbound only fires for events actually
  published/queued, ending the local-timeline divergence.
- Drain timer + mark-after-send (Codex P2 / review #4): a burst beyond
  budget now arms a timer to drain when the window frees; rebroadcast
  IDs are marked only after an event is actually sent, so overflow-
  dropped events stay retryable.
- Symmetric publish path (review #5): the gateway publish closure now
  refuses when no geo relay is known, matching the local send path
  instead of publishing dead traffic to default relays.
- Loop-rule doc (review #7): softened to reflect that rule 3 is a
  call-site convention with unit-tested backstops; added tests for the
  publishedEventIDs backstop, downlink freshness/mismatch, drain timer,
  and quota-drop non-injection.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Gateway: stop self-echo of uplinked events onto the mesh

Every event a gateway uplinks to the relays comes back through its own
geohash subscription. `rebroadcastRelayEvent` deduped against
`meshBroadcastEventIDs`, `rebroadcastEventIDs`, and `pendingDownlinks`,
but not `publishedEventIDs` — so an event this gateway just published
was downlink-rebroadcast onto the same mesh it originated from, doubling
BLE airtime per uplinked message and able to starve the 30/min downlink
budget on a busy channel (device-confirmed, filed on #1384).

Fix: also skip the downlink rebroadcast when the event id is in
`publishedEventIDs`. That set is already the bounded (drop-oldest,
capacity maxTrackedEventIDs) loop-rule-2 uplink cache, populated only by
`publish()`, so genuine inbound-from-internet events (never published
here) still rebroadcast normally. Reconciles cleanly with the existing
loop-prevention sets — no new state.

Adds a GatewayServiceTests case asserting an uplinked event that echoes
back via the subscription is not rebroadcast, while a genuine inbound
event still is.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

localPackages/BitFoundation/Sources/BitFoundation/MessageType.swift

@@ -26,6 +26,10 @@ public enum MessageType: UInt8 {
     case fileTransfer = 0x22    // Binary file/audio/image payloads
     case boardPost = 0x23       // Signed geohash bulletin-board post or tombstone
 
+    // Gateway mode: signed Nostr event ferried between a mesh-only peer and
+    // an internet gateway peer.
+    case nostrCarrier = 0x28
+
     public var description: String {
         switch self {
         case .announce: return "announce"
@@ -38,6 +42,7 @@ public enum MessageType: UInt8 {
         case .fragment: return "fragment"
         case .fileTransfer: return "fileTransfer"
         case .boardPost: return "boardPost"
+        case .nostrCarrier: return "nostrCarrier"
         }
     }
 }