Add geohash bulletin board: persistent signed notices over mesh sync

New MessageType 0x23 carries TLV-encoded board posts and tombstones,
self-signed with the author's Ed25519 key ("bitchat-board-v1" /
"bitchat-board-del-v1" domains) so notices verify without the author
present. BoardStore persists raw signed packets under Application
Support/board/ (200 posts, 5 per author, oldest evicted; expiry sweep;
tombstones retained until the deleted post's original expiry) and is
wiped on panic.

Board packets join gossip sync as bit 8 of the existing variable-length
types bitfield (a second byte old decoders already accept and ignore),
with a 60s round and its own capacity, served straight from the board
store so retention has one owner. Posts relay like broadcasts; urgent
posts get the announce-class TTL cap.

UI: a pin button in the header opens the board for the current channel
(geohash board, or mesh-local board), with urgent-pinned newest-first
listing, compose with urgent toggle and 1/3/7-day expiry, and
swipe-delete on own posts. Geohash posts also publish one-way as
Nostr kind-1 location notes when relays are reachable.

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

bitchatTests/Sync/GossipSyncBoardTests.swift

@@ -0,0 +1,130 @@
+//
+// GossipSyncBoardTests.swift
+// bitchatTests
+//
+// This is free and unencumbered software released into the public domain.
+// For more information, see <https://unlicense.org>
+//
+
+import BitFoundation
+import Foundation
+import Testing
+@testable import bitchat
+
+/// Board posts ride gossip sync through a provider that queries the board
+/// store, so retention (expiry, tombstones, caps) has a single owner.
+struct GossipSyncBoardTests {
+
+    private let myPeerID = PeerID(str: "0102030405060708")
+
+    private func makeBoardPacket(timestamp: UInt64) throws -> BitchatPacket {
+        BitchatPacket(
+            type: MessageType.boardPost.rawValue,
+            senderID: try #require(Data(hexString: "aabbccddeeff0011")),
+            recipientID: nil,
+            timestamp: timestamp,
+            payload: Data([0x42]),
+            signature: nil,
+            ttl: 7
+        )
+    }
+
+    private func quietConfig() -> GossipSyncManager.Config {
+        var config = GossipSyncManager.Config()
+        config.messageSyncIntervalSeconds = 0
+        config.fragmentSyncIntervalSeconds = 0
+        config.fileTransferSyncIntervalSeconds = 0
+        return config
+    }
+
+    @Test func boardRequestIsServedFromProvider() async throws {
+        let manager = GossipSyncManager(myPeerID: myPeerID, config: quietConfig(), requestSyncManager: RequestSyncManager())
+        let delegate = RecordingBoardDelegate()
+        manager.delegate = delegate
+        let boardPacket = try makeBoardPacket(timestamp: UInt64(Date().timeIntervalSince1970 * 1000))
+        manager.boardPacketsProvider = { return [boardPacket] }
+
+        let request = RequestSyncPacket(p: 4, m: 1, data: Data(), types: .board)
+        manager.handleRequestSync(from: PeerID(str: "FFFFFFFFFFFFFFFF"), request: request)
+
+        try await TestHelpers.waitFor({ delegate.packets.count == 1 }, timeout: TestConstants.shortTimeout)
+        let sent = try #require(delegate.packets.first)
+        #expect(sent.type == MessageType.boardPost.rawValue)
+        #expect(sent.isRSR)
+    }
+
+    @Test func nonBoardRequestDoesNotServeBoardPackets() async throws {
+        let manager = GossipSyncManager(myPeerID: myPeerID, config: quietConfig(), requestSyncManager: RequestSyncManager())
+        let delegate = RecordingBoardDelegate()
+        manager.delegate = delegate
+        let boardPacket = try makeBoardPacket(timestamp: UInt64(Date().timeIntervalSince1970 * 1000))
+        manager.boardPacketsProvider = { return [boardPacket] }
+
+        let request = RequestSyncPacket(p: 4, m: 1, data: Data(), types: .publicMessages)
+        manager.handleRequestSync(from: PeerID(str: "FFFFFFFFFFFFFFFF"), request: request)
+
+        // Follow with a board request; only its response should arrive, which
+        // also proves the first request produced nothing.
+        let boardRequest = RequestSyncPacket(p: 4, m: 1, data: Data(), types: .board)
+        manager.handleRequestSync(from: PeerID(str: "FFFFFFFFFFFFFFFF"), request: boardRequest)
+
+        try await TestHelpers.waitFor({ delegate.packets.count == 1 }, timeout: TestConstants.shortTimeout)
+        #expect(delegate.packets.count == 1)
+        #expect(delegate.packets.first?.type == MessageType.boardPost.rawValue)
+    }
+
+    @Test func maintenanceEmitsBoardRoundOnlyWithProvider() throws {
+        var config = quietConfig()
+        config.boardSyncIntervalSeconds = 1
+
+        // Without a provider the board schedule stays silent.
+        let unwired = GossipSyncManager(myPeerID: myPeerID, config: config, requestSyncManager: RequestSyncManager())
+        let unwiredDelegate = RecordingBoardDelegate()
+        unwired.delegate = unwiredDelegate
+        unwired._performMaintenanceSynchronously(now: Date())
+        #expect(unwiredDelegate.packets.isEmpty)
+
+        // With a provider, maintenance sends a board-typed request.
+        let manager = GossipSyncManager(myPeerID: myPeerID, config: config, requestSyncManager: RequestSyncManager())
+        let delegate = RecordingBoardDelegate()
+        manager.delegate = delegate
+        manager.boardPacketsProvider = { return [] }
+        manager._performMaintenanceSynchronously(now: Date())
+
+        #expect(delegate.packets.count == 1)
+        let payload = try #require(delegate.packets.first?.payload)
+        let request = try #require(RequestSyncPacket.decode(from: payload))
+        #expect(request.types == .board)
+    }
+}
+
+private final class RecordingBoardDelegate: GossipSyncManager.Delegate {
+    private let lock = NSLock()
+    private var _packets: [BitchatPacket] = []
+
+    var packets: [BitchatPacket] {
+        lock.lock()
+        defer { lock.unlock() }
+        return _packets
+    }
+
+    func sendPacket(_ packet: BitchatPacket) {
+        lock.lock()
+        _packets.append(packet)
+        lock.unlock()
+    }
+
+    func sendPacket(to peerID: PeerID, packet: BitchatPacket) {
+        lock.lock()
+        _packets.append(packet)
+        lock.unlock()
+    }
+
+    func signPacketForBroadcast(_ packet: BitchatPacket) -> BitchatPacket {
+        packet
+    }
+
+    func getConnectedPeers() -> [PeerID] {
+        []
+    }
+}